The millennium year 2000 brought 26 million visitors to Rome. The pilgrims
as a group were characterised by heterogeneous geographic origin (16.1
million from Italy, 5.3 from western Europe, 1.5 from eastern Europe,
0.9 from Asia, 0.7 from North America, 0.6 from South America, 0.1 each
from Africa and Oceania), short duration of stay (2.5 days), and congregation
in large crowds.
Mass gatherings are considered high risk for the spread of infectious
diseases (1-3). The surveillance of infectious diseases in the Lazio
region was enhanced through a laboratory based system with special attention
to diseases with high epidemic potential, high incidence, and short
incubation period, ie foodborne disease outbreaks (FBDO), and meningitis.
The European surveillance of legionnaires' disease provides information
on diseases diagnosed abroad. A rapid alert network was implemented
from hospital emergency departments (ED) and a group of general practitioners
committed to treating pilgrims. This paper reports the results of the
surveillance of these infectious diseases during the millennium year.
Since 1997, an integrated surveillance system involving statutory notification
and the reporting of positive laboratory tests has been functioning
in the Lazio region for the following pathogens: Salmonella, Campylobacter,
pathogenic Escherichia coli, Giardia, Neisseria meningitidis, Streptococcus
pneumoniae, Haemophilus influenzae, and Legionella pneumophila. For
legionnaires' disease, an additional surveillance has been active since
1997, in accordance with the protocol of the European Working Group
for Legionella Infections (EWGLI) (5). The principal sources of notifications,
ie hospitals, general practitioners, emergency wards, and laboratories,
participate in a rapid alert network for meningitidis and report probable
cases of targeted diseases and suspected outbreaks to local public health
services. Notification takes place immediately after diagnosis of suspected
meningitis or FBDO and within 48 hours of suspected legionnaires' disease.
In 1997 guidelines for epidemiological investigation during FBDOs were
introduced (6). A programme to control FBDOs was adopted during the
millennium year, involving the Millennium Food Safety Committee. It
included courses for public health workers about Hazard Analysis Critical
Control Points (HACCP) as applied to catering for large gatherings and
about epidemiological methods of conducting FBDO investigations. During
World Youth Day (WYD), the most important gathering with more than 1.5
million pilgrims, there was only one food provider and processes for
meal production had previously been agreed upon by the provider and
the Millennium Food Safety Committee. Pamphlets with recommendations
about safe food consumption and individual diarrhoea management were
given to pilgrims during WYD.
We used the case definitions recommended by the Centers for Disease
Control and Prevention (CDC) for the targeted diseases (7). Foreign
tourists are defined as persons without Italian citizenship and not
residing in Lazio (5.3 million inhabitants). During FBDO investigations,
pilgrims were defined as groups coming to Rome for the millennium from
any country. We compared the number of cases that occurred in 2000 (observed)
with the mean number of cases in 1998 and 1999 (expected) (O/E). We
considered the day of onset of symptoms as the date of incidence of
the disease. We analysed in detail the three months with the most important
gatherings: January (Epiphany, 6 January), April (Easter, 23 April),
and August (WYD, 14-20 August). We calculated 95% confidence intervals
(CI) of observed/expected ratios, assuming that both followed a Poisson
distribution. For the differences between mean ill persons per FBDO,
a t-distribution was used. We analysed the monthly frequency of visits
to emergency departments (EDs) for foreign tourists and residents separately.
There was an increasing trend in the number of cases and outbreaks of
these infectious diseases from 1995 to 1999 (Figure).
The number of FBDOs and of cases of bacterial/viral meningitis and legionnaires'
disease observed in the Lazio region did not increase in 2000 as had
been expected based on the figures for 1998-1999 (Table). The FBDOs
involving foreign tourists increased (O/E=3.5; 95% CI [0.9-16.3]). Cases
of legionnaires' disease among foreign tourists exposed in Lazio showed
an increase in 2000 (O/E=2.5; 95% CI [0.9-7.3]). The monthly average
number of visits for foreign tourists to EDs for abdominal pain and
intoxication was 167 with a peak (+75.9%) in August, while for residents
it was 8860 visits with a smaller increase (+18.2%) the same month.
A similar distribution of visits was reported for all causes of residents
(161 700 visits/month, +12.0% in August) and foreign tourists (2755
vistits/month, +90% in August). A similar distribution of visits was
reported for the accesses for all causes of residents (161 700 visits/month,
+12.0% in August) and foreign tourists (2755 visits/month, +90% in August).
