Interaction of the heptavalent pneumococcal conjugate vaccine and the use of individual antibiotics among children on nasopharyngeal colonization with erythromycin-resistant Streptococcus pneumoniae

The purpose of this study was to assess the complex interaction of the heptavalent pneumococcal conjugate vaccine (PCV7) and individual classes of antimicrobial agents on the nasopharyngeal carriage of erythromycin-resistant pneumococci within the day-care center population. Between February 2005 and May 2007, nasopharyngeal cultures for Streptococcus pneumoniae were obtained from 1,829 day-care center attendees in Central Greece. Thirty-one percent of the pneumococci were erythromycin-resistant; 85.2% of these isolates were also penicillin-nonsusceptible. PCV7 immunization was associated with decreased carriage of erythromycin-resistant PCV7 serotypes but not with an overall decrease in erythromycin-resistant S. pneumoniae colonization. The largest decline in the carriage of erythromycin-resistant pneumococci, particularly of PCV7 serotypes, was observed among vaccinated attendees who had not been exposed to antimicrobials within the preceding 3 months. Exposure to macrolides, 90% clarithromycin, significantly correlated with erythromycin resistance (adjusted odds ratio [AOR] = 2.08, 95% confidence interval [CI] = 1.38-3.12). There was a trend toward an association between the use of oral cephalosporins, other than cefprozil and cefaclor, and colonization with erythromycin-resistant pneumococci (AOR = 1.91, 95% CI = 0.92-3.96). Penicillins had a nonsignificant correlation with the carriage of erythromycin-resistant pneumococci (AOR = 1.17, 95% CI = 0.80-1.71). Despite the widespread PCV7 immunization, the antibiotic pressure, particularly of macrolides, continues to cause dissemination of erythromycin-resistant, commonly multidrug-resistant, pneumococci within the day-care center population.