less than 200/μL. In populations who do not have access to preventive treatment, PCP continues to be a major cause of death in AIDS. History The first cases of Pneumocystis pneumonia were described in premature infants in Europe following the Second World War. It was then known as plasma cellular interstitial pneumonitis of the newborn. In the era before the existence of HIV/AIDS in humans, clinical transplant immunology, and widespread immunomodulatory therapy for autoimmune diseases, the neonatal and infantile population was the principal immunity-limited population. For example, a 1955 review article stated, "Interstitial plasma cell pneumonia is a type of infantile pneumonia, occurring chiefly in Europe." It also stated, "The etiology is unknown, but the disease acts like an infection in its epidemiology. No present-day therapeutic measures seem to be of any definite value." Nomenclature Both Pneumocystis pneumonia and pneumocystis pneumonia are orthographically correct; one uses the genus name per se and the other uses the common noun based on it. (This is the same reason, for example, why "group A Streptococcus" and "group A streptococcus" are both valid.) Synonyms for PCP include pneumocystosis (pneumocystis + -osis), pneumocystiasis (pneumocystis + -iasis), and interstitial plasma cell pneumonia. The older species name Pneumocystis carinii (which now applies only to the Pneumocystis species that is found in rats) is still in common usage. As a result, Pneumocystis pneumonia (PCP) is also known as Pneumocystis jiroveci[i] pneumonia and (incorrectly) as Pneumocystis carinii pneumonia. Regarding nomenclature, when the name of Pneumocystis pneumonia (PCP) changed from P. carinii pneumonia to P. jirovecii pneumonia, it was at first asked whether "PJP" should replace "PCP". However, because the short name "PCP" was already well established among physicians that managed patients with Pneumocystis infection, it was widely accepted that this name could continue to be used, as it could now stand for pneumocystis p''neumonia. References External links Animal fungal diseases Pneumonia HIV/AIDS Atypical pneumonias Fungal diseases