Molecular epidemiologic analysis of a Pneumocystis pneumonia outbreak among renal transplant patients

Area of Science:

• Medical Microbiology
• Infectious Diseases
• Transplant Medicine

Background:

• An outbreak of Pneumocystis pneumonia (PCP) occurred in renal transplant patients at Toho University Omori Medical Centre between November and December 2011.
• Pneumocystis jirovecii is an opportunistic pathogen causing PCP, particularly in immunocompromised individuals like transplant recipients.

Purpose of the Study:

• To investigate the genetic relatedness of Pneumocystis jirovecii strains involved in the 2011 outbreak.
• To determine if the outbreak was caused by a single or multiple strains of P. jirovecii using molecular epidemiology.

Main Methods:

• Multilocus sequence typing (MLST) was performed on DNA extracted from bronchoalveolar lavage fluid of five outbreak cases and 20 other PCP cases (2007-2014).
• Sanger sequencing was initially used, with ambiguous base calls addressed by next-generation sequencing (NGS) for precise strain typing.
• Analysis focused on identifying genetic similarities and variations in P. jirovecii strains.

Main Results:

• Four of the five patients in the 2011 outbreak and two additional renal transplant patients from 2013 showed highly homologous P. jirovecii DNA sequences.
• NGS analysis of overlapping bases indicated near-identical ratios of differing bases, suggesting a single predominant strain.
• The findings strongly indicate that the PCP outbreak was caused by a common P. jirovecii strain.

Conclusions:

• The PCP outbreak at Toho University Omori Medical Centre was likely caused by a single strain of Pneumocystis jirovecii.
• The observed genetic variations may be attributed to the diploid nature of P. jirovecii.
• Molecular epidemiology is crucial for tracking infectious disease outbreaks in vulnerable patient populations.