title: Systematic review of outbreaks of Pneumocystis jirovecii pneumonia: evidence that P. jirovecii is a transmissible organism and the implications for healthcare infection control.
abstract: BACKGROUND
  Pneumocystis jirovecii pneumonia (PCP) is an important cause of morbidity and mortality in immunocompromised patients. Several nosocomial outbreaks of PCP have been reported in human-immunodeficiency-virus-negative, immunocompromised patients. The primary route of P. jirovecii transmission has yet to be proven; however, these outbreaks of infection suggest either interhuman transmission or a common environmental source.
  
  
  OBJECTIVE
  To identify and evaluate all published clusters and outbreaks of PCP. The main objective was to compare the epidemiology of the outbreaks, with a particular focus on the evidence for different modes of transmission.
  
  
  METHODS
  PubMed and EMBASE were searched to identify all English-language articles describing PCP outbreaks or clusters between 1980 and March 2015. Data were extracted on the outbreak setting, features of the outbreak, application of molecular typing, results of epidemiological assessment and environmental sampling.
  
  
  RESULTS
  Thirty outbreaks described in 29 articles were identified. Twenty-five (83%) of these outbreaks were described in patients who had undergone solid organ transplantation, primarily renal transplantation. All studies described a defined cohort of patients who shared some nosocomial facilities, including both inpatient and outpatient areas. Genotyping was undertaken in 16 (47%) studies. Cases with an identical genotype were demonstrated in all these studies.
  
  
  CONCLUSIONS
  The findings of this review raise a number of concerns regarding the public health and infection control implications of infection with PCP. The evidence presented for nosocomial acquisition and possible person-to-person transmission of infection suggests the need for formal infection control policies.
authors.affiliation: Nottingham University Hospitals NHS Trust, Nottingham, UK.
authors.forename: E P
authors.initials: EP
authors.lastname: Yiannakis
authors.affiliation: Nottingham University Hospitals NHS Trust, Nottingham, UK. Electronic address: tim.boswell@nuh.nhs.uk.
authors.forename: T C
authors.initials: TC
authors.lastname: Boswell
mesh_terms: D003428:Cross Infection / Q000453:epidemiology* / Q000635:transmission; D004196:Disease Outbreaks; D018562:Disease Transmission, Infectious; D006268:Health Facilities; D006801:Humans; D017053:Infection Control / Q000379:methods*; D045363:Pneumocystis carinii / Q000302:isolation & purification*; D011020:Pneumonia, Pneumocystis / Q000453:epidemiology* / Q000635:transmission
keywords: Clusters; Outbreaks; PCP; Pneumocystis jirovecii