Survival and infectivity of Pneumocystis carinii outside the mammalian host.

Air blower prefilters servicing HEPA-filtered Biobubble housing Pneumocystis carinii-infected rats were stored for up to five months at -80 degrees C to room temperature. After storage, 76% of immunosuppressed rats exposed to these prefilters developed P. carinii infections. In contrast, only 4% of control immunosuppressed rats exposed to autoclaved filters had P. carinii infections. These observations indicate that the organism has a dormant form that remains infective for at least several months outside the mammalian host.