Letters Influenza vaccine effectiveness, 2010/11 23

This report describes 326 cases of nosocomial transmission of measles with 286 cases among non-healthcare workers who acquired the disease in a hospital setting. Between October 2009 and April 2010, 40 healthcare workers from seven different regions in Bulgaria have contracted the disease.


Outbreak overview
The current outbreak in Bulgaria started in March 2009 following an imported case of measles from Germany [2].It has been the largest outbreak ever reported in Bulgaria since the large outbreak which occurred in 1976, only a few years after the immunisation schedule with one dose of monovalent measles-containing vaccine starting with the age of 10 months had been implemented in the country.The second dose was introduced at four years of age in 1982.In 1993 the first dose of monovalent measles-containing vaccine was replaced by the MMR vaccine.Since 2001 the twodose measles immunisation with MMR vaccine has been introduced with the first dose at 13 months and the second at 12 years of age [3].
In this outbreak, the total number of cases reached 24,253 during the two-year period, reached its peak in March 2010 and started gradually to subside in late summer [unpublished data].Only a few cases were reported every week in September and October 2010 [3].However, according to preliminary results, about 130 cases were notified in the first three months of 2011, some of them diagnosed in late December 2010 but notified in January 2011.This calls into question whether it is at all possible to control such a contagious disease in a short time and in the presence of many pockets of susceptible individuals.
Of the 24,137 cases with full epidemiological and clinical data available, 3,917 (16.2%) were laboratoryconfirmed (measles IgM), 7,944 (32.9%) were epidemiologically linked and the remaining 12,276 (50.9%) were probable cases.The highest incidence rate was observed in children under one year of age (n=4,717; 6/100,000 population) who were not eligible for MMR vaccination.Despite the ongoing outbreak, the Bulgarian health authority did not change the recommendation regarding MMR vaccination, i.e. did not recommend the first dose to be given earlier, at the age of nine months.Of the 24,047 cases investigated, 89.3% belonged to the Roma ethnic community.The majority (86.8%) were hospitalised, mainly due to epidemiological considerations -patients from overcrowded households with poor living conditions and inadequate access to medical care.Twenty-four deaths were reported but no information on complications is available at the moment [4].

Transmission in medical settings
Transmission in medical settings was reported for 326 cases and the hospital was the most frequently reported setting.Of these 326 cases, 286 were not healthcare workers and acquired measles in hospital or primary care.
By April 2010, 40 healthcare workers (HCWs) (0.16% of all measles cases) in seven different regions in Bulgaria have contracted the disease.Most of them occurred during the peak of the outbreak, in March 2010.The measles case definition in Bulgaria is based on the EU case definition [5].Twenty-three cases were classified as confirmed (presence of measles-specific IgM antibodies) and 17 as probable (not tested).Laboratory tests of all but two were performed at the National Reference laboratory of measles, mumps and rubella in Sofia.Thirty-four cases occurred in hospitals and six in primary care.
The mean age of the cases among HCWs was 38 years (range 24-48 years) and 28 of them were women.The largest group of measles cases among HCWs were physicians (n=19), followed by laboratory technicians (n=8), nurses (n=7), cleaning staff (n=4) and pharmacists (n=2).All but one are likely to have acquired the infection from patients and one physician from a colleague.Ten HCWs developed radiologically proven pneumonia and all recovered.Fifteen HCWs were hospitalised due to dehydration or pneumonia.
According to their age, the majority of cases should have been vaccinated with at least one dose of measles-containing vaccine, as one dose measles immunisation was introduced in Bulgaria in 1969 and in 1972 it became part of the immunisation schedule in the whole country.Nevertheless, only one case had a vaccination record of two doses of measles-containing vaccine; the rest did not know their vaccination status.
No secondary cases among other contact patients and family members were reported.Information about susceptibility status or post-exposure prophylaxis of the HCWs' contacts was not available.

Control measures
Two supplementary MMR vaccination campaigns were implemented.The first one started on 27 April 2009 and targeted all individuals aged between 13 months and 30 years in the affected regions (Razgrad, Shumen, Silistra and Dobrich), who had not undergone the full vaccination with two doses.Later, in order to increase the vaccine coverage, a second campaign was directed towards those older than 30 years without documented measles vaccination [4].These measures were not very effective maybe because they were not implemented simultaneously for all 28 regions in Bulgaria.On the other hand, a large number of cases might have received a supplementary vaccine dose when already infected with measles virus.Post-exposure immunoglobulin for people at risk for a severe form of the disease was not routinely given.The full analysis of the outbreak is still in progress.

Discussion
Measles among HCWs accounts for a relatively small proportion of the reported cases but is important because of the potential for transmission of the disease to susceptible colleagues (thereby disrupting healthcare service), high-risk patients such as pregnant women, immunocompromised individuals, and family members.They have a nearly 19-fold higher risk of acquiring measles than the general population [6].Transmission among HCWs was also reported in France in 2010 [7,8].The Advisory Committee on Immunization Practice in the United States of America recommends all healthcare personnel to have presumptive evidence of immunity (positive serological test results or written evidence of appropriate (two doses) immunisation to mumps, measles and rubella or being born before 1957).For unvaccinated persons born after 1957 who lack evidence of mumps, measles and/or rubella immunity or laboratory confirmation of the disease, healthcare facilities should recommend two doses of MMR vaccine during an outbreak of mumps or measles and one dose during an outbreak of rubella [9].European countries in general should recommend measles vaccine for HCWs who do not have documented vaccination record or history of the disease.This outbreak highlights the need for further activities with respect to vaccinating non-immune HCWs.Moreover, it illustrates that a high rate of hospitalisation for measles poses a risk for nosocomial infections that may have a detrimental effect on certain immunocompromised or non-immune patients and HCWs.Therefore, strict hygiene measures are important to prevent the spread in hospital settings.
The 40 cases of measles identified in HCWs in the course of this outbreak further highlights the need for such recommendations.Increased vaccine uptake among HCWs of other contagious diseases like varicella and influenza also needs to be considered in medical settings.Maintaining a high immunisation coverage and strengthening surveillance are essential if Europe is to meet the new elimination target of 2015.

