Epidemiology of invasive Haemophilus influenzae type b disease in Scandinavia

In all Scandinavian countries, most invasive Haemophilus influenzae type b (Hib) infections occur before the age of 5 years. The age-specific incidence of Hib meningitis in this age group is 26-35/100,000 per year in Denmark, Norway, Finland and Sweden and about 43/100,000 per year in Iceland. Of the meningitis patients, approximately 60% are younger than 2 years but Hib meningitis also occurs in older children and adults. The case fatality rate is low (1-3%) in children but the rate of neurological sequelae is considerable. The incidence of acute epiglottitis, the other main manifestation of Hib disease, varies considerably. In Sweden, four studies have shown a very high incidence in the age group 0-4 years, 21-34 cases/100,000 population per year compared to only 5-17 in the other Nordic countries. Epiglottitis is more common than Hib meningitis in older children and adults. In Scandinavia the age-specific incidence of all invasive Hib infections could be estimated to be about 50-65/100,000 per year in the most susceptible age group and the risk of contracting invasive Hib disease before the age of 15 years would be about 1/200-300 children.