Current Epidemiology of Pneumocystis Pneumonia

Alison Morris; Jens D. Lundgren; Henry Masur; Peter D. Walzer; Debra L. Hanson; Toni Frederick; Laurence Huang; Charles B. Beard; Jonathan E. Kaplan


Emerging Infectious Diseases. 2004;10(10) 

In This Article


The first clinical cases of PCP were reported during World War II in orphanages in Europe. These cases of "plasma cell pneumonia" were common among malnourished children and were later reported in children in Iranian orphanages. The disease was then recognized in patients who were immunocompromised because of malignancies, immunosuppressive therapy, or congenital immunodeficiencies. Solid organ transplantation increased the number of patients at risk for PCP, although rates diminished after chemoprophylaxis was introduced. Without chemoprophylaxis, rates of PCP are 5%-25% in transplant patients, 2%-6% in patients with collagen vascular disease, and 1%-25% in patients with cancer. Defects in CD4+ lymphocytes are a primary risk factor for developing PCP, but the immune response to Pneumocystis is complex. CD8+ lymphocytes seem to be important in Pneumocystis clearance, and defects in B-cells and antibody production may also predispose to PCP.

The beginning of the AIDS epidemic in the early 1980s shifted the incidence of PCP from a rare disease to a more common pneumonia. Clusters of PCP cases in homosexual men and intravenous drug users were one of the first indications of the HIV epidemic.[2] PCP rapidly became the leading AIDS-defining diagnosis in HIV-infected patients. In the initial stages of the epidemic, PCP rates were as high as 20 per 100 person-years for those with CD4+ cell counts <200 cells/µL.[3] PCP was responsible for two thirds of AIDS-defining illnesses, and an estimated 75% of HIV-infected patients would develop PCP during their lifetime.[4]

The first substantial decline in the incidence of PCP occurred after the introduction of anti-Pneumocystis prophylaxis in 1989.[5] Although absolute numbers of cases of PCP as an AIDS-defining illness in the United States remained stable from 1989 to 1992 because of an increasing incidence of AIDS, the percentage of AIDS cases with PCP declined from 53% in 1989 to 49%, 46%, and 42% in 1990, 1991, and 1992, respectively (Centers for Disease Control and Prevention, AIDS Surveillance Summaries, 1989-1992). The later use of combination antiretroviral therapy further reduced the rates of PCP among adults by 3.4% per year after 1992.[1]


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.