Introduction
Infection with Salmonella enterica subsp.enterica serotype Enteritidis (S.Enteritidis) remains an important public health problem in Europe and other parts of the world [1][2][3][4].Outbreaks caused by Salmonella infection have been associated with a variety of foods; however, outbreaks caused by Salmonella Enteritidis infection are closely associated with eggs and egg products [2,5,6].In September 2009, the Department of Gastrointestinal, Emerging and Zoonotic Infections at the Health Protection Agency (HPA) reported a marked upsurge in the number of non-travel-related human cases of infection with S. Enteritidis phage type (PT) 14b with resistance to nalidixic acid and partial resistance to ciprofloxacin (S.Enteritidis PT 14b NxCp L ).Infectious diseases resulting from food poisoning are statutorily notifiable in England and Wales: cases are notified by registered medical practitioners and diagnostic laboratories to the HPA.In total, 572 cases of S. Enteritidis PT 14b NxCp L infection were reported between January and December 2009, compared with 141 in 2008.Between 1 September and 31 December 2009, there were 489 cases.There were 14 recognised, discrete local outbreaks of S. Enteritidis PT 14b NxCp L infection in England and two in Wales between August and December 2009 (HPA unpublished data).All but one of these outbreaks were linked to food-service premises; the remaining outbreak was linked to a residential care home for the elderly.The total number of reported cases associated with these outbreaks was 152: six were hospitalised and two deaths were reported.
Preliminary investigations of these 16 outbreaks suggested putative links to infected eggs, with evidence of cross-contamination of S. Enteritidis PT 14b NxCp L to other foods, particularly ready-to-eat vegetarian foods.The outbreak strain was isolated from samples of eggs, egg mayonnaise, egg-fried rice, pooled liquid egg mix and work surfaces in the food-service premises investigated as part of the outbreak investigations.Eggs collected from these premises (five restaurants serving Chinese or Thai cuisine and two cafes) in seven of the outbreaks were from the same production establishment in Spain, as indicated by the stamp on the egg shells.We therefore conducted a case-control analysis to determine whether the likely source of infection in the apparently sporadic cases was the same as that for cases in the outbreaks.
Before the upsurge in S. Enteritidis PT 14b NxCp L infections in September 2009, there had been other sustained increases in the incidence of S. Enteritidis non-PT4 infections in England and Wales between 2000 and 2004 [7,8].Epidemiological and microbiological investigations and a case-control study of primary sporadic indigenous cases found that consumption of eggs from food prepared outside the home was associated with being a case.The investigations identified eggs sourced from Spain used in the food-service sector as the main cause of the increase [1,2,7,8].In the United Kingdom (UK), the predominant PT responsible for egg-borne S. Enteritidis infection had been PT 4 between 1992 and 2002 [5].Following large epidemics of S. Enteritidis infection in the UK in the late 1980s, mainly due to PT 4, a decline in human S .Enteritidis PT 4 infection in England and Wales occurred from 1997, largely because of industry control programmes in the poultry sector, including vaccination of layer flocks [9].Since 2000, egg-associated S. Enteritidis PTs other than PT 4 causing human infection have emerged, with the greatest increases occurring in S. Enteritidis PT 1and PT 14b-related infections [7].
Surveillance of salmonellosis from 1998 to 2003 also showed upsurges in S. Enteritidis non-PT4 infections in other European countries [1].Between 1998 and 2003, the proportion of PT4 infections fell from 61.8% in 1998 to 32.1% in 2003, with a concomitant increase in S. Enteritidis non-PT4 infections (including PT1, 8, 14b and 21) in Austria, Germany, Spain, Denmark, Finland, England, Wales and Northern Ireland, Scotland, the Netherlands and Sweden [1].Major upsurges are thought to be associated with substantive changes in market supply: during this time, eggs were imported from producers in EU Member States where there was a lack of vaccination of layer flocks against Salmonella or controlled food industry assurance schemes were not in place [1,10,11].From 2000 to 2008, the mean incidence rate for S. Enteritidis PT 14b NxCp L gradually increased from 0.01 per 100,000 population in England to 0.4 per 100,000 population, respectively.In 2009, this rate more than doubled, to 1.1 per 100,000 population (HPA unpublished data).This evidence, along with the findings of the 16 foodborne outbreaks, was used to formulate a hypothesis that S. Enteritidis PT 14b NxCp L infection of cases who were not part of the outbreaks was associated with consumption of eggs outside the home, within five days before symptom onset, particularly at restaurants serving Chinese or Thai cuisine.

Methods
A unmatched case-control study was carried out to analyse the apparently sporadic cases, recruiting two controls per case, to determine associations between potential risk exposures and symptomatic infection with S. Enteritidis PT 14b NxCp L .Cases from the 16 food-borne outbreaks were excluded from our study.
Sample size calculations indicated that having data for 60 cases and 120 controls would enable us to detect an odds ratio of 3 (for 50% of the controls exposed) to 4 (for 10% of the controls exposed) as being significant at the 5% level with around 90% power.

Case definition
A case of S. Enteritidis PT 14b NxCp L infection was defined as a person in England with abdominal symptoms (diarrhoea and/or vomiting), with an isolate from their stool sample positive for S. Enteritidis PT 14b with resistance to nalidixic acid and concomitant reduced susceptibility to ciprofloxacin, and the isolate received by the HPA Laboratory of Gastrointestinal Pathogens between 1 September and 31 December 2009.

Recruitment and investigation of cases
Recruitment of cases for the study took place between 1 October and 31 December 2009.Before the data collection period, 12 cases reported in September 2009 were reviewed using local authority food-poisoning questionnaires ('trawling' questionnaires) to assist in generating hypotheses for the possible source of infection.All cases interviewed with this questionnaire were excluded from the study.Cases associated with the 16 discrete food-borne outbreaks were also excluded from this study, as were cases who had travelled outside the United Kingdom within five days of symptom onset and cases who were contacts of other reported cases.
Standardised data were collected on all patients infected with Salmonella (i.e.before the serotype/subtype was known), so that cases and outbreaks could be identified and investigated rapidly.This involved the completion of a standardised questionnaire for each person with presumptive S. Enteritidis or laboratoryconfirmed Salmonella infection (all serotypes) by the Health Protection Unit or local authority.The extensive questionnaire included captured data on basic demographics, occupation, details of gastrointestinal illness and any other symptoms, history of travel, and details of food consumption and contact with animals within the five days before symptom onset.Questions on food consumption gathered details of the type and brand of each food consumed, place of purchase, whether the food was consumed in or away from the home, and type of food-service premises visited.The completed questionnaires were sent to the HPA Department of Gastrointestinal, Emerging and Zoonotic Infections for data entry, validation and analysis.Isolates were sent to the Salmonella Reference Unit at the HPA Centre for Infections for further characterisation and antimicrobial susceptibility testing [12,13].

