The epidemiologist in Dammam, Saudi Arabia, noticed a steady increase in salmonellosis reports from 1992 to 1994. The epidemiologic pattern of these cases was unusual in three respects: 80% were single cases in families without known contact with another case, there was no apparent time and space relationship between cases, and 85% were among children under 6 years of age. We suspected a widely distributed food or water source with a low dose of Salmonella and began an investigation to identify this possible source.
Methodology
For six weeks we intensified ongoing surveillance from all medical facilities serving Dammam and identified all patients seeking treatment for gastroenteritis and fever from whom Salmonella were isolated (cases). For each case, we selected two age-matched controls visiting the same medical facility for other reasons during the same week as the case. We interviewed parents of case- and control-children about household potable water sources, milk and formula, and consumption of undercooked eggs and other foods. We reviewed potable water distribution for Dammam.
Results
We identified 52 cases (median age 14 months) and 104 controls. Illness was associated with drinking well water trucked to the house (odds ratio [OR] = 12.6, 95% confidence interval [CI] 5.3-31) and 80% of cases used trucked water. Obtaining potable water from government reservoirs was protective (OR = 0.2, 95% CI 0.05-0.56), while water from two other sources was not related to salmonellosis. Thirty percent of case-children under 2 years old ate undercooked eggs (OR = 5.0, 95% CI 1.4-20). In the same age group, breast-feeding (OR = 0.81, 95% CI 0.24-2.63) and bottle-feeding (OR = 1.6, 95% CI 0.6-4.2) were not related to salmonellosis. Chlorination of water in government and private reservoir tanks had been routinely checked; however, no testing of residual chlorine had been done on trucked water from the four private companies.
Conclusion
Potable water from private companies trucked to households is a major source for ongoing salmonellosis in Dammam, while undercooked eggs have a limited contribution. In the Middle East, scarcity of potable water is related to an increase in potable water providers. This will continue to increase the burden on governments for close monitoring and supervision to prevent waterborne disease.