The changing epidemiology of invasive bacterial infections in Massachusetts children, 1984 through 1991.

Coincident with the licensure of Haemophilus influenzae b conjugate vaccines from 1987 to 1990, the incidence of meningitis and other invasive infections caused by H influenzae type b declined in Massachusetts children by 87% and 91%, respectively. By 1991, Neisseria meningitidis had replaced H influenzae b as the leading cause of bacterial meningitis, accounting for 57% of cases. During the period 1984 through 1991, serogroup C displaced sero-group B as the most common cause of N meningitidis disease. Streptococcus pneumoniae caused 92% of nonmeningitis invasive disease, with sero-groups 14, 6, 19, 18, 4, 23, and 9 causing 94.5% of infections. These findings have implications for the development of additional polysaccharide-protein conjugate vaccines for the prevention of childhood infections.