Molecular Demonstration of a Pneumocystis Outbreak in Stem Cell Transplant Patients: Evidence for Transmission in the Daycare Center

Abstract

Pneumocystis jirovecii pneumonia (PCP) is a life-threatening infection in hematology. Although occasionally reported, the role of interhuman transmission of P. jirovecii in PCP, compared to that of reactivation, remains an unresolved question; the recommendation to isolate PCP patients in the hematology ward are not well evidence-based. Following an unexpected increase in the number of febrile pneumonia patients with P. jirovecii DNA detected in respiratory samples in our hematology ward, we explored 12 consecutive patients from November 2015 to May 2016. Genotyping of P jirovecii was performed using microsatellite markers. The frequency of simultaneous occupancy of these 12 patients in the same unit on the same day from 4 months prior to the first diagnosis was recorded. In three patients, the P. jirovecii genotype could not be determined because DNA was insufficient. One rare single genotype (Gt2) was found in four of the other nine, all allogeneic stem cell transplant recipients. The transmission map showed that these 4 patients had multiple opportunities to meet on the same day (median, 6.5; range, 4-10) at the daycare center. It was much less among the eight non-Gt2 patients (median, 1; range, 0-9; P = 0.048). This study, based on modern molecular technics, strongly suggests that interhuman transmission of P. jirovecii between allogeneic stem cell transplant recipients is possible. P. jirovecii DNA detected in respiratory specimens supports that isolation and respiratory precautions be recommended in such cases in the hematology ward.

Keywords: Pneumocystis jirovecii; genotyping; microsatellite; nosocomial infection; short tandem repeat.

Figure 1

Number of pneumocystis cases observed in the hematology department between January 2013 and May 2016.

Figure 2

Transmission map of the 4 patients infected with genotype 2 Pneumocystis jirovecii in the hematology ward, showing that any meeting between two Gt2 patients must have been in the daycare center because no 2 patients were concomitantly hospitalized in the same unit of the ward. Patient 2 met Patients 5 and 10 once each before developing PCP and twice each after developing PCP while under treatment followed by secondary prophylaxis, including once when both were met on the same day. Patient 2 never met Patient 7. Patient 5, the only one to have met all 3 others at least once, met Patient 2 three times, Patient 7 twice, and Patient 10 five times. Patient 7 met Patient 5 twice and Patient 10 three times (twice before the diagnosis of PCP, and once thereafter). Patient 7 never met Patient 2. Patient 10 met Patient 2 twice and Patient 5 five times, including one occurrence where both were met on the same day. Patient 10 met Patient 7 three times.