Hemophilus influenzae type b is a major cause of serious, invasive infections in infants and children. It causes most cases of bacterial meningitis, nearly all cases of epiglottitis, and a substantial number of the cases of bacterial pneumonia, septic arthritis, febrile bacteremia, and facial cellulitis in young children. H influenzae strains causing otitis media and sinusitis are usually nonencapsulated. In spite of advances in the diagnosis and therapy of H influenzae type b infections, the mortality and morbidity remain appreciable. Approximately 3% to 10% of children with H influenzae type meningitis die, and 25% to 50% of survivors are reported to have neurologic sequelae. Epiglottitis is a lifethreatening emergency and may result in sudden, unpredictable airway obstruction. The incidence of H influenzae type b infection is highest during infancy, with the peak between 6 and 12 months of age1 (Table); epiglottitis is an exception; the mean age of occurrence is 44 months.1 Other risk factors include the following: (1) household contact with a patient with invasive H influenzae type b disease2; (2) day care attendance3; (3) functional or anatomic asplenia including sickle cell anemia4; (4) immunosuppression, including patients with Hodgkin disease5; and (5) agammaglobulinemia.6 An increased incidence of invasive H influenzae type b disease has also been reported in certain population groups, such as American Indians,7,8 Alaskan Eskimos,9 and blacks.10 Genetic factors have also been implicated in disease susceptibility.11 CLINICAL STUDIES A vaccine consisting of the purified H influenzae type b capsular polysaccharide has been licensed for use in the United States.
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