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To determine the risk of severe Haemophilus influenzae illness among household contacts of patients with H. influenzae meningitis, we studied prospective data obtained in 19 states from January 1, 1977, to June 30, 1978. H. influenzae meningitis was reported in 1403 patients, and 1147 (82 per cent) of the exposed families were investigated for the occurrence of H. influenzae disease within 30 days after its onset in the index patient. During this interval, nine of 1687 household contacts (0.5 per cent) under the age of six years had systemic disease confirmed to be caused by H. influenzae Type b. The risk in children less than one year of age was 6 per cent, and the risk in those less than four years of age was 2.1 per cent. None of 2624 contacts above the age of five was affected. In the 30 days after onset of meningitis, the risk of this infection alone, aside from other types of serious H. influenzae disease, is 585 times greater in household contacts than the age-adjusted risk in the general population. The risk of H. influenzae disease in household contacts under six years of age is similar to the risk of secondary meningococcal disease in all household contacts--indicating a need for effective antimicrobial prophylaxis.

To determine the risk of severe secondary illness in household contacts of patients with Haemophilus influenzae meningitis, telephone interviews were conducted with contacts of patients with reported cases. Four probable or proved secondary cases of severe disease were identified for a secondary attack rate of 0.4%. The secondary attack rate for household contacts of patients 2 years of age and younger was 4.9%. Until safe, effective prophylactic measures become available, physicians should explain to parents that any person who becomes ill in the month after a household case of H influenzae meningitis should be brought to the attention of a physician for appropriate evaluation and treatment.

During 1971-77 the incidence of bacterial meningitis among Alaskan Eskimos was 84.4 cases per 100 000 population per year, which is more than 10 times that for most other U.S. populations. Haemophilus influenzae (HI) accounted for 68% of meningitis cases. The average annual incidence of HI disease per 100 000 children below 5 years of age was 409 for patients with meningitis only and 491 for patients with all systemic HI disease. Children with HI meningitis in Alaska tended to be younger than those in other U.S. populations, 98% of the children affected being less than 18 months of age. The risk for all HI disease was 2.4% during the first year of life. The spectrum of HI disease in Alaska differs from that in other populations in that no patient had epiglottitis and 5% of children had recurrent HI disease. Alaskan newborns and children over 4 years old had HI anticapsular antibody titres that were nearly thrice those for children of similar ages in other U.S. populations (p less than 0.005). The pharyngeal carriage of HI type b (5%) and the rectal carriage of Escherichia coli K100 (2%), an organism with a capsule antigenically similar to HI type b, did not differ from those in other populations. The high incidence of disease almost exclusively in the very young and the early development of antibody in this population suggest that the high rate of disease is due to early exposure to HI type b rather than to an unusual susceptibility to HI type b.