Haemophilus influenzae serotype a as a cause of purulent meningitis in a six-month-old infant.

Haemophilus influenzae serotype b (Hib) has historically been the most significant pathogen causing invasive infections. In recent decades, an increase in the incidence of other Haemophilus influenzae serotypes has been observed, particularly serotypes e+ f, as well as, most notably, invasive infections caused by non-typeable strains. Invasive disease caused by Hia, similarly to Hib, affects primarily young children and represents a significant cause of morbidity and mortality. To better understand the clinical and epidemiological characteristics of Hia, epidemiological studies and active microbiological surveillance of invasive disease across all age groups worldwide are needed. We describe a six-month-old, previously healthy but incompletely vaccinated infant who was hospitalized with suspected sepsis and purulent meningitis following a four-day history of intermittent fever associated with chills, vomiting, drowsiness progressing to apathy, and gradual development of dehydration. Haemophilus influenzae was confirmed from both blood culture and cerebrospinal fluid, and capsular antigen identification at the National Reference Laboratory for Haemophilus infections determined serotype a (Hia). A two-week course of parenteral antibiotic therapy with cefotaxime led to recovery without significant neurological complications.