Socioeconomic risk factors for invasive Haemophilus influenzae type b disease.

Socioeconomic risk factors for primary invasive Haemophilus influenzae type b (Hib) disease include factors that increase exposure to Hib (day care attendance, presence of siblings, and crowded households) and factors that increase an individual's susceptibility to Hib infections (short duration of breast feeding, parental smoking, and frequent infections in general). These factors are consistently found to be associated with risk of Hib disease in studies conducted in populations that differ in their Hib disease epidemiology. However, there are large differences in the prevalence of these risk factors among populations. According to present knowledge, variations in the prevalence of socioeconomic risk factors may explain most of the differences in the epidemiology of Hib disease and may also contribute to the differences in Hib vaccine efficacy in different populations.