Invasive Haemophilus influenzae disease among adults in Japan during 2014–2018

Purpose We describe the epidemiology of invasive Haemophilus influenzae disease (IHD) among adults in Japan. Methods Data for 200 adult IHD patients in 2014–2018 were analyzed. The capsular type of H. influenzae was determined by bacterial agglutination and polymerase chain reaction (PCR), and non-typeable Haemophilus influenzae (NTHi) was identified by PCR . Results The annual incidence of IHD (cases per 100,000 population) was 0.12 for age 15–64 years and 0.88 for age ≥ 65 years in 2018. The median age was 77 years, and 73.5% were aged ≥ 65 years. About one-fourth of patients were associated with immunocompromising condition. The major presentations were pneumonia, followed by bacteremia, meningitis and other than pneumonia or meningitis (other diseases). The case fatality rate (CFR) was 21.2% for all cases, and was significantly higher in the ≥ 65-year group (26.1%) than in the 15–64-year group (7.5%) ( p = 0.013). The percentage of cases with pneumonia was significantly higher in the ≥ 65-year group than in the 15–64-year group ( p