Trends in invasive Haemophilus influenzae serotype b (Hib) disease in England: 2012/13 to 2022/23

Haemophilus influenzae serotype b (Hib) conjugate vaccines have been highly successful in reducing the Hib disease worldwide. Recently, several European countries have reported an increase in invasive Hib disease. We aimed to describe the epidemiology, clinical characteristics, genomic trends, and outcomes of invasive Hib disease over the past 11 years in England.

The UK Health Security Agency (UKHSA) conducts national surveillance of invasive H influenzae disease and hosts a national reference laboratory for confirmation and serotyping. General practitioners are contacted to complete a surveillance questionnaire for confirmed Hib cases. Invasive Hib isolates routinely undergo whole genome sequencing.

During 2012/13-2022/23, there were 6881 invasive H. influenzae infections, of which 5852 (85%) were serotyped; most isolates (4881, 83%) were non-typeable H. influenzae, followed by Hif (591, 10%), Hie (189, 3%), Hib (118, 2%) and Hia (54, 1.0%). The median age for invasive Hib disease was 51 years, and most cases (84%, 99/118) were in adults. Children accounted for 19 cases (16%), including 13 (11%) in <1 year-olds and 6 (5%) in 1-5-year-olds. Bacteraemic pneumonia was the most common diagnosis (66/118, 56%). Hib case-fatality rate was 5.9% (7/118), with the last fatality reported in 2016. Among 64 sequenced strains during 2016/17-2022/2023, most (56/64, 88%) belonged to the CC6 lineage (representing ST6 and single locus variants of ST6).

In England, invasive Hib disease remains rare with no evidence of any increase in incidence and is rarely fatal, affecting mainly adults with underlying conditions, who typically develop pneumonia.