Strongyloides is a small roundworm that infects the small intestine. Many cases are asymptomatic, but some infections produce diarrhea. In immunocompromised persons, especially those with AIDS, infection may spread to organs or tissues outside the intestine and become fatal. About 70%-80% of infected persons are said to have eosinophilia, but immunocompromised persons with systemic larval dissemination (“hyperinfection syndrome”) often have normal numbers of eosinophils. Diagnosis is usually made through stool examination, which contains rhabditiform larvae rather than ova. Single nonconcentrated stool examinations are said to be positive in only 30%-40% of cases, so that concentrating the specimen and (if negative) obtaining one or two more specimens on different days should be done if results of the first are negative. EIA for antibodies is available in some reference laboratories.