Epidemiology of invasive Haemophilus influenzae non-B in Newfoundland and Labrador: A retrospective case series of a clonal outbreak of serotype A (ST-23), 2020–2022

Background: Haemophilus influenzae (Hi) is a gram-negative coccobacillus that can cause invasive disease.Although the type B vaccine has considerably reduced Hi type B incidence, non-B serotypes have emerged, disproportionately affecting Indigenous populations.Between 2020 and 2022, an increased incidence of invasive Hi (iHi) was observed in Newfoundland and Labrador (NL).Objective: To describe the incidence of iHi in NL and define risk factors and outcomes.Methods: A retrospective case series of sequential laboratory-confirmed iHi cases was conducted using provincial and national microbiology records.Demographic, clinical and molecular typing data were collected via chart review.Results: Eighteen iHi cases were identified between 2020 and 2022, with an annual incidence ranging from 0.59-1.37cases per 100,000 population.Localized incidence rates in the Labrador Indigenous communities far exceeded the provincial rate and reached peak community rates over 300 per 100,000 in some years.In the iHi cases identified, 11/18 cases (61.1%) were Hi type A (HiA) and 11/16 of the sequenced isolates were multilocus sequence type ST-23.The median age was 58 years.Hypertension and dyslipidemia were present in 61.1% of cases and diabetes in 55.6%.The predominant clinical presentation was bacteremia (72.2%).Seventeen of the 18 cases identified (94.4%) were hospitalized, five (27.8%) required intensive care unit (ICU) admission and two (11.1%)died.Conclusion: An escalating incidence of iHi in NL was identified, with a localized clonal outbreak of iHiA (ST-23) predominately affecting Indigenous communities in Labrador.Severe clinical outcomes highlight the need for HiA vaccine development for target populations.