The epidemiology of invasive Haemophilus influenzae in Northwestern Ontario from 2021 to 2022

Invasive Haemophilus influenzae disease, particularly caused by serotype a (Hia) and non-typable (NTHi) strains, is prevalent in northwestern Ontario, Canada and can cause serious illness. This study reviewed epidemiological data for seven cases of invasive H. influenzae disease that presented over a 20-month period at the regional hospital serving northwestern Ontario. One pediatric and six adult cases with the following blood isolates were reported: 2 Hia, 2 NTHi, 2 serotypes f (Hif) and 1 serotype e (Hie). These findings demonstrate the consistent presence of Hia and NTHi as causes of serious disease in the region, preferentially affecting adults. Most patients in this cohort presented with pneumonia (71.4%) or bacteremia (57.1%). Two unique adult cases, bacteremia caused by Hie and epiglottitis secondary to Hif, were reported. This study highlights the need for ongoing surveillance of invasive H. influenzae disease in the region. The continuing presence of Hia supports introducing a new Hia vaccine, which is undergoing clinical trials in Canada, for immunization of groups at risk of invasive Hia disease.