The fungus Pneumocystis jirovecii is responsible for pneumocystosis (PcP), a life threatening pneumonia in patients undergoing HSCT. The spontaneous attack rate of 16% within the first 6 months following allogeneic HSCT reported in the 1980's has considerably decreased with prophylaxis. However, PcP still remains a concern in the transplant ward with an incidence rate up to 2.5% in allo- and 1.4% in autologous HSCT but up to 7.2% on low dose of Dapsone. The mortality of PcP is especially high in HSCT recipients. One of the main factors of PcP after HSCT seems to be either the lack of TMP-SMX prophylaxis (all the other prophylactic drugs being inferior to TMP-SMX), or poor compliance to prophylaxis. Due to the rarity of the disease after HSCT, it is impossible to study it in monocenter studies, except on very long periods of time which may not reflect current practice. Several questions deserve investigations in a multicenter study, about timing, risk factors, and outcome.

Moreover, some European laboratories involved in the diagnosis of PcP have already given up to classical diagnostic methods and switched to qPCR. This implies that lower fungal burden can be detected and the clinical pertinence of such a diagnostic strategy deserves to be assessed.

Due to the lack of standardization, qPCR on sputum only will not be taken in account for the diagnosis of PcP. Knowing this is a non-interventional study, no additional visits or laboratory tests will be performed for the study. Only the available data will be collected.

Inclusion Criteria PCP cases:

• Allogeneic HSCT within the previous 24 months
• New case (first onset) of PcP documented in a BAL fluid, whatever the positive diagnostic test (cytology or IF or PCR) and whatever the presentation and treatment
• Any age
• Pre or post-transplant signed informed consent to enter the data in the EBMT registry

Exclusion Criteria PCP cases:

• Autologous HSCT
• Allogeneic HSCT recipient transplanted more than 24 months at time of the onset of PcP
• Second episode of PcP since allogeneic HSCT (patients who had experienced PcP before the allogeneic HSCT are not excluded).

All patients who have received an allogeneic HSCT during the last 24 months and who have a BAL fluid positive for Pneumocystis jirovecii (qPCR or IF or cytology) during the study period will be included, irrespectively of age, transplant characteristics and irrespectively to the fact that the patient has been treated for PcP or not.

Assuming an incidence of 3% after allogeneic HSCT, a total number of 3 300 allogeneic transplant (roughly 100 centers) would allow to expect 100 cases of PcP.