An outbreak of toxoplasmosis on an Illinois farm.

Two siblings residing on a farm in Illinois were concurrently hospitalized with cervical lymphadenitis. Clinical and serologic evidence indicated that the etiology of the lymphadenitis in each case was toxoplasmosis. The simultaneous occurrence of two cases of toxoplasmosis in a household prompted a prospective investigation of 11 other immediate family members for evidence of disease. During the next month seven of the other family members developed serologic evidence of acute toxoplasmosis. Four of these seven individuals were symptomatic. Investigation of the family's home environment failed to unequivocally identify a common source of infection, but epidemiologic evidence suggested that this outbreak was related to contact with sick cats.