Shigellosis from swimming

In Augsut 1974, 31 of 45 cases of Shigella sonnei infection in Dubuque, Iowa, were traced to swimming in an 8-km stretch of the Mississippi River. Comparison of the first case in each affected family with neighborhood controls showed a significant correlation between swimming and illness (P less than .0001). A significant association between diarrheal illness and swimming (P less than .0001) was also demonstrated by a retrospective survey of 60 families who had camped at a park beside the river; the attack rate for swimmers who got water in their mouths while swimming was 18%. They had been swimming in water where the mean fecal coliform count was 17,500 organisms per 100 ml; the federal recommended upper limit for swimming water is 200 per 100 ml. A water sample obtained at the park swimming area one month after authorities had banned swimming in the area yielded S sonnei with the same antibiogram, colicin type, and phage type as the isolates from six swimmers.¿