Health Stream Literature Summary - Issue 56 - December 2009

A hepatitis E outbreak caused by a temporary interruption in a municipal water treatment system, Baripada, Orissa, India, 2004
Swain, S.K., Baral, P., Hutin, Y.J., Rao, T.V., Murhekar, M. and Gupte, M.D. (2009) Transactions of the Royal Society of Tropical Medicine and Hygiene. doi:10.1016/j.trstmh.2009.07.020

Hepatitis E is an acute disease which affects mostly young adults and has a high case fatality ratio among pregnant women in the third trimester. Hepatitis E virus (HEV) causes large outbreaks in developing countries and among displaced populations living under poor sanitary conditions due to transmission through the faecal-oral route. Outbreaks of hepatitis E have been reported in India for a number of years in Delhi, Kanpur and recently in Hyderabad. A cluster of acute jaundice cases in Baripada, a rapidly growing urban settlement, in the state of Orissa, India was identified in the third week of January 2004. The municipality is supplied with water by a municipal supply system with water from a number of sources. The cases were clustered in one particular ward (administrative area) of the city. A rapid task force was deployed to investigate the outbreak.

A case was defined as the onset of fever with acute jaundice in a resident of Baripada between January and February 2004. Cases were actively searched for in the entire area of the municipality. On the basis of findings from descriptive epidemiology, one of the water sources of the municipal water system was suspected to be the source of the outbreak. A case-control study was then conducted which included all cases found and an equal number of control subjects who were selected randomly from the houses without any case patient. Case patients and controls were interviewed about potential exposures in January 2004, including source of drinking water, sharing a community feast, consuming food in a common restaurant or from a food vendor. Blood specimens were collected from a random sample of case patients to test for viral hepatitis, including detection of IgM antibodies to the hepatitis A virus (HAV), to the core antigen of the hepatitis B virus (IgM anti-HBc) and to HEV (IgM anti-HEV). Twenty-five water specimens were examined to estimate turbidity, count presumptive coliforms and measure available free residual chlorine. All sources of water supply in the city were inspected. Information was also collected regarding the procedures used to treat drinking water supplied to the community.

The case search identified 538 cases and 5 deaths (attack rate: 5.1 per 1000 population, case fatality rate: 0.93%). There was a variation in attack rate according to neighbourhoods, with a cluster in one particular part of town which accounted for 378 (70%) of all cases. The five most affected wards had a common water source pumped from the nearby Chipat river, other neighbourhoods received groundwater. There were 538 controls selected for the case-control study. Cases were found to be more likely to consume water that came from the Chipat river (91% vs 30%, stratified odds ratio 31, 95% CI 27-48). There were 48 serum specimens that could be tested for markers of viral hepatitis and of these 47 were positive for IgM anti-HEV and all were negative for anti-HAV IgM, HBsAg and anti-HBC IgM. One serum specimen was found to be positive for anti-HAV IgM.

Water for the city was usually treated using flocculation, sedimentation, graded filtration and chlorination. However between 2 and 10 January 2004, a strike by public health engineering department pipeline workers resulted in water treatment activities being interrupted for all water source supplies. At the time of the strike, the population from the affected area had complained of turbid water. However when the investigation was conducted 57 days following the strike, the 25 water samples were satisfactory in terms of presumptive coliforms counts, turbidity and free residual chlorine level. The river received sewage discharges from upstream although no specific contamination source leading to this outbreak was identified.

This large outbreak of hepatitis E is the first documented occurrence of hepatitis E in the Indian state of Orissa. The pattern of the outbreak, the results from the case-control study, the laboratory and environmental investigations all support the suggestion that the water supply originating from the river was the source of the outbreak. However the investigation was limited by the time lag between the water treatment interruption and recognition of the outbreak (due in part to the incubation period of the disease). The information gathered here was used to develop prospective contingency plans for the maintenance of basic essential services for the provision of safe water supply in case of unusual events, including strikes. Further studies are required to evaluate the effectiveness of the various water treatment steps against HEV.

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