Characteristics of 241 invasive and non-invasive Haemophilus influenzae isolated from patients under 14 years old, Hebei Province, China.

Background: The introduction of the Haemophilus influenzae type b (Hib) vaccine has led to significant variations in the epidemiological patterns of H.influenzae globally, with regional differences. However, large sample pathogenetic studies and comparative analyses of H.influenzae in China remain limited, especially in Hebei Province. This study aimed to characterize the patterns in serotypes and the antimicrobial resistance of invasive and non-invasive H.influenzae in children under 14 years of age in Hebei Province.

Methods: An observational study was conducted from January 2019 to December 2021 at Hebei Children's Hospital. H.influenzae was identified using classical biochemical methods, MALDI-TOF MS and hpd gene-based qPCR. Slide agglutination serotyping and molecular capsular typing determined the capsular types. Antimicrobial resistance was tested with the broth dilution method and Kirby-Bauer disk diffusion method, and β-lactamase production was detected using nitrocefin disks.

Results: Among 241 H.influenzae isolates, 13 were invasive and 228 were non-invasive. The proportion of invasive isolates differed significantly across age groups (P = 0.005), i.e., 14.55% among patients < 1 year of age, 0.00% among 1-2 years of age, 4.26% among 3-5 years of age, and 2.33% in the 6-13 age groups. Three capsular types were detected: Hib (10/241), Hie (2/241), and Hif (7/241), with 222 isolates identified as NTHi. Hib accounted for 61.54% of the invasive isolate. Antimicrobial susceptibility tests also showed that invasive isolates exhibited higher nonsensitivity to cefuroxime, ceftriaxone, cefepime, imipenem, meropenem, and clarithromycin compared to non-invasive isolates (P < 0.05). The percentage of BLNAI and BLNAR was also higher for invasive isolates than in non-invasive ones (46.15% vs. 20.61%, P = 0.042).

Conclusions: Although NTHi is becoming the predominant pathogen of H.influenzae infection in children under 14 years, Hib remains the leading cause of invasive infection in Hebei Province. The high prevalence of β-lactamase-producing and BLNAR isolates underscores a growing challenge in antimicrobial resistance, particularly among invasive isolates.