A method is described which led to the isolation of Shigella sonnei from well water suspected of being the primary foci in a school-associated shigellosis outbreak. In early November 1972, an epidemic of shigellosis occurred among 289 students and 25 staff members of a junior high school in Stockport, Iowa. The symptomatic disease involved 208 people. Rectal swabs were collected by the Iowa State Department of Health and an epidemiologist from the Center for Disease Control in Atlanta, Georgia. These specimens were sent to the State

The Directigen 1,2,3 Group A Strep Test (DGAST; BBL Microbiology Systems, Cockeysville, Md.) was compared with conventional culture methods for the detection of group A streptococci. Among 327 children, the DGAST had a sensitivity of 75.0%, a specificity of 99.1%, and positive and negative predictive values of 97.5 and 89.3%, respectively, as compared with 48-h culture results. The lower sensitivity (60.0%) in 322 adults was related to the low incidence of group A streptococcal pharyngitis in that population (7.8%). The positive and negative predictive values for adults were 93.8 and 96.7%, respectively. Only 3 of 327 (0.9%) pediatric and 2 of 322 (0.6%) adult specimens yielded uninterpretable results in the DGAST.

A method is described which led to the isolation of Shigella sonnei from well water suspected of being the primary foci in a school-associated shigellosis outbreak.