Outbreak of Pneumocystis jiroveci pneumonia in renal transplant recipients: P. jiroveci is contagious to the susceptible host.

Background: Prophylaxis against Pneumocystis jiroveci pneumonia (PCP) is only recommended during some periods after renal transplantation. Recent advances in immunosuppressive therapy have considerably reduced acute rejection. However, the reported PCP outbreaks are increasing in renal transplant recipients.
Methods: Only three sporadic PCP cases had occurred since 1976 in our Renal Transplant Unit until the index case in July 2004. A PCP outbreak of 27 cases occurred mainly in the outpatient clinic within 1 year, followed by six additional cases during the next 3 years. Molecular analysis of P. jiroveci and surveys of reservoir were performed.
Results: Molecular analysis documented that all cases were caused by the same strain. Among 27 cases of the outbreak, human-to-human transmissions were traceable in 22 cases based on dates of outpatient clinic visits and in four cases during hospitalization. Based on the confirmed cases, airborne transmission was suspected with an estimated median PCP incubation period of 53 days (range 7-188 days). Surveys for reservoir of P. jiroveci identified asymptomatic carriers and environmental contamination. Some sporadic cases might be caused by reservoirs. Among the 33 cases, none had received PCP prophylaxis, 22 cases had PCP over 12 months, and six cases over 10 years after renal transplantation.
Conclusion: On documentation of a PCP case, we recommend PCP prophylaxis for a maximum period of 6 months (upper limit of incubation period) in all renal transplant recipients including those on regular maintenance immunosuppressive therapy.