Pneumocystis pneumonia (PCP) is a type of lung infection caused by the fungus Pneumocystis jirovecii. It primarily affects individuals with weakened immune systems, such as those with HIV/AIDS, cancer, or those taking immunosuppressive medications. Symptoms often include a persistent cough, fever, and difficulty breathing. Diagnosis typically involves imaging tests like chest X-rays and laboratory tests to identify the fungus. Treatment usually includes antibiotics, such as trimethoprim-sulfamethoxazole, which are effective in combating the infection. Early detection and treatment are crucial for improving outcomes in affected individuals.