Rising antimicrobial resistance and epidemiology of Haemophilus spp. in urethritis: A 4-year analysis

The role of Haemophilus spp. in nongonococcal urethritis remains undercharacterized. We aimed to assess its prevalence, resistance patterns, and behavioral associations.

Urethral samples from symptomatic men ≥18 years at two sexually transmitted infection clinics (STI) in Lyon, France (2021-2024), underwent PCR for Chlamydia trachomatis, Neisseria gonorrhoeae, and Mycoplasma genitalium, and culture for Haemophilus spp. Positive Haemophilus samples were included; species were identified, antimicrobial susceptibility tested when possible, and behavioral data collected.

Among 2021 samples, Haemophilus spp. was detected in 339 (16.8%), as sole pathogen in 196 (9.7%). Haemophilus parainfluenzae predominated (77.8%) over Haemophilus influenzae (22.2%; P < 0.001). Co-detection with other pathogens was associated with men-having-sex-with-men (odds ratios [OR] = 1.76, 95% confidence intervals [CI] [1.09-2.90]), drug use (OR = 2.33, 95% CI [1.40-3.93]) and recent STI (42.7% vs 29.6%; P = 0.018; OR = 1.77; 95% CI [1.12-2.78]). No temporal increase was observed. Among 49 isolates, H. parainfluenzae was resistant to tetracyclines (63.3%), ceftriaxone/fluoroquinolones (46.7%); 40.0% met the criteria for multidrug resistance (MDR) and 20.0% extensively drug-resistant (XDR), with susceptibility retained only to ertapenem among the tested isolates; H. influenzae resistance was rare.

Haemophilus spp., particularly H. parainfluenzae, accounted for nearly 10% of urethritis cases, supporting its likely pathogenic role. High MDR/XDR rates raise concerns for treatment and underscore the need for updated antimicrobial stewardship and surveillance.