Pediatric invasive Haemophilus influenzae infections in Israel in the era of Haemophilus influenzae type b vaccine: a nationwide prospective study

Abstract

Background: The conjugated Haemophilus influenzae (Hi) type b vaccine caused a marked decrease in invasive Hi disease rates. Nonencapsulated Hi infection now constitutes most invasive Hi morbidity and mortality. This study examines invasive Hi infection incidence in Israel in the postvaccine era years, 2003-2012, and characterizes the epidemiology, clinical diagnosis and case fatality rates of invasive Hi disease in children <15 years of age.

Methods: An ongoing, nationwide prospective surveillance program for invasive Hi infections in Israel. Epidemiologic and clinical data were collected. Diagnoses were classified as meningitis, pneumonia, bacteremia/sepsis and other clinical foci.

Results: Overall, 389 cases of invasive Hi infections were identified; 242 (62%) nontypable Hi (NTHi), 103 (26%) Hi type b (Hib) and 41 (11%) encapsulated non-b Hi (enbHi). Children <1 year of age accounted for 51% of the overall disease. Invasive Hi disease incidence in children <15 years of age was stable with a mean annual incidence (per 100,000) of 2.0 ± 0.4. The highest incidence of invasive Hi infections was among infants <1 year with rates of 6.2, 4.9, 1.6 and 12.7 for NTHi, Hib, enbHi and total Hi, respectively. The clinical diagnoses of NTHi and enbHi were similar, but differed from Hib with the former presenting mostly as isolated sepsis/bacteremia and the latter primarily as meningitis. Among children with invasive Hib infection, 40% were classified as vaccine failure.

Conclusions: In the post-Hib vaccination era, invasive Hi morbidity and mortality are largely attributed to NTHi sepsis. Still, with the changing epidemiology of invasive Hi, continued surveillance of all Hi strains is justified.