Pneumocytosis refers to a medical condition that affects the lungs. This condition is also known as pneumocystis pneumonia or PCP. There are several synonyms used to describe this condition, including pneumocystosis or P. jiroveci pneumonia. It is an opportunistic infection that mainly affects people with weakened immune systems, especially those living with HIV. The symptoms of pneumocytosis usually include coughing, difficulty in breathing, chest pain, and fever. Treatment of pneumocytosis requires the use of antibiotics to kill the microorganisms that cause the infection. The earlier the diagnosis of pneumocytosis, the higher the chances of successful treatment.