Trends in the epidemiology of invasiveHaemophilus influenzaedisease in Queensland, Australia from 2000 to 2013: what is the impact of an increase in invasive non-typableH. influenzae(NTHi)?

Abstract

SUMMARYFollowing the introduction of vaccination againstHaemophilus influenzaetype b (Hib), cases of invasive encapsulated Hib disease have decreased markedly. This study aimed to examine subsequent epidemiological trends in invasiveH. influenzaedisease in Queensland, Australia and in particular, assess the clinical impact and public health implications of invasive non-typableH. influenzae(NTHi) strains. A multicentre retrospective study was conducted from July 2000 to June 2013. Databases of major laboratories in Queensland including Queensland Forensic and Scientific Services (jurisdictional referral laboratory for isolate typing) were examined to identify cases. Demographic, infection site, Indigenous status, serotype, and mortality data were collected. In total, 737 invasive isolates were identified, of which 586 (79·5%) were serotyped. Hib, NTHi and encapsulated non-b strains, respectively, constituted 12·1%, 69·1% and 18·8% of isolates. The predominant encapsulated non-b strains were f (45·5%) and a (27·3%) serotypes. Of isolates causing meningitis, 48·9% were NTHi, 14·9% Hib, 14·9% Hie, 10·6% Hif, 6·4% Hia and 4·3% were untyped. During the study period, there was an increase in the incidence of invasive NTHi disease (P= 0·007) with seasonal peaks in winter and spring (P< 0·001). The incidence of Hib disease (P= 0·295) and of encapsulated non-b disease (P= 0·122) did not change significantly. Highest overall incidence was in infants, Indigenous, and elderly patients. Australian Indigenous patients were more likely to have Hia (P> 0·001) and Hib (P= 0·039) than non-Indigenous patients. In Queensland, invasiveH. influenzaedisease is now predominantly encountered in adults and most commonly caused by NTHi strains with demonstrated pathogenicity extending to otherwise young or immunocompetent individuals. Routine public health notification of these strains is recommended and recent available immunization options should be considered.