Pneumocystis carini REF: Harrison's 17th ed chapter 182, CURRENT Medical Diagnosis & Treatment Chapter 31. HIV Infection & AIDS The host factors that predispose to the development of Pneumocystis pneumonia (PcP) include defects in cellular and humoral immunity. The risk of PcP among HIV-infected patients rises markedly when circulating CD4+ T cell counts fall below 200/[tL. Pneumocystis pneumonia is the most common oppounistic infection associated with AIDS. Pneumocystis pneumonia may be difficult to diagnose because the symptoms--fever, cough, and shoness of breath--are nonspecific. Other persons at risk for PcP are patients receiving immunosuppressive agents (paicularly glucocoicoids) for cancer and organ transplantation; those receiving biologic agents such as infliximab and etanercept for rheumatoid ahritis and inflammatory bowel disease; children with primary immunodeficiency diseases; and premature malnourished infants.