Invasive Haemophilus Influenzae Infection in Children: Clinical Characteristics, Serotypes and Outcome

Background: Haemophilus influenzae remains an important cause of invasive bacterial infections in children despite widespread vaccination against H. influenzae type b (Hib). In recent years, changes in epidemiology and the emergence of non-Hib serotypes have been increasingly reported worldwide. This study aimed to describe the epidemiology, serotype distribution, clinical characteristics and outcomes of invasive H. influenzae infections among children in Oman. Methods: We conducted a multicenter retrospective study across 5 tertiary and secondary hospitals in Oman between January 2010 and June 2024. Children younger than 13 years with microbiologically confirmed invasive H. influenzae infection from sterile body sites (including cerebrospinal fluid, blood, pleural fluid, peritoneal fluid or synovial fluid) were included. Demographic, clinical, microbiological, vaccination and outcome data were extracted from electronic medical records. Incidence trends, serotype distribution and clinical outcomes were analyzed. Results: A total of 142 children with invasive H. influenzae infection were identified. The median age was 12 months, and infants under 1 year accounted for 45.1% of cases. Males represented 62.7% of patients. The most common clinical presentations were bacteremia (51.4%), meningitis (22.5%) and pneumonia (11.9%). The incidence increased significantly from 0.60 per 100,000 children in 2017 to 2.43 per 100,000 in 2023 (rate ratio 4.05, P = 0.016). Among typed isolates, serotype b was the most frequent (29.6%), followed by nontypeable strains (17.6%) and serotype a (16.9%). Neurological complications occurred in 53.1% of meningitis cases, and seizures at presentation were significantly associated with poor neurologic outcomes ( P = 0.0066). Most children had received 3 doses of Hib-containing vaccine. Overall outcomes were favorable, with 89.4% recovering without sequelae. Conclusion: Invasive H. influenzae infection continues to affect children in Oman despite high vaccination coverage. The observed postpandemic increase and the presence of non-b serotypes highlight the need for ongoing surveillance, improved serotyping capacity and evaluation of vaccination strategies to mitigate future disease burden.