Trends in Haemophilus influenzae Resistance Over the Past 11 Years: A Tertiary Hospital Experience

This study aimed to evaluate retrospectively the species Haemophilus influenzae (H. influenzae) that was isolated from clinical specimens of patients admitted to our tertiary care hospital January 1, 2014, and December 31, 2024 and to investigate their antimicrobial resistance patterns. H. influenzae was identified using MALDI-TOF MS (Bruker Daltonik GmbH, Bremen, Germany) and serotyped using Difco H. influenzae Type b antiserum (Difco-BD®-USA). Only 21 (1.4%) samples (10 blood, 5 biopsy, 3 CSF, 2 vitreous, 1 pleural) isolated with H. influenzae were from invasive sites, and sputum was the most common sample among non-invasive samples (1179 strains,81%). Ampicillin resistance in H. influenzae isolates was 38.5%. Amoxicillin–Clavulanate (AMC) resistance was 13.5%, cefuroxime resistance was 66.6%, ceftriaxone resistance was 45.7%, chloramphenicol resistance was 12.2%, clarithromycin resistance was 12.7%, erythromycin resistance was 14.3%, levofloxacin resistance was 11.5%, meropenem resistance was 21.2%, rifampicin resistance was 20.2%, tetracycline resistance was 21%, and Trimethoprim–Sulfamethoxazole (TMP-SMX) resistance was 34.3%. Ampicillin and TMP-SMX resistance were statistically more prevalent in non-Type B strains. TMP-SMX resistance was statistically more prevalent in non-invasive samples. Strains from patients in the intensive care unit (ICU) were statistically more resistant to ampicillin and ceftriaxone. As a result, rates of antibiotic resistance for H. influenzae vary over time, depending on the country, and even within regions of the same country. Considering the annual fluctuations in antibiotic resistance, it is important to be aware of the current local drug resistance situation. This study revealed the need to reevaluate treatment options due to high resistance rates of ampicillin, ceftriaxone, cefuroxime, and TMP-SMX for treating infections caused by H. influenzae.