The role of person-to-person transmission in an epidemiologic study of Pneumocystis carinii pneumonia.

OBJECTIVE

Recent laboratory studies suggest that may be transmitted from person-to-person. Recent exposure to persons with pneumonia (PCP) among HIV-infected persons with and without PCP was assessed to evaluate the person-to-person transmission hypothesis.

DESIGN

A case-control study design was used.

METHODS

In Seattle and Los Angeles, a history of contact with persons with PCP was compared between HIV-infected patients with laboratory-confirmed PCP (n = 209) and HIV-infected patients with no history of PCP (n = 254).

RESULTS

No association was found between past exposures to persons with PCP and an increased odds for PCP [odds ratio (OR), 0.6; 95% confidence interval (CI), 0.3-1.1] in the total study group. In addition, no association was observed when the analysis was restricted to cases and controls who were not on adequate PCP prophylaxis in the previous 3 months (OR, 0.7; 95% CI, 0.3-1.5). Most cases in Los Angeles (95%) and Seattle (96%) were not receiving PCP prophylaxis in the 3 months prior to a PCP diagnosis. Many controls in Los Angeles (54%) and Seattle (47%) were also not on prophylaxis. In addition, 23% of the Seattle cases and 42% of the Los Angeles cases were unaware of their HIV infection at the time of their PCP diagnosis.

CONCLUSIONS

Although most participants were not on adequate prophylaxis, we found no evidence of person-to-person transmission of Pneumocystis carinii in a population with advanced HIV disease. The difficulty quantifying past exposures to persons with PCP is a limitation of this type of research.