Epidemiology and prevention of invasive Haemophilus influenzae type b infection

The use of rifampicin prophylaxis is recommended in close contacts of individuals with invasive Haemophilus influenzae type b infection if they include a child less than 4 years old in whom the risk of secondary infection is relatively high. In practice, delays in administration of rifampicin, contra-indications to its use and the difficulty of identifying all contacts at risk can reduce significantly its efficacy. Only 1-2% of cases of H. influenzae type b diseases are attributable to known contact and, at best, rifampicin prophylaxis can have little impact on the incidence. In the USA, one in 200 children less than 5 years old is affected. The incidence is probably similar in Australia but there are local differences which could affect the value of preventative measures. The vaccine recently licensed in the USA is not effective in children less than 18-24 months of age in whom the incidence of invasive H. influenzae type b infection, other than epiglottitis, is highest. Nevertheless, it could prevent more than 30% of cases if given to children at the age of 24 months. Vaccines effective in younger infants should become available soon. The best chance of prevention is by the optimal use of both rifampicin prophylaxis and immunization.