Recruitment and investigation of controls
We used cases' landline telephone numbers, which reflect the location of their domicile, as the basis of the selection of controls (cases who had been contacted by mobile telephone were asked for a landline number).For each case, two controls were recruited using random digit dialling [14].Controls were therefore chosen from the same telephone exchange area and therefore lived in the same geographical area as the cases.Between 2 October and 2 December 2009, controls were recruited by telephone over five weekday evenings.The individual who picked up the telephone and who agreed to be interviewed was considered to be a control provided they were over the age of 18 years and they provided informed consent on the telephone before the interview.
All interviews were carried out using a standardised questionnaire for controls.This was similar to that used for cases, except that questions on contact with animals, travel history, food consumption and groceryshopping habits related to the five days before the interview (rather than before symptom onset).Controls who had experienced any gastrointestinal symptoms in the two weeks before the interview were excluded from the study.

Data analysis
The data were analysed using STATA 11.For all exposures, estimated odds ratios and 95% confidence intervals were used as measures of association.In addition, all exposures were tested, singly, for association with the outcome variable (illness) using chisquare test or Fisher's exact test.Exposures exhibiting some evidence of an association (p<0.2) were deemed eligible for inclusion in the multivariable analysis.The p<0.2 cut-off was chosen so that important exposures would not be missed due to confounding effects.A logistic regression model was constructed using a forward selection procedure including the most significant exposure at each step (likelihood ratio test p≤0.05).Potential confounding variables -age and sex -were included in the multivariable analysis regardless of statistical significance.

Results
A total of 489 S. Enteritidis PT 14b NxCp L cases distributed across all regions of England were identified by the HPA Laboratory of Gastrointestinal Pathogens during the study period.Of these, 101 were associated with the discrete food-borne outbreaks and were therefore excluded.Some cases not associated with these discrete outbreaks were also not included because they were interviewed with the initial trawling questionnaire in September, before the investigation, and others were excluded because they were identified after our investigation had closed.In total, 81 sporadic cases of S. Enteritidis PT 14b NxCp L infection completed the questionnaire.Of these 81 cases, 63 were included in the analysis: four were excluded due to recent travel history and 14 were excluded because they were contacts of other cases (although the index cases were included).There were reports of people with S. Enteritidis PT 14b NxCp L infection after December 2009, but the number reported had fallen to background levels.
A total of 108 controls were recruited: a mean of 3.6 calls (range: 1-32 calls) was needed to successfully recruit a control.Table 1 compares the basic demographic characteristics of cases and controls.Controls were more likely to be female (p=0.004)and older (mean age: 52.5 versus 36.8 years, respectively, compared with cases, p<0.0001).Due to these differences between cases and controls, single variable analysis was performed using logistic regression analysis adjusting for potential confounding by age and sex.
The cases had dates of symptom onset between 26 August and 16 November 2009, and the mean duration of illness in those who had recovered was 7 days (median: 7 days; lower and upper quartiles: 3 and 10 days, respectively).The predominant symptoms were diarrhoea (in 59 of 60 cases), abdominal pain (49 of 56), fever, defined as body temperature of at least 38 °C (32 of 55), nausea (29 of 55), headaches (26 of 55) and vomiting (20 of 59).Of the 63 cases, 15 reported having blood in their stool.A total of 50 visited their general practitioner, while 13 attended hospital accident and emergency departments and 12 were admitted to hospital.No deaths were reported among the study cases.
As there could be a delay in reporting (i.e.date of symptom onset was not necessarily the date the cases were reported) and to allow time for isolates to be sent for typing, the cut-off date for receipt of isolates at the HPA Laboratory of Gastrointestinal Pathogens was 31 December 2009.
In single variable analysis there was an association between having eaten away from home and symptomatic infection with S. Enteritidis PT 14b NxCp L , particularly in restaurants serving Chinese or Thai cuisine and kebab houses (Table 2).Having eaten barbecued foods either at home or away from home, and pre-prepared sandwiches obtained away from home, was also associated with a higher risk of becoming a case.There was a very strong association between having eaten eggs away from home and becoming a case (Table 2).
As both eating away from home at any type of establishment and eating foods from restaurants serving Chinese or Thai cuisine were found to be significantly associated with being a case, a three-level factor was generated to determine any association between being a case and (1) not eating out, (2) eating out at restaurants serving Chinese or Thai cuisine, and (3) eating out at other restaurants.The final multivariable logistic regression model including the implicated exposure variables (Table 3) demonstrated no significant association between having eaten away from home but not at restaurants serving Chinese or Thai cuisine and becoming a case.However, having eaten foods from restaurants serving Chinese or Thai cuisine (including takeaways) was significantly associated with becoming a case.Among food exposures, eggs eaten away from home and vegetarian foods eaten away from home were also identified as significant risk factors for becoming a case.

Discussion and conclusion
The case-control study presented here provides evidence of significant associations between eating in restaurants serving Chinese or Thai cuisine and eating eggs and vegetarian food away from home with becoming a case of S. Enteritidis PT14b NxCp L infection in a large national outbreak in England in 2009.The association between eating vegetarian foods and becoming a case may be related to the fact that vegetarian foods may contain eggs (which could be infected).These findings corroborated evidence obtained from concurrent investigations of 16 local discrete food-borne outbreaks of S. Enteritidis PT14b NxCp L infection.Our results indicated that the source of infection for the sporadic cases was likely to be the same as that for cases associated with the outbreaks.Information on eggs collected from food-service premises in seven of the 16 outbreaks indicated a common origin (a single production establishment in Spain).S. Enteritidis PT14 NxCp L obtained from eggs from this establishment, and also from environmental and food samples from the food-service premises were indistinguishable by molecular diagnostic testing from isolates obtained from human cases of S. Enteritidis PT14 NxCp L infection (cases associated with the outbreaks and the sporadic cases).S. Enteritidis PT1 NxCp L was additionally detected in eggs produced by this establishment in Spain as part of the outbreak investigations [15] providing further evidence of S. Enteritidis contamination within the laying flock.

