Clinical and Molecular Epidemiology of Invasive Haemophilus influenzae Serotype a Infections in Utah Children

Background. Following widespread use of the Haemophilus influenzae serotype b (Hib) vaccine, H. influenzae serotype a (Hia) has emerged as an important pathogen in children in some regions. We describe the clinical features and molecular epidemiology of invasive Hia disease in children in Utah over an 11-year period. Methods. We identified cases of invasive Hia disease, defined as detection of Hia from a normally sterile site, in children aged <18 years from Utah between 2007 and 2017. Medical records were reviewed to determine demographic characteristics and clinical outcomes. Available Hia isolates were genotyped using multilocus sequence typing, and phylogenetic division was determined using sodC polymerase chain reaction. Presence of the putative virulence-associated IS1016-bexA duplication-deletion was evaluated. Results. We identified 51 children with invasive Hia. The average annual incidence was 1.7 cases per 100 000 children aged <5 years; 4.8 cases per 100 000 children aged <1 year. The median age was 11.3 months. The most common clinical presentation was meningitis (53%), followed by pneumonia (14%) and septic arthritis (14%). Twenty-two children (43%) required admission to an intensive care unit; 1 died. Sequence type (ST) 62, phylogenetic division II isolates caused 75% (21/28) of disease. No isolates contained the virulence-associated IS1016-bexA duplication-deletion. Conclusions. Hia is a significant cause of severe invasive bacterial infection in Utah. The majority of infections were caused by ST62 isolates, a phylogenetic division II Hia type that lacks the IS1016-bexA duplication-deletion. Hia ST62 has not been commonly reported elsewhere, suggesting a unique molecular epidemiology in our population.