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Eurosurveillance, Volume 4, Issue 10, 01 October 1999
Outbreak report
Investigation of an outbreak of amœbiasis in Georgia

Citation style for this article: Kreidl P, Imnadze P, Baidoshvili L, Greco D. Investigation of an outbreak of amœbiasis in Georgia. Euro Surveill. 1999;4(10):pii=40. Available online: http://www.eurosurveillance.org/ViewArticle.aspx?ArticleId=40
P Kreidl 1, P Imnadze 2, L Baidoshvili 2, D Greco 3
1 European Programme for Intervention Epidemiology Training (EPIET), Istituto Superiore di Sanità, Roma, Italy
2 National Centre for Disease Control, Tbilisi, Georgia
3 Laboratory of Epidemiology and Biostatistics, Istituto Superiore di Sanità, Roma, Italy

Entamoeba histolytica, a protozoan parasite, occurs worldwide and 12% of the world's population are estimated to be infected (1). The prevalence of infection varies between 1% in industrialised countries to between 50% and 80% in tropical countries, where transmission of E. histolytica cysts by untreated drinking water is common. Ingestion of food and drink contaminated with E. histolytica cysts from human faeces and direct faecal oral contact are the commonest means of infection (2,3), but outbreaks due to E. histolytica are rarely reported. Cyst carriers are the main reservoir for infection. Cysts may remain viable for three months but may be destroyed by hyperchlorination or iodination. The incubation period is usually two to four weeks but may be as long as months or years. About 10% of those infected have clinical symptoms. Most (80% to 98%) present with amoebic colitis, with diarrhoea and abdominal pain, the remaining 2% to 20% present with extra-intestinal disease, most commonly as liver abscess (4-6). The case fatality rates of E. histolytica liver abscess are estimated to be between 0.2% to 2% in adults and up to 26% in children (1). Metronidazole is the drug of choice for treatment of liver abscess and intestinal disease; cyst carriers should be treated with diloxanide furoate or iodoquinol.

On 27 August 1998, the Regional Office for Europe of the World Health Organization (WHO/EURO) asked the Istituto Superiore di Sanità (ISS) (the National Health Institute of Italy) for an immediate assessment of an increase in the incidence of amoebiasis in Georgia’s capital city, Tbilisi (population 1.7 million), which had been reported by the Georgian Minister of Health. The aim of the assessment was to describe the extent of the outbreak and to provide recommendations on control measures to be undertaken. A brief overview of the assessment is presented here.

Background

The collapse of the previous economic system and the civil war in 1993 have seriously impaired the social and health situation in Georgia. Data from the State Department of Statistics from 1996 estimated that a family of four needed a monthly minimum of 188 Laris (aroud 100 Euros) but the usual monthly minimum was only 43 Laris (around 20 Euros) per person working. In 1996, over 65% of the population were estimated to be below the poverty level, but this percentage is reported to have fallen in the past two years. Health services are free-of-charge only for emergency situations; otherwise, drug treatment and hospital care must be paid for by the patient.

Amoebiasis was a notifiable disease in Georgia until the early 1970s, but was subsequently dropped from the list, because only one to three cases were notified each year. Costs for diagnosis and treatment of amoebiasis were not covered by the primary health service. In July 1998 more than 10 probable cases of amoebic liver abscess were admitted to hospitals in Tbilisi. An emergency committee was set up by the Ministry of Health and arranged for diagnosis and treatment to be offered free of charge. The Georgian National Centre for Disease Control (GNCDC) asked hospital doctors and microbiologists to notify all suspected cases of amoebiasis, giving the age, sex, address, working place, and profession of patients, and the symptoms, their dates of onset, date of hospital admission, laboratory results, and treatment of the disease. In order to detect additional cases, active case ascertainment was carried out by the local health authorities at the end of July by conducting doorstep interviews in the neighbourhood where cases had already been identified. By 10 August, television broadcasts were advising the public to present at hospital if suffering from bloody or mucous diarrhoea or symptoms that could indicate liver abscess (for example, fever with upper abdominal pain).

Methods

Most of the information used for assessing the local situation was obtained by systematically reviewing local official records. During the assessment mission all the notifications received from July to the beginning of September were reviewed and cases of amoebiasis classified as follows:

- cases of intestinal amoebiasis; defined as people living in Tbilisi, affected by acute diarrhoea, diagnosed on the basis of positive microscopy for amoeba cysts or trophozoites in the stool;

- cases of probable amoebic liver abscess; defined as people living in Tbilisi diagnosed with a cystic lesion in any segment of the liver, either by ultrasound or computed tomography;

- cases of confirmed amoebic liver abscess; fulfilling the definition of a probable case but with detectable antibodies in a single serum specimen either by positive Latex agglutination performed at the GNCDC or by the polyclonal Entamoeba antibody enzyme linked immunosorbent assay (ELISA) (antibody titres >1:64) performed at the ISS.

