Impact of Haemophilus influenzae Type B Vaccination on Nasal Carriage of Haemophilus influenzae in Children under Five (5) Years of Age in Obio-Akpor LGA, Nigeria

Abstract

Background: Haemophilus influenzae type b (Hib) remains an important paediatric pathogen, and Hib-containing vaccines have substantially reduced invasive Hib disease; however, the effect on nasopharyngeal carriage and concurrent antimicrobial resistance patterns remains relevant for ongoing surveillance in Nigeria, where the pentavalent (Hib-containing) vaccine was introduced into routine immunisation in 2012. Aim: This study assessed the impact of Hib vaccination on nasal carriage of Haemophilus influenzae among children aged five (5) years or less in Obio-Akpor Local Government Area, Nigeria, and described the antimicrobial susceptibility patterns of nasal bacterial isolates, with molecular evaluation of selected samples. Methodology: A cross-sectional study was conducted among 198 children. Nasal swabs were processed using conventional culture and biochemical identification methods, antimicrobial susceptibility testing was performed using the Kirby–Bauer disc diffusion method in line with CLSI 2021 guideline, and molecular analysis (PCR) was conducted on 30 nasal samples. Data were analysed using GraphPad Prism 9, with statistical significance set at p < 0.05. Results: Culture yielded no H. influenzae isolates; instead, Staphylococcus aureus (44.4%) predominated, followed by Corynebacterium species (26.3%), Staphylococcus epidermidis (7.1%), and alpha-haemolytic Streptococcus (6.1%). PCR detected H. influenzae DNA in 7 (23.3%) of 30 samples despite negative cultures. Antimicrobial susceptibility testing showed widespread multidrug resistance across nasal isolates, with Augmentin resistance of 2 (100.0%), 19 (100.0%), 55 (100.0%), and 9 (100.0%) among alpha-haemolytic Streptococcus (N = 2), Corynebacterium spp. (N = 19), S. aureus (N = 55), and S. epidermidis (N = 9), respectively, and similarly high resistance to multiple cephalosporins and other agents; cefoxitin resistance was particularly high in S. aureus (50 (90.9%)). In contrast, meropenem resistance was 0 (0.0%) across all isolates, while levofloxacin resistance was variable, including 30 (54.5%) in S. aureus and 1 (11.1%) in S. epidermidis. Conclusion: H. influenzae carriage may persist at levels not detectable by culture in this setting, supporting the integration of molecular methods into carriage surveillance, while the observed resistance patterns among common nasal isolates highlight the need for strengthened antimicrobial stewardship and continued monitoring of community antimicrobial resistance.