Hemolytic-uremic syndrome and Escherichia coli O121 at a Lake in Connecticut, 1999

Objective. Non-O157 Shiga toxin-producing Escherichia coli (STEC) have emer ged as an important public health problem. Outbreaks attributed to non-O157 STEC rarely are reported. In 1999, follow-up of routine surveillance repor ts of children with hemolytic-uremic syndrome (HUS) identified a small clus ter of 3 cases of HUS, all of whom had spent overlapping time in a Connecti cut lake community in the week before onset of symptoms. We conducted an in vestigation to determine the magnitude and source of the outbreak and to de termine risk factors associated with the transmission of illness. Methods. We conducted a cohort study and an environmental investigation. Th e study population included all people who were at the lake in a defined ge ographic area during July 16-25, 1999. This time and area were chosen on th e basis of interviews with the 3 HUS case-patients. A case was defined as d iarrhea ( 3 loose stools/d for greater than or equal to3 days) in a person who was at the lake during July 16-25, 1999. Stool samples were requested f rom any lake resident with diarrheal illness. Stools were cultured for Salm onella, Shigella, Campylobacter, and E coli O157. Broth cultures of stools were tested for Shiga toxin. Case-patients were asked to submit a serum spe cimen for antibody testing to lipopolysaccharides of selected STEC. Environ mental samples from sediment, drinking water, lake water, and ice were obta ined and cultured for E coli and tested for Shiga toxin. An environmental e valuation of the lake was conducted to identify any septic, water supply sy stem, or other environmental condition that could be related to the outbrea k. Results. Information was obtained for 436 people from 165 (78%) households. Eleven (2.5%) people had illnesses that met the case definition, including the 3 children with HUS. The attack rate was highest among those who were younger than 10 years and who swam in the lake on July 17 or 18 (12%; relat ive risk [RR]: 7.3). Illness was associated with swimming (RR = 8.3) and wi th swallowing water while swimming (RR = 7.0) on these days. No person who swam only after July 18 developed illness. Clinical characteristics of case -patients included fever (27%), bloody diarrhea (27%), and severe abdominal cramping (73%). Only the 3 children with HUS required hospitalization. No bacterial pathogen was isolated from the stool of any case-patient. Among l ake residents outside the study area, E coli O121: H19 was obtained from a Shiga toxin-producing isolate from a toddler who swam in the lake. Serum wa s obtained from 7 of 11 case-patients. Six of 7 case-patients had E coli O1 21 antibody titers that ranged from 1:320 to >1:20 480. E coli indicative o f fecal contamination was identified from sediment and water samples taken from a storm drain that emptied into the beach area and from a stream bed l ocated between 2 houses, but no Shiga toxin-producing strain was identified . Conclusions. Our findings are consistent with a transient local beach conta mination in mid-July, probably with E coli O121: H19, which seems to be abl e to cause severe illness. Without HUS surveillance, this outbreak may have gone undetected by public health officials. This outbreak might have been detected sooner if Shiga toxin screening had been conducted routinely in HU S cases. Laboratory testing that relies solely on the inability of an isola te to ferment sorbitol will miss non-O157 STEC, such as E coli O121. Serolo gic testing can be used as an adjunct in the diagnosis of STEC infections. Lake-specific recommendations included education, frequent water sampling, and alternative means for toddlers to use lake facilities.