Surveillance of epidemiological characteristics and temporal trends in antimicrobial resistance of Haemophilus influenzae in pediatric lower respiratory tract infections (2021–2024)

This study investigated the clinical characteristics of Haemophilus influenzae (Hi) infections in the lower respiratory tract of pediatric patients in the southwestern Shandong Province, China, aiming to improve early diagnosis and guide clinical management. This retrospective cohort study analyzed pediatric patients with Hi lower respiratory tract infections in southwestern Shandong Province, China. Clinical isolates were obtained through standardized sputum/bronchoalveolar lavage collection protocols and underwent microbiological identification, antimicrobial susceptibility testing, and β-lactamase production detection. All eligible pediatric patients with microbiologically confirmed lower respiratory tract infections during the study period were included, with no additional selection applied.The epidemiological patterns and clinical characteristics were systematically evaluated using electronic medical record data covering the period from January 2021 to December 2024. During the 4-year monitoring period (2021-2024), Hi was isolated from 1028 cases of lower respiratory tract bacterial infections in children, with an overall detection rate of 13.00%. The highest detection rate was observed in children aged 1-3 years (27.23%) and during the first quarter (17.37%, p < 0.05). Single-pathogen infections predominated (83.95%), while polymicrobial infections (16.05%) mainly involved Staphylococcus aureus and Streptococcus pneumoniae. Levofloxacin showed 100% susceptibility. High susceptibility rates (> 93%) were also observed for ciprofloxacin (99.71%), imipenem (99.51%), meropenem (98.74%), ceftriaxone (94.75%), ceftazidime (94.55%), cefotaxime (94.46%), and chloramphenicol (93.29%). Low susceptibility was observed for sulfamethoxazole-trimethoprim (34.73%). Susceptibility to ampicillin and cefuroxime showed significant downward trends (ampicillin: 10.45% in 2021 to 2.13% in 2024, p < 0.001; cefuroxime: 21.82% in 2021 to 7.18% in 2024, p < 0.001). β-Lactamase was produced by 86.28% of isolates, and BLNAR strains accounted for 7.10%. Decreased sensitivity to ampicillin and cefuroxime was observed, alongside sustained low sensitivity to sulfamethoxazole-trimethoprim. Third-generation cephalosporins, carbapenems, and fluoroquinolones remain highly sensitive in vitro. These findings support avoiding ampicillin and cefuroxime in empirical treatment and underscore the need for ongoing resistance surveillance and optimized pediatric antimicrobial stewardship.