Evaluation of an intervention program for the control of an outbreak of shigellosis among institutionalized persons

After control measures were initiated to stop an outbreak of shigellosis in an institution for the developmentally disabled, there was a sharp decline in the number of cases of Shigella sonnei infection. Among ill residents, those treated with antibiotics had shorter mean duration of diarrhea (2.4 vs. 4.5 days, P < .01) and were less likely to have stool cultures positive for shigellae 2-4 weeks after onset of diarrhea (0/25 vs. 5/19; relative risk [RR] = undefined; P = .02). The attack rate was higher in villages where segregation of ill residents was not practiced (46/73 vs. 53/155; RR = 1.8; 95% confidence limits [CL], 1.4, 2.4). In individual housing units where ill residents were not segregated (preintervention), a correlation was found between mean duration of diarrhea and unit attack rates (r = .88; 95% CL, 0.29, 0.99). A study of all 305 residents 10 weeks after the intervention began revealed no positive stool cultures.