An outbreak of leptospirosis in Washington State

The results of an investigation of an outbreak of 61 cases of leptospirosis, which occurred among teenaged children in southeastern Washington between June 20 and August 20, 1964, are described. The illnesses, in most instances, were characterized by a benign course of headache, chills, fever, myalgia, and nausea. About half the cases had a stiff neck. The outbreak was associated with the use by the involved teenagers of an irrigation canal as a "swimming hole." Approximately 200 yards upstream from the "swimming hole" a herd of cattle was pastured. This herd had direct access to the irrigation canal at this point. Nine (21%) of 43 cattle cultured were shedding leptospires in early September 1964. Organisms were also cultured from samples of water standing on the pasture in early September. Cross-agglutination and agglutination-absorption studies on the isolates from the cattle and the water revealed them to he a new serotype in the Pomona group, which has been named kennewicki. Serologic data obtained using the microscopic agglutination test, a macroscopic slide test, and the genus specific hemolytic test, are presented.