Control measures
The United Kingdom Food Standards Agency was informed of the findings both from the case-control study and the 16  A decreasing trend in the notification rate of salmonellosis cases in the EU, particularly those caused by S. Enteritidis, has been seen over recent years.This has largely been attributed to the implementation of Salmonella national control programmes in the laying flocks [17].Nevertheless, most of the reported foodborne outbreaks reported in the EU are still caused by Salmonella, with the most important food source being eggs and egg products [17].Eggs have continued to be implicated as a source of or vehicle for crosscontamination in outbreaks of salmonellosis chiefly associated with the food-service industry in the UK [5][6][7][8].Food-poisoning risks associated with eggs and egg dishes in the food-service industry, especially those serving Chinese cuisine, have included highrisk practices such as breaking, pooling and mixing shelled eggs [18,19].One Salmonella-contaminated egg is capable of contaminating the whole batch of raw shell egg mix, and large numbers of consumers may be exposed to this contaminated raw material.The risk is increased if the egg mix is stored in a warm kitchen for later use during the day, as this would allow growth of the pathogen.Cross-contamination through egg mix aerosolisation during whisking and transfer to utensils and food preparation areas is also of concern [19].The rates of Salmonella contamination have been linked to the origin of the eggs [20].The food-service sector and consumers still need to be aware of this continuing hazard and adopt appropriate control measures and follow advice provided by national food safety agencies, in order to reduce the risk of infection.

Study limitations
Our case-control study had a number of limitations.Firstly, because of the limited time and resources available to recruit the controls, the final number of controls was slightly below the required number, based on our sample-size calculation (108 recruited as opposed to 120).In some of our analyses, small numbers led to large confidence intervals Secondly, for the recruitment of controls we interviewed the person who answered the telephone (provided they were aged over 18 years), which may have introduced further bias, as we found that those who were most likely to answer were more likely to be older and also female.We did not use a method such as the 'last birthday' method (in which the adult in the household with the most recent birthday is requested for interview during the telephone call) -such an approach might help to increase variation in the demographics of the controls.However, we took measures to try to minimise response bias by varying the days of the week and the times that controls were telephoned.
To minimise any potential confounding by age and sex, these were adjusted for in the regression analysis.
Thirdly, recall bias was a potential problem, particularly for controls.When cases were interviewed, they were asked about their food consumption in the five days before becoming ill whereas controls were asked about their food consumption in the five days before the telephone interview.
Fourthly, the time period for recruitment of cases did not exactly mirror that for the recruitment of controls, as we recruited controls over five weekday evenings in October and December 2009, whereas cases were recruited over a continuous period throughout October and December 2009.
Finally, we recognise that there may have been further confounders relating to differences in occupation, socio-economic status and eating behaviours between cases and controls.We attempted to minimise these potential confounders by interviewing controls who were living in the same telephone exchange area as cases.We also note that cases were not over-representative of Chinese or Thai ethnic groups (data not shown), so this form of confounding is not relevant to our investigation.
Despite the limitations -most of which are common to case-control studies of outbreak investigations of gastrointestinal infection -the results of the study support our hypothesis.

Introduction
In some outbreaks of infectious gastroenteritis, emesis predominates.The emetic syndrome is characterised by acute-onset nausea and vomiting.The most common pathogens associated with emetic syndrome are enterotoxin-producing Staphylococcus aureus and emetictoxin-producing Bacillus cereus [1][2][3][4][5].Staphylococcal food poisoning results from the ingestion of enterotoxins preformed in food by enterotoxigenic strains of coagulase-positive staphylococci, mainly S. aureus.
Several staphylococcal enterotoxins are heat-stable.
The range of the incubation period is 0.5 to 8 hours.B. cereus is a spore-forming microorganism, which can cause both emetic and diarrhoeal types of disease.It occurs ubiquitously in the environment (e.g. in soil) and may also be found in various foodstuffs.
The emetic type of disease is caused by a heat-stable peptide toxin (cereulide): the incubation period ranges from 0.5 to 6 hours.The illness usually does not persist longer than 24 hours but severe and fatal outcomes have been reported [6,7].The toxin is produced in food when the organism multiplies at ambient temperature for several hours (e.g. if the food is inadequately stored after cooking) [5].Emetic outbreaks due to B. cereus have mainly been linked to starchy foods such as rice, pasta and pastry [2].
Norovirus is also a common cause of outbreaks of acute gastroenteritis, with emesis as a prominent symptom.Infection can arise from contact with or airborne transmission from fomites, as well as faecal-oral and foodborne transmission.
Although outbreaks of acute gastroenteritis are notifiable in most countries, the number of toxin-related food poisoning outbreaks is largely underestimated because the disease is often mild and self-limiting, and laboratory detection (toxin testing) is not routinely performed.
On 3 December 2007, a kindergarten (A) reported cases of emesis among children and its personnel to the local health authority.In the morning of the same day they had been on an excursion on a local tram that included catering on the platform at the tram's final destination.Preliminary investigations by the local health authority confirmed the outbreak in this and two other participating kindergartens (B and C) from another Berlin district.
We conducted an investigation immediately after the outbreak had come to our attention, to assess its scope, to identify the causative agent, and to determine the risk factors and the vehicle of infection in order to prevent further outbreaks.

Case finding
The tram excursion took place on the morning of 3 December 2007 between 09:00 and 10:00.On the following day, cases among the kindergarten groups were identified by the local health authorities.On 6 December, we obtained the addresses and telephone numbers of the kindergartens from the local health authorities.Food safety authorities provided the address of the caterer and the list of food items served during the excursion.
Exploratory interviews at the kindergartens were conducted on 7 December and showed that the staff who had accompanied the excursion clearly remembered the relevant epidemiological details (e.g., disease status and food consumption) of the children.Therefore we interviewed the kindergarten personnel using a standardised questionnaire on the children's and their own clinical symptoms, time of disease onset, type and duration of symptoms, secondary spread among family members, food consumption and demographic data.

Case definition
We defined a case as a person who attended the excursion on 3 December 2007 between 09:00 and 10:00 and presented with vomiting, abdominal pain or diarrhoea within 24 hours after the excursion.