The number of cases of these infectious diseases reported in January,
April and August 2000 is similar to the number reported in the same
months over the reference period, except for a peak of viral meningitis
in August 2000 (O/E=2.0; 95%CI [0.9-4.5]). The mean number of ill persons
per FBDO is larger in 2000 (difference 5.3; 95%CI [2.1-12.7]), due to
a few large events. During the millennium year, six FBDOs involving
groups of pilgrims, four among foreign tourists and two among Italians,
were reported. Religious guesthouses were the setting of three FBDOs.
The pathogens of FBDOs were mostly the same in the two periods: Salmonella,
Staphylococcus aureus, Clostridium perfringens and Clostridium botulinum,
as were the four most common food vehicles: sweets containing custard,
fish, meat, and mushrooms. The pathogens of bacterial meningitis are
mostly the same for the two periods: Streptococcus pneumoniae, Neisseria
meningitidis, Haemophilus influenzae, Streptococcus spp, Staphylococcus
spp, Listeria monocitogens, Escherichia coli, and Acinetobacter
The number of cases and outbreaks of the targeted infectious diseases
reported during the Millennium year among the residential population
was slightly lower than the mean of the two previous years for meningitis
and FBDOs, and slightly higher for Legionnaires' disease. The increasing
trend in reported cases and outbreaks from 1995 to 1999 could be interpreted
as an increase in surveillance sensitivity, which make us more confident
in the validity of the figures for 2000 (Figure). Moreover, data from
EDs are consistent with a good sensitivity of information gathered on
health problems among foreign tourists. No atypical etiological agents
in foodborne diseases or meningitis appeared. Similar results had been
reported during the Olympic Games (2-4). Cases of legionnaires' disease
reported by the international surveillance increased during the millennium
year. We also found an increase of FBDOs involving foreign tourists.
Thus, apart from the outbreaks and cases involving pilgrims or foreign
tourists, the presence of 26 million visitors during the millennium
year did not influence the epidemiology of these infectious diseases
in the residential population of Lazio. The increase in cases among
foreign tourists may not reflect an increase in incidence, but may instead
be simply explained by the increase in the number of foreign visitors.
The lack of data regarding the person-time spent by the visitors in
the previous years makes it impossible to answer this question.
During the millennium year, the average size of the FBDOs was larger;
this is attributable to a few large events. Religious guesthouses appeared
prominently among communities involved in food borne outbreaks. They
were used to house pilgrims, and their facilities had to prepare more
food thus increasing the risk of FBDOs.
The incidence of bacterial meningitis, FBDOs, and legionnaires' disease,
did not increase in January, April or August, the months with the largest
gatherings. The anomalous summer peak of viral meningitis in August
2000 may be the consequence of one or more undetected clusters.
Some methodological problems should be highlighted. The data used for
this study were limited only to two years: 1998 and 1999. This choice
is due to the willing exclusion of 1997, the year the surveillance system
was modified. Because of the brevity of the pilgrims' average stay in
our region (2.5 days), the onset of symptoms tended to occur after their
return to their countries of origin, especially in the case of viral
meningitis, which has a long incubation period (10-15 days). This phenomenon
is less relevant for FBDOs, because the incubation period is less than
three days; while for legionnaires' disease, the international surveillance
reports avoided losing cases diagnosed in other European countries.
Although this important event did not change the epidemiology of infectious
diseases for residential population, an increased number of cases of
legionnaires' disease and FBDOs among foreign tourists was reported
with a high proportion of the FBDOs in religious guesthouses.
We would like to thank Dr Guido Bertolaso, Deputy Commissary of the
2000 Jubilee, and Dr Mario Rastrelli, Health Director for the Jubile
2000 for their support in the implementation of infectious disease control
measures, the members of the Jubile Food Security Committee, Dr Paloa
Aureli, the Istituto Superiore di Sanità (Italian Public Health
National Institute), Dr Marco F.G. Jermini, the WHO European Centre
for Health and Environment, Pr Adriano Mantovani, the WHO-FAO collaborating
centre for vetenary public health and Pr Giovanni B. Quaglia, the national
Italian institute for reaserch on foods and nutrition for their contributions
in the courses for public health agents on the food security surveillance
and the revision of HACCP on food production during the WYD.