Haemophilus influenzae serotype a meningitis in an elderly patient: A case report and literature review.

Haemophilus influenzae is a gram-negative bacterium that encompasses a diverse group of strains with varying pathogenic potentials. Classified into six serotypes (a-f), it has been historically associated with a range of infections, including respiratory tract infections, bacteremia, meningitis, and others. Of particular significance is H. influenzae type b (Hib), which was a leading cause of invasive diseases in children prior to the introduction of the Hib vaccine. The Hib vaccine has revolutionized the prevention of severe bacterial infections and has drastically reduced the incidence of Hib. Haemophilus influenzae serotype a (Hia) has now emerged as a significant contributor to bacterial meningitis leading to morbidity and mortality. It remains a notable concern among elderly patients, despite its historical association with children. This shift in demographic susceptibility is accompanied by distinct clinical characteristics and challenges in diagnosis. Here we report a case of Hia meningitis and bacteremia in a previously healthy elderly patient, who responded to ceftriaxone treatment. Efforts to address the global burden of Hia meningitis include robust surveillance and potential vaccine development, aiming to mitigate its impact on vulnerable populations.