CONTRASTING ROLES OF RIVERS AND WELLS AS SOURCES OF DRINKING-WATER ON ATTACK AND FATALITY RATES IN A HEPATITIS-E EPIDEMIC IN SOMALIA

In early 1988, an increased incidence of acute hepatitis was observed in villages along the Shebeli River in the Lower Shebeli region of Somalia. This was followed by a large epidemic that lasted until late 1989. In a survey of 142 villages with a population of 245,312 individuals, 11,413 icteric cases were recorded, of which 346 died, corresponding to an attack rate and a case fatality rate of 4.6% and 3.0%, respectively. The etiologic role of hepatitis E virus (HEV) in this epidemic was proven by demonstrating anti-HEV in 128 of 145 sampled cases as a sign of recent infection with HEV. In three villages, where a special study protocol was implemented, the attack rate was found to increase significantly with age from 5% in the group 1-4 years of age to 13% in the group 5-15 years of age and to 20% for persons older than 15 years of age. Among cases 20-39 years of age, the female-to-male ratio was 1.5:1, which was a significant predominance of females. As in other hepatitis E outbreaks, there was a high fatality rate in pregnant females, estimated to be 13.8%. The epidemic peaked with the rise in the level of the river during rainfall, suggesting that the disease was waterborne. The attack rate was higher (6.0%) in villages supplied with river water, while fewer cases were recorded in those relying on wells or ponds for their water supply, 1.7% and 1.2%, respectively. In contrast, cases were more severe and had a higher case fatality rate (8.6%) in villages supplied by wells compared with those relying on river or pond water, 2.5% and 0.8%, respectively. This discrepancy was presumed to reflect the inoculum size of infection made possible with water from wells when the latter were contaminated. In the three villages subjected to a special study, person-to-person transmission within family compounds did not seem to be an important factor since 74.5% of the cases in affected compounds occurred less than one month after the first case, and another 6.8% during the second month; thus, the majority were not Likely to be secondary cases.