Cohort study
We conducted a retrospective cohort study among children and personnel of the three affected kindergartens.We described cases by date and time of disease onset.Age group-specific and kindergarten-specific attack rates were calculated.We also calculated food-specific attack rates, aetiological fractions, relative risks and 95% confidence intervals.Data were also stratified by kindergarten to compare the results between the kindergartens.We used EpiData for data entry and SPSS software, version 15.0, for statistical analysis.

Human samples
Stool samples (n=10) and one available vomit sample were tested (at the Institute for Food Safety, Drugs and Animal Health) for various enteric pathogens (Salmonella, Campylobacter, Escherichia coli and other enterobacteria, Yersinia enterocolitica, S. aureus, B. cereus and viruses such as norovirus, adenovirus, rotavirus and astrovirus).For detection of bacteria, routine culture methods were used, and for viruses, PCR and antigen tests were carried out.In the routine laboratory investigations of the stool and vomit samples, no tests for staphylococcal enterotoxins or B. cereus emetic toxin were performed.
An isolate of presumptive B. cereus from the vomit sample was tested for B. cereus cereulide production using liquid chromatography-tandem mass spectrometry (LC-MS/MS), and for the presence of the cereulide synthetase (ces) gene using PCR.For species differentiation, we used Fourier transform infrared spectroscopy [8].
For LC-MS/MS analysis of cereulide, bacteria were directly extracted with methanol during ultrasonification [8].Chromatographic separation took place on a C8 column with a buffer/methanol gradient, a triple quadrupole mass spectrometer with positive electrospray ionisation run in multiple reaction monitoring mode (mass-to-charge ratio 1,170.as described by Fricker et al. [9].For more details, see Rau et al. [8].

Food leftovers
Two unopened tetrapaks of the rice pudding that had been used, and retain samples (obtained from the caterer) of spray cream, cinnamon-sugar mix, gingerbread and two opened bags of cocoa powder were tested for Salmonella, staphylococci, B. cereus, Campylobacter, E. coli, Listeria monocytogenes, Clostridium perfringens, Enterobacteriaceae, Pseudomonas and norovirus.Leftovers of heated rice pudding eaten on the tram platform were not available for testing.

Environmental investigation
Local health and food safety authorities inspected the caterer's facilities used on the tram platform and the cleaning facilities in the caterer's office.The caterer was interviewed regarding food purchase, transport and storage, the facilities on the tram platform during the excursion (stand, water and electricity supply), the preparation process of food items and drinks served during the excursions, and on the cleaning procedures of the cookware.

Descriptive epidemiology
Overall, 155 persons (137 children, 17 kindergarten staff and one of the children's mother) from the three kindergartens participated in the excursion.The cohort characteristics are shown in Table 1.In total, 46 participants (43 children aged two to six years, and three adults) met the case definition (attack rate: 30%).The attack rate was higher among the children than among the adults, and differed significantly by kindergarten (p<0.001).
The predominant symptoms were vomiting (n=39), and abdominal pain (n=29).Diarrhoea was reported only in one person.Nobody was hospitalised and all cases recovered within one day.There were no secondary cases among household members.
The food items served during the excursion (at 09:45) were ready-to-eat rice pudding (from one-litre tetrapacks) that was heated before serving (served with cinnamon-sugar mix), cocoa drinks with and without whipped cream, and gingerbread.According to the personnel in Kindergarten C, the only person who became ill in this kindergarten recalled having been served from a different pot than that used for the other participants from this kindergarten.The participants had no other common meals before or after the excursion.
In all cases, symptoms started within a few hours after the end of the excursion.Detailed information about the time (hour) of symptom onset was available for 35 cases.Onset of symptoms began in the first case on 3 December, 2.5 hours after the meal had been served (Figure).The median time between the meal and symptom onset (the median incubation period) was four hours.No cases had onset of symptoms later than eight hours after the meal.

Cohort study
Of the food items served during the excursion, only consumption of rice pudding was significantly associated with illness in the cohort study.The relative risk was infinite (Table 2) with p<0.001, and all cases could be explained by the consumption of rice pudding (aetiological fraction: 100%).After stratifying by kindergarten (Table 3), the consumption of rice pudding remained associated with disease.

Laboratory results
One vomit sample was provided on the day of symptom onset (3 December 2007); 10 stool samples were provided after 6 December.'Presumptive B. cereus' (collective name for B. cereus sensu strictu, B. thuringiensis and closely related bacilli), isolated from the culture of the vomit sample, was analysed by LC-MS/MS for cereulide production and for the presence of the ces gene by PCR: both analyses gave negative results [8].No cereulide could be detected in the vomit sample itself.The isolate, initially described as presumptive B. cereus, was identified as B. cereus sensu stricto (non-cereulide producing) by Fourier transform infrared spectroscopy.
All stool samples taken within a few days after symptom onset and all food samples were negative for all tested pathogens.

Environmental results
All food items had been purchased by the caterer at the end of November 2007 and had been stored in the boot of the caterer's car until 1 December 2007.One similar excursion had taken place on 1 December 2007, with the same tram and the same catering company, but no outbreak occurred.
On both excursions, pots in an electric water-bath were used to heat the rice pudding and to keep it warm on the tram platform.The caterer stated that after the meal of the first excursion (on 1 December), rice pudding remnants had been scraped out of the pots and the pots were cleaned superficially in a wash-hand basin in an improvised kitchen in the caterer's office.According to the caterer, no food leftovers were served on 3 December.On that day, since there were more participants than in the previous excursion, the caterer used three additional cooking pots to heat up the rice pudding.The electricity supply was temporarily interrupted (due to a blown fuse) during the food preparation on 3 December.