Data on the size of the residing population by district were obtained through the GNCDC.

Maps of the water supply and sewerage system were obtained from the Water Sanitation Department (a government organisation). Information about the sources and treatment of drinking water was obtained from the municipality, the local private water supply company, and visits on site. Filtered drinking water samples taken from several previous affected areas at the beginning of September, after control measures had been taken at the filtration station by the local authorities, were tested using culture and polymerase chain reaction (PCR) at the ISS. Logistic constraints prevented us from conducting an analytical study during this assessment.

Results

Description of the epidemic

One hundred and seventy-seven cases of amoebiasis were reported to the GNCDC, between 26 May and 3 September 1998, including 71 cases of intestinal amoebiasis and 106 probable cases of liver abscess. This was equivalent to a cumulative attack rate of 10.4/100 000 population in the city. Only six of the cases were found by the active door to door case ascertainment exercise in July 1998.

Thirty-eight probable cases of liver abscess underwent microbiological investigation, 34 of whom were confirmed by either latex agglutination or ELISA (table).

Table: Laboratory results among cases of amoebiasis between 26 May and 3 September 1998, Tbilisi, Georgia

 

Total

Tested

Positive

Latex

ELISA

Total

Latex (%)

ELISA (%)

Total

Probable cases of liver abscess

106

18

22

39*

17 (94)

18 (82)

34 (90)*

Cases of intestinal amoebiasis

71

-

9

9

-

7 (78)

7 (78)

Total

177

18

31

48*

17

25 (81)

41 (87)*

* One patient was tested with Latex and ELISA.

The epidemic curve had no distinct peak (figure) but the largest number of cases developed symptoms in early August. The incidence of cases has decreased since mid September.

fig2.gif (49760 octets)

 

Ninety-one per cent (161) of cases of amoebiasis lived on the left side of the River Kura, and cases who did not live there worked in this area. Attack rates by district of Tbilisi ranged between 3 and 42 per 100 000 inhabitants. The highest attack rates were close to a water filtration system that used surface water from a large lake and all districts with attack rates exceeding 15/100 000 were fed by this source. At this water treatment works the filters were of poor quality and routine maintenance was not documented. Districts with lower attack rates were fed by ground water.

In Tbilisi as a whole, between 600 and 700 breakdowns of the water supply and sewerage system were reported between April and September 1998, but the routine Escherichia coli index in drinking water, investigated by two different laboratories, was never reported to be significantly increased. No previous problems with the water treatment works had been reported. All water samples investigated at the ISS were negative for cysts.

The mean age of probable and confirmed cases with liver abscess was 49 years (median 47, range 7-79). Eighty four per cent (88/106) of them were males, and 30% (19/63) of cases with liver abcess and of whom information were available (63) did not report previous abdominal symptoms. All patients with liver abscess were admitted to hospital and treated with intravenous metronidazole for three days, followed by oral metronidazole and doxycycline for 11 days. Four patients with liver abscess died (case fatality rate 3.8%).

Cases of intestinal amoebiasis were nearly equally distributed between the sexes and their mean age was 41 years (median 42, range 3-79). Patients with severe intestinal disease were treated in the same way as those with liver abscess but patients with mild intestinal disease were treated with oral metronidazole. Chloroquine was given for 20 days to eliminate carriage of cysts. No other drug for treatment of cyst carriers was licensed in Georgia.

Interventions

Since 10 August the public has been advised to boil tap water before drinking, although routine tests for E. coli in the water never showed significant elevation. On 23 August, control measures were taken at the water filtration station. The dosage of aluminium sulphate for coagulation was increased, residual chlorine was increased from 0.3% to 0.7% before filtration, the duration of back washing was increased, filters were thoroughly cleaned, and the filtration speed was reduced. The second chlorination, performed after the water treatment works and before the water is distributed to the pipe system, was also increased. At the end of August, Russian hydrobiology experts were invited to investigate the different sources of drinking water supply, but no cysts of E. histolytica were detected. The number of cases has decreased since September, but the incidence has not fallen to zero.

