There's a paper in the August 1 issue of Clinical Infectious Diseases of interest to the infection prevention community. In this French study, investigators sought to determine whether Pneumocystis jirovecii could be detected in the air near 19 patients who had documented infection with the organism. The proportion of samples yielding Pneumocystis significantly decreased with distance from the patient. Of samples obtained 1 m from the patient, 79% were positive; 69% were positive at a distance of 3 m from the patient; 42% at 5 m (at the entrance to the patient room); and 33% were positive at 8 m (in the corridor outside the patient room). The authors note that existing animal models have documented host-to-host transmission.
So the real question is whether current infection control guidelines are robust enough. CDC recommends not placing another immunocompromised patient in the same room as a patient with PJP (p. 108 of this document). Most HIV patients with PJP are initially placed in airborne precautions to rule out concomitant infection with M. tuberculosis. Tuberculosis can be ruled out in 1-2 days, and fortunately there were no positive samples at 5 or 8 m >1 day after the start of treatment for PCP.
My bigger concern is for transplant patients, who in many hospitals are geographically concentrated on specific units. Often these patients are able to ambulate in hallways, where they could encounter the organism outside an infected patient's room. Moreover, rooms in bone marrow transplant units are often at positive pressure, which would likely drive more organisms outside the room. I guess the good news is that we don't see many transplant patients with PJP since many receive prophylaxis for a period of time post-transplant, but it's probably an issue that we need to monitor a little more closely.