Discussion
There is strong epidemiological evidence that the vehicle of the outbreak was rice pudding served during the excursion on 3 December 2007: the narrow epidemic curve indicated a common source of infection.All cases of emetic syndrome could be explained by the consumption of rice pudding from some of the pots used, while other food items were not associated with illness.Unfortunately, only one vomit sample was available for testing: no leftovers of the rice pudding portions served were available.This substantially hampered the laboratory investigations and no causative agent could be unambiguously identified.However, the clinical characteristics of this outbreak -including the short incubation period (of only a few hours), vomiting as the main symptom and the short self-limiting course of the disease -are typical for B. cereus emetic toxins or S. aureus enterotoxin.The fact that rice pudding was the likely vehicle suggests that this outbreak was caused by B. cereus cereulide.Starchy food products, including rice dishes, have been described as typical vehicles in B. cereus toxin outbreaks [2,5,10].However, S. aureus cannot be ruled out as the responsible pathogen.In both scenarios of B. cereus or S. aureus having caused the outbreak, the food contamination must have occurred at least several hours before serving because this minimum time is required for pathogen multiplication or germination (in case of B. cereus) and for toxin production [2,5].It is very unlikely that the unopened commercial readyto-eat tetrapacks were contaminated: had they been, more outbreaks would have been expected, given the wide distribution of these products.Since the cinnamon-sugar mix was added to the rice pudding only  shortly before consumption it can be ruled out as the vehicle of the outbreak.
Unfortunately, in the initial microbiological investigations the human and food samples had not been tested specifically for the presence of B. cereus toxins and S. aureus enterotoxins.In such outbreaks, human and food samples should be obtained and tested in a timely manner, not only for the usual pathogens (bacteria and viruses) but also for the relevant toxins, using the appropriate tests.The B. cereus-like strain isolated from the only vomit sample tested negative for cereulide or the ces gene.However, it is conceivable that emetic-toxin-producing B. cereus strains as well as non-toxin-producing strains were present in the rice pudding, but could not be detected in the vomit sample.The presence of B. cereus in the vomit sample and the absence of this agent from the unopened package of rice pudding is consistent with a scenario of B. cereus spores (including toxin-producing and nontoxin-producing strains) having contaminated the rice pudding after the tetrapacks were opened.The spores may have germinated and multiplied in remnants of the rice pudding left in the pots during an inadequate cleaning and storage process between the first and second excursion.This scenario is supported by the fact that not all of the pots appear to have contained contaminated rice pudding.
The fact that children from three kindergartens participated in the excursion and were affected by emetic syndrome shortly afterwards (although with attack rates differing by kindergarten) clearly pointed to a common source related to the excursion.This epidemiological pattern narrowed the spectrum of causative agents to toxin-producing agents.This shift of focus when patients from more than one setting are affected is an important epidemiological practice that is not always appreciated.If only one kindergarten had been involved, the investigation would have needed to also examine potential earlier sources of exposure to other pathogens such as norovirus and rotavirus.In this outbreak, the epidemiological investigation started shortly after the outbreak had been detected and the kindergarten staff clearly remembered the few food items consumed by the children.However, in other outbreak investigations, if substantial time elapses between symptom onset and epidemiological data collection (e.g.standardised interviews) or if many different food items had been served recall bias may be a major problem.
Although the environmental investigations did not determine the source of the food contamination, it revealed several breaches in food hygiene regarding cleaning of the cooking pots between the first and second excursion, as well as incorrect holding times and temperatures of food.
The epidemiological findings in this outbreak are consistent with other published B. cereus-associated food-borne outbreaks [11,12].It should also be noted that food can be contaminated at the same time by different strains of presumptive B. cereus (B.cereus sensu stricto, B. thuringiensis, B. weihenstephanensis), which can be difficult to discern in some cases of food poisoning [13][14][15].Also contamination with mixed cultures of emetic and non-emetic B. cereus sensu stricto can occur that can only be revealed by the testing of several isolates [8].Detection of the B. cereus toxin as well as S. aureus enterotoxin in human and food samples is not straightforward and may require advanced methods in specialised laboratories [13][14][15].
Mobile caterers and persons responsible for such excursions should be aware of the potential risk of outbreaks caused by bacterial toxins.In order to prevent B. cereus spores from germinating and producing heatstable cereulide, caterers need to ensure that food leftovers are discarded or refrigerated at a temperature below 10 °C and, if stored, that they are reheated thoroughly (at least 65 °C) before consumption.
In presumed food-poisoning outbreaks, stool and vomit samples from a substantial number of patients as well as relevant food leftovers and their ingredients should be obtained and investigated, not only for pathogens but also for the relevant toxins by appropriate tests.If B. cereus is identified, it is useful to further analyse several isolates from the culture to identify toxin-producing B. cereus strains.
In the light of our study, we recommended using single-portion, ready-to-eat rice pudding packs during future kindergarten field trips.No further food-borne outbreaks related to such excursions were reported to the local health authorities.

Introduction
Each year, one of five World Health Organization (WHO) member states experiences some type of event (disease outbreak, environmental calamity, etc.) that threatens the health of its people [1].It has been suggested that two billion people worldwide face health threats because they are at risk of, or exposed to, public health crises.Thus, preparation, mitigation, response, and control of such crises are public health priorities [1].Nonetheless, decisions aimed at resolving them are often taken without the active participation of those responsible for the implementation of implicated programmes [2].
Spain has experienced several public health crises in recent years, some of which were solved rapidly and adequately, while others were not.The tardiness or failure to resolve some of them has lead to sustained outbreaks, difficult political situations, or inappropriate information by the press, and thus generated undue social alarm.Crises of public health require a rapid assessment of measures necessary for their resolution to accurately assign and manage resources [3].When confronted with a crisis, many politicians are often rather concerned with its public consequences instead of investigating its causes.In response, pressure is put on epidemiologists to find causes and implement control measures rapidly that can complicate the investigation of an event.
In Spain, in 2005, a study involving public health experts from all Spanish Autonomous Regions was conducted with the intention to establish criteria for good practice in the management of epidemics (infectious diseases or not) or other emerging crisis situations in public health.The study objectives were (i) to determine which events provoke the most frequent public health crises, (ii) to reach a consensus regarding the appropriate actions to be taken when responding to events with an impact on public health, and (iii) to provide recommendations for their management.

Methods
For the purpose of the study, a public health crisis was defined as an event or a related series of events that overwhelm the capacity of the public health services to maintain the health of a community [4].We identified events which had most often provoked health crises in Spain between 1999 and 2004 through expert consultation and a database search.

Study participants
A letter was sent to general directors of public health services in the 17 Autonomous Regions asking for information about the five largest or most frequent crises experienced in the study period.Furthermore, the Autonomous Regions and the National Epidemiological Centre (CNE, Centro Nacional de Epidemiología) were asked to nominate a technical expert for collaboration with the study leader to ensure reliable information and to achieve a consensus for actions at national level.