Discussion

Descriptive epidemiology is the major tool for an assessment and in the current outbreak it was suitable to formulate the most likely hypothesis about transmission. The unusually high incidence of cases of amoebiasis and their geographical distribution suggested a waterborne outbreak from a common source. The local situation in Georgia did not allow an epidemiological analytical study to be performed during the assessment.

Our hypothesis is that either faecal contamination had happened after the water treatment works or the filtration process had been inadequate. The second chlorination could have made the levels of other pathogens so low as to be undetectable. The high proportion of cases presenting with liver abscess suggests either that the strain was very invasive or that the population was very susceptible. Cases with intestinal disease are likely to have been grossly underreported before medical care was offered free of charge and the public was informed.

Other sources of infection, such as food and drink and transmission by flies, were considered by local authorities but are unlikely to have been responsible for the outbreak. Ensuring quality standards in the drinking water and sewerage systems is crucial to prevent continuing transmission and further outbreaks. Treatment processes should be applied rigorously and documented, and water quality monitored against standards if we are to minimise the risk of such large scale outbreaks.

Furthermore, clear protocols for plans of action must be formulated in the event that cases continue to occur or cysts continue to be detected in the drinking water supply. Meanwhile amoebiasis should be made notifiable and incidence of disease documented in the whole country. Screening facilities for asymptomatic carriers should be easily accessible to the public and carriers should be treated.

Further reports from the GNCDC have shown that the incidence has decreased but cases are still occurring in Tbilisi. The wide variation in incubation period will make it difficult to estimate the actual period of infection and, in addition, secondary cases are expected to occur. National notification data suggest that 1377 cases of intestinal amoebiasis and 365 cases of liver abscess arose in Tbisili between July 1998 and June 1999, and that numbers have declined since September 1998 (P Imnadze, director of GNCDC, personal communication). In June 1999, 35 cases of intestinal amoebiasis and 13 of liver abscesses were notified.

Analytical epidemiological studies, which have been carried out by the GNCDC and the Centers for Disease Control and Prevention, Atlanta since the assessment, may help to identify the risk factors in the continuing cases, and thus provide the information necessary to guide prevention.

It is unlikely that all problems related to the sewerage and drinking water systems will be solved in near future despite the efforts made by the local authorities. An increased risk of acquiring amoebiasis in Tbilisi may be present for several years and amoebiasis due to E. histolytica should be considered in travellers to Georgia.

Amoebiasis is rarely reported in western Europe and included in statutory notification systems in only six countries (Austria, Belgium, Luxembourg, Norway, Portugal, and Sweden) (7).

Acknowledgements:

We would like to thank all the people who contributed to this investigation, namely Gia Arbolishrili and Guliko Namoradze, Municipal Public Health Office, Eteri Botsvadze, Department of Infectious Diseases of the Medical University, Ramaz Urushadze, Department of Public Health, Merab Iosava, GNCDC, Nicholaz Shavdia, Michael Kurchuli, and David Gagua, State Sanitation Department, Iusa Tsartsidze, water supply company, Avtandil Jorbenadze and Amiran Gamkrelidze, Ministry of Health. Furthermore, we would like to thank Rusiko Klimiashiili for her support and translating, M. Scamiccia for serological and parasitological investigations, Marta Ciofi degli Atti, Olivier Ronveaux, Stefania Salmaso, Mike Rowland, and Alain Moren for their critical reviews.

* EPIET, a programme funded by DGV of the commission of European Communities.


References

1. Farthing MJ, Cevallos AM, Kelly P. Intestinal protozoa. In: Cook GC (editor). Manson's tropical diseases, 20th edition. London: WB Saunders Company, 1996: 1255-69.

2. Bruckner DA. Amebiasis. Clin Microbiol Rev 1992; 5: 356-69.

3. Markell EK, Voge M, John DT. Medical parasitology. Philadephelia: WB Saunders Co, 1986.

4. Benenson AS, (editor). Control of communicable diseases manual. 16th edition, Washington DC: American Public Health Association, 1995: 10-3.

5. Raudin JI, Petri WA. Entamoeba histolytica (amebiasis). In: Mandell GL, Douglas RG, Bennett JE (editors). Principles and practice of infectious diseases, 4th edition, Churchill Livingstone: New York: 1995: 2395-407.

6. Marshall MM, Naumovitz D, Ortega Y, Sterling CR. Waterborne protozoan pathogens. Clin Microbiol Rev 1997; 10: 67-85.

7. Salmaso S (editor): Inventory on communicable diseases in the European Union, Norway and Switzerland. Luxembourg: EC-DG V 1998



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