Geographic distribution of human immunodeficiency virus-associated Pneumocystis carinii pneumonia in San Francisco.

The epidemiology of Pneumocystis carinii pneumonia (PCP) and its geographic distribution are incompletely understood. We examined the influence of geographic location as a risk factor for PCP through a retrospective case-control study of HIV-infected persons evaluated for PCP at San Francisco General Hospital. Subjects had microscopically confirmed PCP diagnosed between January 1996 and June 1999. Control subjects had a presentation suggestive of PCP, but had bronchoalveolar lavage examination that did not reveal P. carinii. Medical chart review was performed to obtain demographic and clinical characteristics of the subjects as well as their addresses at time of PCP evaluation. Multivariate analyses were performed in order to identify variables associated with PCP. Lack of P. carinii prophylaxis and a CD4 cell count </= 50 cells/microl were independent predictors of an increased risk of PCP. Interestingly, subjects living in the 94103 zip code had a significantly lower risk of PCP than subjects in other areas (odds ratio = 0.2, 95% confidence interval 0.1-0.6, p < 0.01). This effect was present despite controlling for risk factors for PCP such as use of prophylaxis or antiretroviral therapy, CD4 cell count, and HIV RNA level. We conclude that residence in the 94103 zip code of San Francisco is associated with a substantially lower risk of PCP than residence in other areas of the city.