Using epidemiologic tools to control an outbreak of diarrhoea in a textile factory, Bulawayo, Zimbabwe

Dysentery is endemic in Zimbabwe. More than 260,000 cases and a case fatality of four per thousand were reported in 1993. In late July 1994, the Health Services Department in Bulawayo was informed of two cases of Shigella dysenteriae type I at a textile factory that employs 138 workers. Workers were interviewed at the factory regarding the date of the onset of illness, symptoms, food consumed, and treatment received. Factory water supply, cooking, and sanitary facilities were inspected. Stool and water samples were obtained for analysis. A case was defined as an employee presenting with diarrhoea with onset from July 24 to August 25, 1994. Of the 99 workers on day and evening shifts, 75 (75%) were interviewed. Thirty eight workers met the case definition (Attack Rate 51%). Common symptoms were abdominal cramps (71%), and blood in stools (37%); median duration of diarrhoea was 11 days (range 5 to 32 days). Thirty seven (64%) of 58 workers who drank borehole water were ill compared to one (6%) of the 17 who did not (RR = 10.8, 95% CI = 1.6-73). No food items consumed were significantly associated with the illness. Two different shigella species (2 sonnei and 2 boydii) were isolated from five (13%) of 38 stool specimens. Water samples from the two boreholes yielded numerous faecal coliforms. Neither borehole was registered as required by the municipal bylaws, which also forbid use of borehole water for drinking. The epidemiologic and laboratory evidence implicate contaminated borehole water as the most likely cause of this outbreak. Enforcement of municipal bylaws on drilling, registration and use of boreholes is essential to avoid further outbreaks of waterborne diseases.