Serotyping, Antibiotic Susceptibility and Related Risk Factors As¬pects of Nasopharyngeal Carriage of Streptococcus pneumoniae in Healthy School Students

Streptococcus pneumoniae is an important problem worldwide and nasopharyngeal colonization plays significant role in pneumococcal infections. The aims of this study were to determine the nasopharyngeal colonization rate, serotyping, antibiotics susceptibility and study the risk factors for nasopharyngeal colonization with S. pneumoniae in students in Kashan, Iran. A cross-sectional study was conducted on children aged 7 to 19 years from December 2011 to November 2012. Nasopharyngeal swabs were plated onto brain heart infusion agar plates with 5% sheep blood and 4μg/ml of gentamycin. Antimicrobial susceptibility profiles were determined on Mueller-Hinton agar in accordance with CLSI. S. pneumoniae strains were investigated for the presence of the most common pneumococcal serotypes using a multiplex polymerase chain reaction. 13.9% were found to be carriers. The most prevalent serogroups were 19F (30%), 6A/B (18.9%), 15A (16.5%), 11 (11.3%), 23F (8.2%), 1 (6.2%), 19A (3.4%), and 35B (2.4%). Nine strains (3.1%) were non-typeable. The carrier rate was significantly higher in 12 to15 year old age group. Upper respiratory tract infections within the last month (OR=1.5, P<0.011), previous hospitalization (OR=1.6, P<0.001), previous antibiotic usage last two weeks (OR=1.89, P<0.001), rhinorea (OR=1.9 P<0.001), male sex (OR=3.5 P< 0.001) and passive smoking (OR=1.56, P< 0.001) have been determined to be risk factors for S. pneumoniae carriage. The highest pneumococcal resistance was to tetracycline (25.4%). All strains were susceptible to linezolid and levofloxacin. Our information leads to an important source to screen the future impact of pneumococcal vaccination on bacterial colonization.