Decrease of invasive pneumococcal infections in children among 8 children's hospitals in the United States after the introduction of the 7-valent pneumococcal conjugate vaccine

Objective. To monitor clinical and microbiologic features including antimicrobial susceptibility and serogroup distribution of invasive infections caused by Streptococcus pneumoniae among children before and after the introduction of routine administration of the 7-valent pneumococcal conjugate vaccine (PCV7). Design. A 9-year ( January 1, 1994 through December 31, 2002) prospective surveillance study of all invasive pneumococcal infections in children. Patients. Infants and children cared for at 8 children's hospitals in the United States with culture-proven invasive infections caused by S pneumoniae. Results. When compared with the mean of the years 1994 to 2000, the annual number of invasive pneumococcal infections for children less than or equal to 24 months of age declined 58% in 2001 and 66% in 2002. If only the serogroups in the PCV7 are considered, the number of cases in children less than or equal to 24 months old declined 63% and 77% in 2001 and 2002, respectively. The greatest decrease was observed for serogroup-14 isolates. The number of isolates in nonvaccine serogroups increased 28% in 2001 and 66% in 2002 for children less than or equal to 24 months old. Nonvaccine serogroup-15 and - 33 isolates had the greatest increase in number. The proportion of all isolates nonsusceptible to penicillin increased yearly from 1994 to 2000, reached a plateau in 2001 at 45%, and declined to 33% in 2002. Decrease in nonsusceptibility to penicillin occurred entirely in the isolates with penicillin minimum inhibitory concentration greater than or equal to 2 mug/mL. Nonsusceptibility to penicillin increased slightly among nonvaccine-serotype isolates. Most infections after at least 2 doses of PCV7 were caused by nonvaccine-serotype isolates. Conclusions. Since the introduction of the PCV7, the number of invasive pneumococcal infections caused by vaccine-serogroup isolates among 8 US children's hospitals has decreased > 75% among children less than or equal to 24 months old. In addition, penicillin resistance decreased in 2002 for the first time since our surveillance began in 1993 1994. However, we have noted that replacement may be developing with serogroups 15 and 33. Furthermore, penicillin resistance seems to be increasing among nonvaccine serogroups. Surveillance must be continued to detect the emergence of changes in the distribution of serotypes as well as antibiotic susceptibility.