WATER-BORNE HEPATITIS-E VIRUS EPIDEMIC IN ISLAMABAD, PAKISTAN - A COMMON SOURCE OUTBREAK TRACED TO THE MALFUNCTION OF A MODERN WATER-TREATMENT PLANT

During December 1993 and in the first three months of 1994, an explosi ve water-borne epidemic of hepatitis E virus (HEV) occurred in two sec tors of Islamabad, Pakistan. In a survey of a population of 36,705 ind ividuals, a total of 3,827 cases of acute icteric hepatitis were recor ded with an overall attack rate (AR) of 10.4%. The etiologic role of H EV in the epidemic was proven by demonstrating anti-HEV IgG and HEV Ig M in the tested serum samples. The water-borne nature of the epidemic was suggested by a study of the case distribution according to water s upply. Prior to the epidemic, there had been an operational breakdown in a water treatment plant that distributed water to the affected area s while transforming its purification system from slow sand to rapid s and filtration. The primary source of water for the plant was derived from a heavily contaminated stream. The highest AR (16.3%) was observe d in the areas where the source of drinking water was exclusively from the purification plant, followed by ARs of 12.4% and 5.3% for those r eceiving 50% and 30% or less of their water supply from the treatment plant, respectively, while the lowest AR (1.8%) was observed in the ne ighboring areas that did not receive water from this source. The AR wa s significantly higher in the group 11-30 years of age (15.3%) as comp ared with children less than 11 years of age (1.4%) and also relative to the group greater than 30 years of age (10.5%). The AR among the 16 2 recorded pregnant females was 21.6%, which was higher than that foun d among nonpregnant females of child-bearing age (10.9%). All four rep orted adult deaths occurred among females in their third trimester of pregnancy with a case fatality rate of 11.4%, while the other four fat al cases were newborn infants of mothers with acute icteric hepatitis. Although the aggregation of cases within households was significantly related to family size, the temporal relationship between cases in ho useholds with two or more cases revealed that 83.7% of 1,463 presumed secondary cases occurred within one month of the first case in the sam e household, which is not suggestive of person-to-person transmission of disease. The termination of providing water from the source was eff ected, which was followed by an apparent decrease in cases.