Pneumocystis carinii pneumonia is one of the most common and well-known opportunistic infections that can occur in patients with AIDS due to reduced immune function after they enter the AIDS stage. Pneumocystis is a fungus that causes chronic cough, fever, respiratory distress, and decreased partial pressure of oxygen in patients with AIDS. In addition to Pneumocystis pneumonia, patients can also develop cryptococcal meningitis, Candida albicans esophagitis, herpes zoster, and giant cell retinitis.