Serotype distribution of Streptococcus pneumoniae infections among preschool children in the United States, 1978-1994: implications for development of a conjugate vaccine.

Conjugation of pneumococcal polysaccharide antigens to a protein carrier may improve protective immunity after vaccination of young children, an age group with high incidence of Streptococcus pneumoniae infection and poor immune responses to polysaccharide vaccines. To identify serotypes most commonly associated with infection in young children, pneumococcal isolates were serotyped from 3884 children < 6 years old (including 3007 < 2 years old) with pneumococcal bacteremia (n = 3169), meningitis (n = 401), or otitis media (n = 314). The isolates were submitted as part of a national surveillance during 1978-1994. Seven serotypes (14, 6B, 19F, 18C, 23F, 4, and 9V) accounted for 3045 isolates (78%). A conjugate pneumococcal vaccine protecting against these seven serotypes and serologically cross-reactive serotypes could potentially prevent 86% of bacteremia and 83% of meningitis but only 65% of otitis media cases. The proportion of isolates covered by such a vaccine increased from 78% to 87% during 1978-1994. Surveillance for pneumococcal serotypes causing infection is needed to detect shifts in serotype distribution over time.