Preventing Haemophilus influenzae type b disease.

The pathogenesis of Haemophilus influenzae type b (Hib) disease and methods for limiting spread of outbreaks of Hib disease are reviewed. Many strains of H. influenzae are surrounded by an outer polysaccharide capsule; of the six antigenically distinct capsular types, Hib is the predominant cause of such serious infections as meningitis, especially among children younger than five years of age. The age-specific incidence of Hib disease appears to be related to the relatively small concentrations of anti-Hib antibody present in young children. Children younger than 48 months of age who reside in the same house or attend the same day-care center as a child who develops Hib disease appear to be at increased risk for contracting systemic Hib infections. Prophylactic administration of rifampin 20 mg/kg once daily for four days can substantially decrease asymptomatic carriage of Hib in household contacts of the index patient and reduce the incidence of secondary Hib disease. The index patient should also receive prophylactic rifampin therapy before discharge from the hospital; i.v. antibiotics may cure the systemic infection but allow nasopharyngeal colonization to persist. A vaccine formulated from purified Hib capsular polysaccharide confers protection to more than 90% of children vaccinated at a minimum age of 24 months. Other candidates for vaccination include children between the ages of two and five years who attend day-care centers and children with anatomic or functional asplenia or malignancies. The vaccine is not effective in children younger than 18 months of age (who account for 60% of Hib disease in the U.S.); methods to increase vaccine immunogenicity in young infants are being evaluated. Reduction of Hib disease in the U.S. may be possible through widespread use of the new vaccine.