Epidemiology of invasive infections with Haemophilus influenzae type b in the world and in Italy

The incidence of Haemophilus influenzae type b (Hib) disease in the 0-5 years age group has been studied in many countries. In the United States, before the introduction of mass vaccination, the incidence of invasive Hib disease ranged from 7 per 100,000 in the 4-5 years age group to 452 pert 100,000 in the 6-11 months age group. In Europe, the incidence of this disease has been estimated to range from 21 to 60 per 100,000 per year in the 0-5 years age group. Hib infection is mainly transmitted by the respiratory route. Risk factors of the disease include: attending a day-care center, a high number of household members, low socio-economic level, age less than two years, and belonging to certain ethnic groups. Accurate estimates of the incidence of invasive Hib disease do not exist in Italy. Among the 15,601 children participating in the "Progetto Pertosse", a clinical trial for the evaluation of antipertussis vaccines, there occurred six cases of Hib meningitis, one of Hib sepsis, and one of Hib cellulitis. These episodes yield an incidence density of 28.7 per 100,000 person-years in the 2-30 month age group. Incidence data will also need to be collected for children in the 30 months-5 years age group before attempting a cost-benefit analysis with the aim of planning a mass vaccination.