Genotype distribution of Pneumocystis jirovecii in immunocompromised patients: a single-center molecular epidemiology study

Background Pneumocystis jirovecii pneumonia (PCP) remains a major opportunistic infection affecting both HIV-infected and non-HIV immunocompromised individuals. Key aspects of its transmission dynamics in complex healthcare environments remain poorly understood. Methods We conducted a descriptive molecular epidemiology study to characterize the genetic diversity of P. jirovecii in a large tertiary-care hospital in São Paulo, Brazil. Respiratory samples collected from hospitalized and outpatient individuals undergoing molecular investigation for PCP between 2014 and 2015 were analyzed. PCR-positive specimens were genotyped by sequencing the mitochondrial large subunit rRNA (mtLSUrRNA) locus. Results Among 80 patients tested, 58 samples were successfully sequenced, including individuals living with HIV/AIDS (39.7%), solid organ transplant recipients (32.8%), and patients with other immunosuppressive conditions (27.6%). Three genotypes were identified. Genotype 3 predominated across all clinical groups (69%), whereas genotypes 2 and 1 accounted for 12% and 7%, respectively. Mixed infections were detected in 12% of cases. Conclusions In this descriptive molecular epidemiology study, genotype 3 predominated across diverse immunocompromised populations within a large tertiary-care hospital. These findings should be interpreted as hypothesis-generating and may reflect underlying genotype distribution or shared environmental exposure. Further studies incorporating higher-resolution typing methods and clinical correlation are needed to better define transmission pathways.