Nasopharyngeal colonization and antimicrobial resistance of Streptococcus pneumoniae isolated from children with acute rhinopharyngitis

Abstract

Objective: to determine the prevalence and risk factors for nasopharyngeal colonization by, and to evaluate antimicrobial susceptibility of Streptococcus pneumoniae strains in children with acute rhinopharyngitis. Methods: we collected nasopharyngeal swab specimens from 400 children aged 3 months to 5 years and with clinical status of acute rhinopharyngitis from June 16, 1997 to May 20, 1998 at the outpatient clinics of two hospitals in the city of São Paulo. Nasopharyngeal specimens were collected pernasally using a calcium alginate swab and plated immediately after collection onto trypticose soy agar with 5% sheep blood and garamicin 5 mcg/ml. Penicillin susceptibility was determined by oxacillin 1 mcg disk screening test and the minimal inhibitory concentration by the E-test. Results: Pneumococci were recovered from 139 children, indicating a colonization prevalence of 35%. The risk factors analyzed indicated that the colonization was more prevalent in children attending day-care centers, children with siblings younger than 5 years, and children with recent use of antimicrobial agents. The prevalence of penicillin non-susceptible strains was of 16% (20 strains). All strains were intermediately resistant (0.1 mcg/ml ≤ MIC ≤ 1.0 mcg/ml). Out of the penicillin intermediately resistant strains, 7 (37%) showed intermediate resistance to cotrimoxazol and 2(11%) full resistance to trimethoprim-sulfamethoxazole. No strains were resistant to ceftriaxone, amoxicillin, clarithromicin, or chloramphenicol. Conclusions: our findings indicate that the prevalence of nasopharyngeal colonization by Streptococcus pneumoniae in children with upper respiratory infections was of 34.8%. Children attending day-care centers and children with younger siblings showed higher levels of colonization The results of prevalence of bacterial resistance were similar to those of studies regarding invasive infections, thus indicating that nasopharyngeal isolates of Streptococcus pneumoniae can be used in the surveillance of antimicrobial resistance in a defined geographical area.