During the last six years sporadic Vibrio cholera infections have reappeared each summer in the neighboring cities of Dammam, Khobar, and Qatif, Eastern province, Saudi Arabia. In 1995 we conducted an epidemiological investigation to identify the mode of transmission and the source of the V cholera O-1.
Methodology
A locally acquired V. cholerae O-1 infection was defined as isolation of V. cholerae O-1 from a symptomatic person who did not arrive in the Eastern province three days before diarrhea onset or the eight weeks before culture (for asymptomatic persons). We reviewed the surveillance reports of all V.cholera O-1 infections. For each locally acquired V cholerae O-1 infection, five control-persons were selected, matched for district clinic, sex, nationality, occupation, and age. We interviewed the infected persons and controls inquiring on travel, exposure to diarrhea patients, and food and water consumed.
Results
From May 21, 1995 through September 24, 1995, surveillance detected 11 persons with locally acquired V.cholera O-1 infection. Eight had diarrhea with onset throughout the summer, and three were asymptomatic. These persons lived in 10 widely scattered residences throughout the three cities. Eight were available for interview. V. cholera O-1 infection was more likely (matched odds ratio [MOR] = undefined p < 0.05) to occur in persons who drank water obtained in jerry cans from one private water company (company A). This association was stronger if the hired family driver brought the water (MOR = undefined, p <0.01). Residual chlorine was more often undetectable in jerry can water from case families than control families. Water from company A was desalinized well water (by electrodialysis) trucked to a distribution tank in central Dammam where customers filled their jerry cans.
Conclusion
Bulk water from company A sold by jerry can was the most probable mode of transmission of locally acquired V. cholera O-1 infection in the Eastern province in the summer of 1995. Since the water was manipulated at several points in the chain of delivery from the water production plant to the house, the source of contamination could not be determined. The government provides free chlorinated drinking water and the public needs to be advised that they should use this safe source.