Objective.-To document trends in the incidence of invasive Haemophilus influenzae diseases in young children of US Army active duty soldiers following the publication of H influenzae type b immunization recommendations for young children between 1985 and 1990. Design.-A population-based surveillance of hospital discharge diagnoses for H influenzae invasive diseases. Setting.-Military and civilian medical treatment facilities around the world. Patients.-There was a mean population of nearly 200 000 US Army health care beneficiaries younger than 5 years of age each year of the study. Outcome Measures.-Annual total and age-specific incidences of the six most common H influenzae invasive diseases in this population (meningitis, epiglottitis, septicemia, pneumonia, cellulitis, and septic arthritis). Results.-The annual number of cases of H influenzae invasive diseases decreased from a high of 188 in 1986 to 43 in 1991. The incidence in the age group at highest risk for H influenzae disease, those 6 to 11 months of age, decreased from 355 per 100 000 children in 1986 to 116 per 100 000 in 1991 (P<.0001, chi2 for trend). The incidence for H influenzae meningitis declined from 59 per 100 000 children in 1986 to 6 per 100 000 in 1991 (P<.0001, chi2 for trend). Conclusions.-The decrease in H influenzae invasive diseases closely follows the dates of H influenzae type b vaccine licensure for use in progressively younger age groups. Some age groups, however, experienced a decline in disease rates even before becoming eligible for vaccination.
