Epidemiology and antimicrobial resistance trends in Haemophilus parainfluenzae in a tertiary care hospital (2018–2022)

Abstract

Haemophilus parainfluenzae is increasingly recognized as a reservoir of antimicrobial resistance in urogenital infections. We conducted a retrospective laboratory-based study including all H. parainfluenzae isolates collected at a tertiary hospital in Barcelona between 2018 and 2022. Antimicrobial susceptibility testing was performed for all isolates, and whole-genome sequencing was conducted for multidrug-resistant (MDR) and capsulated strains. A total of 529 isolates from 504 individuals were analyzed (258 respiratory, 223 urogenital, and 48 other sources). Overall, 85/529 (16.1%) isolates were MDR, with a significantly higher prevalence among urogenital compared with respiratory samples (30.5% vs 6.2%). Among symptomatic urogenital episodes caused by MDR isolates, H. parainfluenzae was the only sexually transmitted infection (STI)-associated urogenital pathogen organism recovered in 65.3% of cases. Resistance was mediated by acquired genes and target-site substitutions, including β-lactamases (blaTEM-1, blaROB-1, and blaCTX-M-15), PBP3 substitutions, macrolide efflux determinants, quinolone resistance-determining regions mutations, and determinants conferring resistance to chloramphenicol, folate pathway inhibitors, and tetracyclines. Mobile genetic elements were frequent, including diverse integrative and conjugative elements, chromosomal insertions, and small β-lactamase plasmids distributed across genetically diverse lineages, with no evidence of a dominant MDR clone. Capsular operons were detected in 6.6% of the isolates, mainly urogenital, including two operons not observed previously at our center; 26/35 capsulated isolates were MDR, and capsular loci occurred across multiple lineages. These findings support H. parainfluenzae as an STI-associated urogenital pathogen and highlight the widespread distribution of mobile resistance determinants, reinforcing the need for continued genomic surveillance.