PCP stands for Pneumocystis carinii pneumonia, which is an inflammation of the lungs caused by Pneumocystis carinii infection. Pneumocystis carinii is a protozoan parasite. It does not normally cause disease when a person comes into contact with it, but when a person’s resistance drops significantly, Pneumocystis carinii can invade the body and cause an infection. When it enters the lungs, it can cause pneumonia, which can lead to fever, cough, difficulty in breathing, diarrhea and other symptoms. Since healthy people are not susceptible to infection, Pneumocystis carinii pneumonia is an opportunistic infection that is most common in immunocompromised children and adults with immune deficiencies. The most common is AIDS, also known as Acquired Immunodeficiency Disease, and the most common cause of AIDS deaths.