The families of 126 consecutive patients with Haemophilus influenzae type B meningitis were surveyed for secondary invasive H influenzae disease among household contacts. A total of 120 of the families were contacted. In six cases no contact was possible and the medical record was reviewed. Some 555 household contacts were found; 31% (171) were under 5 years of age. A secondary case was defined as a household contact with H influenzae type B isolated from blood or cerebrospinal fluid more than 24 hours, but less than 30 days, after admission to hospital of the index case. Four secondary cases were identified, all in children aged under 5 years. The secondary attack rate in children under 5 years or less in the month after exposure to an index case was thus 2.3%, 800 times the endemic attack rate for H influenzae meningitis. This is a conservative estimate since five additional contact cases were documented, but not included in the secondary attack rate. Young contacts of a child with H influenzae meningitis are thus at significant risk of life-threatening secondary disease.
