Epidemiology of Haemophilus influenzae type b disease in Australia and New Zealand.

The epidemiology of infection due to Haemophilus influenzae type b (Hib) varies in different groups of Australian and New Zealand children. In most populations the annual case attack rate is approximately 40-60 per 100,000 children under 5 years of age and epiglottitis accounts for a relatively high but variable proportion of cases, which partly depends on case definition. Overall, nearly 50% of cases occur in children over 2 years of age. Among Aboriginal children in the Northern Territory, the epidemiology is strikingly different. The annual case attack rate is approximately 450 per 100,000 children under 5 years and varies in different geographical areas. Most cases occur in the first year of life (40% at less than 6 months) and epiglottitis is rare. The case attack rate in non-Aboriginal children in the Northern Territory (88 per 100,000) is significantly less than in Aboriginal children but higher than elsewhere. The differences between Maori and Caucasian children in New Zealand are less marked. Different immunization strategies may be required for children in different populations within Australia and New Zealand.