Pneumocystis pneumonia, or PCP, is a life-threatening lung disease caused by an organism called Pneumocystis jiroveci (until a few years ago, the organism Pneumocystis carinii was believed to be the causes of PCP in humans). This organism can also infect and cause disease in other organs, including the skin (extrapulmonary Pneumocystis infection).
Pneumocystis jiroveci (yee-row-vet-zee) is abundant in the environment. Most healthy people have antibodies to fight this organism every time it enters the body. However, in people with compromised immune systems—such as people with AIDS and those receiving chemotherapy for cancer—antibody responses to Pneumocystis jiroveci fade, rendering them susceptible to PCP.
During the early years of the AIDS epidemic, PCP occurred in more than 80% of people living with HIV. It was also highly fatal. However, drugs to prevent PCP have drastically decreased these rates and these drugs are now recommended for all HIV-infected people who see their CD4 cell count drop below 200.
PCP is preventable.