Genetic and Epidemiologic Analyses of an Outbreak of Pneumocystis jirovecii Pneumonia Among Kidney Transplant Recipients in the United States

Background Pneumocystis jirovecii is an opportunistic fungus that causes Pneumocystis pneumonia (PCP) in immunocompromised hosts. Over an 11-month period, we observed a rise in cases of PCP among kidney-transplant recipients (KTR), prompting an outbreak investigation. Methods Clinical and epidemiologic data were collected for KTR diagnosed with PCP between July 2019 and May 2020. Pneumocystis strain typing was performed using restriction fragment length polymorphism analyses and multilocus sequence typing in combination with next-generation sequencing. A transmission map was drawn, and a case-control analysis was performed to determine risk factors associated with PCP. Results Nineteen cases of PCP in KTR were diagnosed at a median of 79 months post-transplantation; 8 received monthly belatacept infusions. Baseline characteristics were similar for KTR on belatacept versus other regimens; the number of clinic visits was numerically higher for the belatacept group during the study period (median 7.5 vs 3). Molecular typing of respiratory specimens from 9 patients revealed coinfection with up to 7 P. jirovecii strains per patient. A transmission map suggested multiple clusters of interhuman transmission. In a case-control univariate analysis, belatacept, lower absolute lymphocyte count, non-White race, and more transplant clinic visits were associated with an increased risk of PCP. In multivariate and prediction power estimate analyses, frequent clinic visits was the strongest risk factor for PCP. Conclusions Increased clinic exposure appeared to facilitate multiple clusters of nosocomial PCP transmission among KTR. Belatacept was a risk factor for PCP, possibly by increasing clinic exposure through the need for frequent visits for monthly infusions. In a Pneumocystis jiroveci pneumonia (PCP) outbreak among 19 kidney-transplant recipients in the United States, strain genotyping suggested coinfection and interhuman transmission of multiple P. jiroveci strains. Belatacept was a risk factor for PCP, potentially via increased clinic exposure.