Outbreaks and clustering of Pneumocystis pneumonia in kidney transplant recipients: a systematic review

From 1980 onwards, an increasing number of outbreaks of Pneumocystis pneumonia (PCP) among kidney transplant recipients have been reported. The cause of these outbreaks is unclear and different explanations have been provided. We performed a systematic review to provide a comprehensive overview of the epidemiologic characteristics as well as the involved clinical risk factors. A total of 15 peer-reviewed English language articles published from 1980 onward were included. Outbreak settings were all marked by absence of adequate chemoprophylaxis, frequent inter-patient contacts and lack of isolation measures taken during hospitalization of PCP cases. PCP-associated mortality rates significantly decreased from a weighted mean of 38% before 1990 to 19% and 13% in the following two decades. Clinical risk factors for PCP in outbreak settings were largely similar to non-outbreak settings. Genotyping by multilocus sequence typing (MLST) or comparison of the internal transcribed spacer (ITS) regions 1 and 2 showed that the outbreaks are most frequently caused by a predominant or a single Pneumocystis strain. Pooled epidemiological data and genotyping results strongly support the theory that interhuman transmission of Pneumocystis occurred. No seasonal trend was noted. The results emphasize the need for chemoprophylaxis in kidney transplant recipients despite a low baseline incidence of PCP in this population, and support the current CDC recommendation with regard to isolation of patients with PCP during hospitalization.