Database and other sources searched
Databases: Medline, Biblioteca Virtual en Salud (BVS), Scientific Electronic Library Online-(Scielo), Literatura Latinoamericana y del Caribe en Ciencias de la Salud (LILACS), Pan American Health Organization (PAHO) and the World Health Organization's library database (WHOLIS), Cochrane Library Plus and Embase.
Web pages: World Health Organization, Eurosurveillance, Morbidity and Mortality Weekly Report, Elsevier, and Scirus.Other: Google, Yahoo, Doyma Editors, online archives of important national newspapers (ABC, El Periódico de Catalunya, La Vanguardia, El País, El Mundo, Diario Médico), Informe Quiral [5], and other sources, such as Epidemiological Bulletins of the public health services of the Autonomous Regions.
Keywords used to identify crisis included: epidemic, outbreak, intoxication, foodborne disease, public health crisis, public health crisis management, heat wave, Prestige (the only oil-spill disaster in Spain during the study period), bovine spongiform encephalopathy (BSE) and mad cow disease.The selection of keywords was based on the most frequent crisis experienced by the 17 Autonomous Regions.

RAND/UCLA Appropriateness method
We implemented the RAND/UCLA Appropriateness method, which is based on scientific evidence and combines the Nominal Groups and Delphi techniques [6].

Nominal Group technique
According to the Nominal Group technique a group of experts discusses, and eliminates ideas to finally agree upon a prioritised list of ideas [7,8].Our Nominal Group consisted of 17 experts responsible for epidemiological surveillance of epidemic outbreaks of transmissible and non-transmissible diseases in each of the respective Autonomous Regions and one expert from the CNE.In addition, the study coordinator and study leader were part of the group with a voting right.Consensus was considered as an agreement of at least 60% among the expert group members in line with the methodology described by Amezcua et al. [9].

Delphi qualitative evaluation technique
To reach a consensus on the most suitable actions for crisis management, the Delphi qualitative evaluation technique was considered as the most appropriate method [9,10].This technique consists of interviewing a group of experts or panellists using a series of questionnaires to identify future topics of interest.In our study, experts participated in a series of interactive sessions, organised in rounds to eventually create a high level of consensus.The panellists were the same experts as in the initial Nominal Group and all participated in each round.
Based on the panellists' answers to the initial questionnaire, a new questionnaire was created for a second round.The order of items presented was based on the percentage of agreement achieved in the first round.The questionnaire was then sent to the panellists with a request to arrange the items numerically by order of perceived priority and a coincidence of at least 60% was considered a consensus [7].After that, a final consensus list was created for the items for which consensus had been reached.
Email was used for the communication between panellists and the study leader for sending and receiving the questionnaires for each round, and for queries or feedback.In addition, telephone calls were used for clarification of remaining doubts.The role of the study coordinator was to supervise the work of the panellists and the study leader and to organise the meeting of the Nominal Group together with the latter.

Results
According to the representatives of the Autonomous Regions the most frequent diseases or events leading to public health crises involved outbreaks of legionellosis, foodborne diseases, SARS, BSE, bioterrorism, meningococcal meningitis, drinking water contamination (either by infectious pathogens such as norovirus, Shighella, and Cryptosporidium or toxins such as arsenic and lead), tuberculosis, and heat waves (Table 1).According to the results, 75% of the diseases or events provoking crisis in public health were of infectious aetiology, while 25% were due to other causes.
Our results show that events that cause or trigger public health crises vary considerably and that different bibliographic search strategies generate different results (Table 2).
The  The factors which influence the development of a public health crisis according to the panellists in the first round are listed in Table 3.In the second round, the factors which influence in order of priority were: (i) the type of disease or risk, (ii) social alarm generated and the population's perception, (iii) the population affected, (iv) measures taken by public health authorities, and (v) attitudes of the mass media (Table 4).
Participants agreed on a number of points that are relevant for a fast resolution of public health crisis: correct information, adequate qualification of technical personnel, availability of standardised protocols for investigation and control, availability of channels for case notification, communication between surveillance experts and healthcare services and evaluation of progress during resolution and of the final outcome.However, delay in starting an investigation, lack of coordination, disagreement between experts and politicians, lack of resources, and lack good communication were seen as hindering crisis resolution (Table 5).

Discussion
Our findings and the resulting recommendations which are drawn from Spanish public health experts' consensus could be of particular interest to public health authorities and politicians involved in the management of epidemics or public health crises caused by both communicable and non-communicable diseases.Literature research did not reveal similar exercises attempting to reach consensus for recommendations on how to deal with public health crises.Thus the lack of comparison with similar research represents a limitation of our work.The selected keywords were based on the most frequent crises experienced by the 17 Autonomous Regions.This may have lead to an overrepresentation of the incidents included.However, we believe that the results are valid and can be generalised for the Spanish context because of our intensive literature research.Furthermore, our nominal group included 17 experts from all Autonomous Regions in Spain and one expert from the National Epidemiological Centre.
The Delphi technique is used to reach consensus in large population groups that cannot meet regularly, or when the consensus pertains to a sensitive topic that cannot be debated publicly [11].We used the technique in our study considering the distance separating the panellists and the difficulty associated with face to face meetings of the Nominal Group.By combining two techniques (RAND/UCLA Appropriateness method) [6] however, it was possible for the experts to meet and discuss the proposals in a structured manner, and for us to facilitate consensus between disparate perspectives [9,10].
Early detection of an event that can lead to a crisis depends on standardised information systems available for health departments and clinical services to facilitate data management, investigation, and preparation of necessary responses [12,13].A lack of coordination between departments and ministries concerned with their 'own interests' can aggravate a crisis [14].
Management of crisis situations consists of three recognised stages: prevention, preparation of measures to be implemented, and recovery [15].Thus directors of public health authorities should estimate the impact of emergency situations, set up and implement appropriate actions, be persuasive, and employ organised management [16].During an emergency situation, preparation and adequate operational capacity are fundamental for a rapid and appropriate response by the public health system [17,18].For future improvement it is important to learn from the mistakes and successes of crisis response [19].In our study, experts considered measures taken by the health authorities a priority for resolving public health crisis.
Recommendations for the management of public health crises resulting from our expert group consensus are as follows: • To mitigate factors involved in crisis situations, it is necessary to create in advance guidelines with standardised protocols for investigation and control.• For a better implementation of prevention and control measures and an appropriate response when facing a public health crisis, the coordination between public health departments and clinical services needs to be improved.• Health policy must establish priorities and directions which ensure the effectiveness and efficiency of interventions.
In conclusion, our study shows that a considerable number of public health crises in Spain involve infectious diseases and that various factors contribute to the occurrence or aggravation of such situations.However, backed up by the literature reviewed and the consensus in the group of senior experts, we believe that public health crises can be mitigated or contained by adequate management following consensus documents that take these factors into account.Public health crises management can be effective if: the information among parties involved (public health experts and clinicians) as well as between these parties and the media is correct, the qualification of technical personnel is adequate, standardised protocols for investigation and control are available, evaluation of progress during the public health crisis resolution and of the final outcome is performed and, finally, if responsibilities are specified and well understood.[2] and national estimates, to evaluate on the one hand whether pooling indeed provides more robust estimates, and on the other hand, to explore potential geographical variation in such estimates.
In the Netherlands, we have been estimating effectiveness of the influenza vaccine in preventing medically attended laboratory-confirmed influenza-like illness (ILI) using the test-negative case-control approach for several years.While incorporating this in the routine ILI/influenza surveillance in primary care limits the possibility to optimise the design, to avoid bias, and to adjust for potential confounding, it ensures sustainability and assessment of annual variation.Unfortunately, our limited sample sizes do not allow strain-specific estimates, result in large confidence intervals, and make adjustment for age and underlying conditions challenging.Therefore, to increase power and obtain more valid VE estimates, we very much support pooled European analysis [2].
We estimated the VE using logistic regression on all medically attended ILI patients in the sentinel surveillance system with disease onset between the week in which influenza virus was encountered for the first time in the season and the end of April, the following year.

