Haemophilus influenzae type b carriage in Indigenous children and children attending childcare centers in the Northern Territory, Australia, spanning pre- and post-vaccine eras

This paper investigates Haemophilus influenzae type b (Hib) carriage in Indigenous children and children attending childcare centres in the Northern Territory of Australia, 1992-2005. More than 10 years after the introduction of the Hib conjugate vaccine, Hib carriage persists in Indigenous children (3.4%, 2003-2005) and children attending childcare centres (0.2%, 2004). This is the first Australian study to examine Hib carriage spanning the pre- and post-vaccination eras. Increasing carriage rates contribute to Hib disease resurgence especially in those with higher disease burdens, such as remote Indigenous Australians, ongoing carriage surveillance provides a sentinel warning system for invasive disease.

Background

Following the introduction of H. influenzae type b (Hib) conjugate vaccine to Australia in 1993 as a three dose (2, 4, 12 month) schedule, the incidence of Hib disease decreased dramatically in children, especially in those aged under 5 years. We investigate Hib carriage in Indigenous children and children attending childcare centres from the Northern Territory (NT) of Australia between 1992 and 2005. We report Hib carriage rates in this well vaccinated population, with previously documented high rates of invasive disease.

Methods

Hib carriage was reviewed in nasopharyngeal or nasal swabs collected between 1992 and 2005; from over 2000 children (61% Indigenous) aged 0-6 years enrolled in 7 otitis media or carriage surveillance studies in the NT.

Results

More than 10 years after the introduction of the Hib conjugate vaccine, Hib carriage persists at low levels, but at a higher rate in Indigenous children (3.4%, 2003-2005) than children attending childcare centres (0.2%, 2004), in the NT of Australia.

Conclusions

This is the first Australian study to examine Hib carriage spanning the pre- and post-vaccination eras. Ongoing carriage surveillance provides a sentinel warning system for invasive disease. This notifies public health professionals of potential invasive disease, creating early warning systems for intervention if Australian Indigenous children or children attending childcare centres are to follow current international trends associated with high rates of carriage preceding invasive disease—despite high vaccination rates. Internationally there is growing concern that increasing carriage rates are the driving force behind Hib disease resurgence especially in those with higher disease burdens, such as remote Indigenous Australians. Changes to the vaccination schedule from PRP-OMPC (PedvaxHIB^®), to PRP-T (2, 4, 6, 12 months) from January 2010—may affect carriage and in time, invasive disease rates. This work is important for national and International comparisons as well as feeding back information to vaccine policy makers of the Hib carriage environment throughout this period.