Pneumocystis pneumonia (PCP) or pneumocystosis is a form of pneumonia, caused by the yeast-like fungus found in the respiratory tracts of many mammals and humans.
Studies suggest that Pneumocystis organisms are communicable; airborne transmission has been reported. Pneumocystis organisms are commonly found in the lungs of healthy individuals. Most children are believed to have been exposed to the organism by age 3 or 4 years, and its occurrence is worldwide. It does not cause disease unless the immune system ceases to function properly.
PCP is the most common opportunistic infection and major cause of death in patients with AIDS in the United States. In persons without HIV infection, PCP also carries a severe prognosis; mortality rates of 30-50% have been documented in several large studies. The prognosis of PCP is worse in patients with the following: pulmonary disease, those who develop pneumothorax, and in patients who require mechanical ventilation. The higher mortality rate is likely a result of delayed diagnosis and delayed initiation of appropriate treatment.