Figure
FigureCases by hour of symptom onset, outbreak of emetic syndrome following kindergarten excursion, Berlin, Germany, 3 December 2007 (n=35)

Table 1
Demographic characteristics of sporadic cases of L : resistance to nalidixic acid and concomitant reduced susceptibility to ciprofloxacin; PT: phage type.

Table 2
Single variable analysis of exposure variables for cases of Salmonella Enteritidis PT 14b NxCp L infection (n=63) and controls (n=108), adjusted for age and sex, England, October-December 2009 The reference category for each exposure is having not eaten at the specified establishment or having not eaten the specified food, or having had the relevant environmental exposure.
L : resistance to nalidixic acid and concomitant reduced susceptibility to ciprofloxacin; PT: phage type.a b Occupational contact or contact with pets.

Table 1
Cohort characteristics with attack rates, outbreak of emetic syndrome following kindergarten excursion, Berlin, Germany, December 2007

Table 3
Stratified analysis by kindergarten for rice pudding-specific attack rates, aetiological fraction and relative risks, outbreak of emetic syndrome following kindergarten excursion, Berlin, Germany, December 2007

Table 2
Food-specific attack rates, aetiological fraction and relative risks with 95% confidence intervals, outbreak of emetic syndrome following kindergarten excursion, Berlin, Germany, December 2007

Table 1
Most frequent events/diseases provoking public health crises according to responses from senior public health experts from Autonomous Regions, Spain 2005 aEither by infectious pathogens such as norovirus, Shighella, and Cryptosporidium or toxins such as arsenic, and lead.bNosocomialinfection.cTheonly oil-spill disaster in Spain during the study period.d Benign or malignant, due to proximity to magnetic fields.

Table 2
Literature research on reported causes of public health crises from 1999-2004 by source, Spain 2005 Google, Yahoo, Doyma Editors, newpapers (ABC, El Periódico de Catalunya, La Vanguardia, El País, El Mundo and Diario Médico) and Epidemiological Bulletins.
AIDS: Acquired immunodeficiency syndrome; BSE: Bovine spongiform encephalopathy; SARS: Severe acute respiratory syndrome.a b The only oil-spill disaster in Spain during the study period.c Nosocomial infection.d Particularly obesity.e Benign or malignant, due to proximity to magnetic fields.f Chickenpox, hepatitis B, chemical poisoning etc.

Table 3
Factors influencing the occurrence of public health crises, according to senior public health experts from Autonomous Regions (questionnaire first round), Spain 2005 a Discordant opinion, lack of coordination, new or limited knowledge of disease, outstanding relevance internationally.

Table 5
Consensus about appropriate actions for the resolution of public health crises, according to senior public health experts from Autonomous Regions, Spain 2005 a Disagreement between experts and politicians in decision takingLack of technical or economic resourcesLack of knowledge about the related topics Lack of good communication methods with de means; information excessively technical, lacking transparency, or contradictory a In order of priority: highest priority on top, lowest on bottom.

Table 4
Factors influencing the occurrence of public health crises, according to senior public health experts from Autonomous Regions (questionnaire second round), Spain 2005
A Steens

1 , W van der Hoek (Wim.van.der.Hoek@rivm.nl) 1 , F Dijkstra 1 , M van der Sande 1
1. Epidemiology and Surveillance Unit, Centre for Infectious Disease Control, National institute for Public Health and the Environment, Bilthoven, the Netherlands Citation style for this article: Steens A, van der Hoek W, Dijkstra F, van der Sande M. Influenza vaccine effectiveness, 2010/11.Euro Surveill.2011;16(15):pii=19843.Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=19843 Article published on 14 April 2011 To the editor: The editorial [1] and the articles related to it published on 17 March 2011 in Eurosurveillance provide important information on preliminary midseason influenza vaccine effectiveness (VE) estimates for the 2010/11 season.Reliable VE estimates are essential for effective communication and planning of scarce resources.It is important to assess concordance between pooled European data For the current season, we included cases up to 21 March 2011.For 2009/10 and 2010/11, we excluded cases if the period between disease onset and date of swabbing was greater than seven days.The crude effectiveness of the trivalent seasonal influenza vaccine in 2006/07, 2007/08[3], 2008/09[4], and of the monovalent 2009 influenza A(H1N1) pandemic vaccine in 2009/10 ranged from 20% to 60%.Adjustment for age lowered the VE estimates and widened the confidence intervals (Table).The crude VE estimate for the 2010/11 vaccine was 46% (95% confidence interval: 9-67), which is similar to what has been reported in other European studies[2].The 2010/11 VE estimate was lower when only individuals with an indication for vaccination (underlying condition or aged 60 years or older) were included.It is worrying that patterns similar to those observed in the Netherlands are observed on a European scale.In particular, the consistent pattern of reduced VE estimates following correction for potential confounding by age or underlying conditions warrant further studies to develop methodologies for robust, non-biased VE estimates.