Pneumocystis jiroveci, previously known as Pneumocystis carnii, is a fungus that can cause pneumonia in immunosuppressed humans. It was initially discovered in malnourished children, but has since been found in HIV patients and patients who have received solid organ transplants and are on immunosuppressive medications.
Patients with PCP will have shortness of breath, fever, and a nonproductive cough. Chest xray will show bilateral diffuse infiltrates. Diagnosis is made when you isolate the organism, but an LDH level gives some idea of the level of lung involvement. The higher the LDH level in PCP, the worse the lung injury. You can trend out the LDH level as you treat the disease and it should decrease as the patient gets better.
Treat PCP with 21 days of either Bactrim or Pentamidine in HIV patients, and with 14 days of the same antibiotics in other immunocompromised patients.