Pneumocystosis is a fungal infection that most often presents as Pneumocystis pneumonia in people with HIV/AIDS or poor immunity. It usually causes cough, difficulty breathing and fever, and can lead to respiratory failure. Involvement outside the lungs is rare but, can occur as a disseminated type affecting lymph nodes, spleen, liver, bone marrow, eyes, kidneys, thyroid, gastrointestinal tract or other organs. If occurring in the skin, it usually presents as nodular growths in the ear canals or underarms.
It is caused by Pneumocystis jirovecii, a fungus which is usually breathed in and found in the lungs of healthy people without causing disease, until the person's immune system becomes weakened.
Diagnosis is by identifying the organism from a sample of fluid from affected lungs or a biopsy. Prevention in high risk people, and treatment in those affected is usually with trimethoprim/sulfamethoxazole (co-trimoxazole).
The prevalence is unknown. Less than 3% of cases do not involve the lungs. The first cases of pneumocystosis affecting lungs were described in premature infants in Europe following the Second World War.