Clinical and microbiological characteristics of invasive diseases due to Haemophilus influenzae in the Minami Ibaraki Area, Japan.

Introduction: We investigated clinical and microbiological characteristics of invasive Haemophilus influenzae disease (IHD) during recent 20 years in the Minami Ibaraki Area.

Methods: H. influenzae strains isolated from the blood and the cerebrospinal fluid in 5 hospitals located in this area between 2001 and 2020 (the pre-vaccination period [PreVP]: 2001-2010, the post-vaccination period [PostVP]: 2011-2020) were consecutively collected. Drug susceptibilities, capsular types, β-lactamase production, and sequence types of the strains and clinical information of patients from whom the strains were isolated were investigated.

Results: A total of 99 H. influenzae strains (59 in PreVP and 40 in PostVP) were collected. The ages of the patients were significantly higher in PostVP (median: 1 vs 69.5 years). The most common organ infected primarily was the central nervous system in PreVP (38 cases) and the lung in PostVP (22 cases). Mortality was significantly higher in PostVP (1.7% vs 15.0%). Strains serotyped b (Hib) and non-typeable (NTHi) were predominant in PreVP and PostVP (88.1% and 80.0%, respectively). Only 2 encapsulated non-Hib strains (1 each of types e and f) were found. The ratio of strains with beta-lactamase non-producing ampicillin resistance (BLNAR) was significantly higher in PostVP (10.2% vs 42.5%). All Hib strains belonged to the ST6-complex; while most of NTHi strains were genetically diverse.

Conclusion: The picture of IHD in this area has changed from meningoencephalitis among children due to Hib to pneumonia among adults due to NTHi, with the increases in BLNAR strains and mortality.