Environmental mycological studies on the causative agent of summer-type hypersensitivity pneumonitis.

Environmental mycological studies were carried out in 22 homes of patients with summer-type hypersensitivity pneumonitis and in 195 homes of control subjects. In 10 patients' homes, indoor sampling was performed by open-plate culture, house dust culture, and swab culture (group 1), but in the other 12 patients' homes, sampling was only by house dust culture (group 2). We isolated 302 strains of yeasts from the 22 patients' homes and 962 strains of yeasts from the homes of control subjects. The incidence of yeasts, except genera Trichosporon, was not significantly different between homes of patients and control subjects when homes were assessed by three culture methods. T. cutaneum was isolated from seven of 10 patients' homes in group 1, and their colonizing places were revealed by the swab culture method. In group 2, the cells were isolated from four of 12 patients' homes. No T. cutaneum, however, was isolated from the control subjects' homes. Among the isolated yeasts from patients' homes, 23 strains were reactive to the patients' sera at 1:128 or higher in indirect fluorescent antibody titers; 10 yeasts were T. cutaneum, isolated from 10 homes of 14 patients, but the other 13 yeasts were each a different species isolated from 10 different homes. Furthermore, inhalation challenge with the culture-filtrate antigen prepared from T. cutaneum was performed on the nine patients of six homes in group 1 and the two asymptomatic family members. Of the nine patients, six were positive, one was probable, and two patients were negative. Neither of the two asymptomatic family members responded. These results suggest that T. cutaneum is a major causative agent of summer-type hypersensitivity pneumonitis.