Nasopharyngeal Carrier Rate of Streptococcus pneumoniae in Children: Serotype Distribution and Antimicrobial Resistance

Background: This study aimed to define the nasopharyngeal carrier rates, serotype distribution, and antimicrobial resistance patterns of Streptococcus pneumoniae in healthy children less than ten years-old in Tehran. Methods: This was a cross-sectional study conducted from November 2008 until January 2009. Nasopharyngeal specimens were collected by trained investigators from 1300 healthy children recruited from 20 randomly selected day care centers and 50 elementary schools in Tehran and inoculated into blood agar. Positive cultures that grew alpha-hemolytic colonies were gram-stained and serotypes of the isolates identified by the Quellung reaction. All isolated pneumococci were tested for sensitivity to different antibiotics by the disc diffusion method. Results: The carrier rate for Streptococcus pneumoniae was 44.1%. Serotypes 19, 6, 14, 17, 20, 23, and 21 were most common, found in decreasing order from 11.9% to 6.1%. Only 38.56% of isolates belonged to strains covered by the heptavalent pneumococcal vaccine. Most (69.4%) were resistant to one or more antimicrobial agents: tetracycline (69.85%), clarithromycin (57.2%), azithromycin (54.9%), cotrimoxazole (11.8%), penicillin (9.2%), and vancomycin (1.5%). All isolates were sensitive to rifampin and meropenem. Conclusion: This study has revealed the nasopharyngeal carrier rate, serotype distribution and antibiotic sensitivities of Streptococcus pneumoniae strains in children from Tehran. Our findings may have implications on the type and efficacy of pneumococcal conjugate vaccines that should be used for prevention of pneumococcal invasive disease in Iranian children.