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

UNLABELLED: 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.

IMPORTANCE: Haemophilus parainfluenzae is increasingly recognized as a potential pathogen in urogenital infections, particularly in sexually transmitted infection settings, yet its clinical relevance remains underappreciated. In this study, we show that multidrug-resistant strains are frequently associated with urogenital samples and can be isolated as the only detectable pathogen in symptomatic patients. Our findings highlight the important role of mobile genetic elements, including integrative and conjugative elements and small plasmids, in driving the spread of antimicrobial resistance across diverse bacterial lineages. We also identify capsular operons in a subset of isolates, supporting their potential role in niche adaptation and pathogenicity. Together, these results emphasize the need to consider H. parainfluenzae in the diagnosis and management of urogenital infections and underscore the importance of continued surveillance to monitor the emergence and dissemination of resistance.