Comparison of methods for identification of Pneumocystis carinii in pulmonary aspirates

Specimens obtained by percutaneous pulmonary needle aspiration from patients suspected of having P. carinii pneumonitis were examined by five staining methods. With polychrome methylene blue (Hema Tek), Wright, and Giemsa stains, P. carinii could unequivocally be identified in three developmental stages: 'cyst,' 'sporozoite,' and 'trophozoite.' Although the contrast of organism against host tissue cells was not outstanding, the simplicity, consistency, and rapidity of the methods were the major advantages. Toluidine blue O stain and methenamine silver nitrate stains provided easy recognition of the organisms, with marked contrast between the organisms and host cells. However, the intracystic structures and trophozoites could not be identified with these stains. It is suggested that the clinical specimen be stained first with the more rapid and simple stains, and if the organism is not found, the methenamine silver stain should be used to arrive at a final conclusion.