Resistance, serotypes and “hidden resistant clones” of Streptococcu pneumoniae among children in Beijing

Objective Streptococcus pneumoniae (Sp) has long been one of the most important bacterial pathogen causing pneumonia, meningitis, otitis media, sinusitis, and septicemia. During the recent 2 decades, the resistance of Sp to penicillin has been rapidly increasing in many parts of the world. The authors designed the present study to determine the prevalence of drug resistance among streptococcus pneumoniae carried by children in China, to determine the prevalence of vaccine serotypes among carriage strains and to look for carriage of both susceptible and resistant Sp clones in individual patients. Methods The subjects enrolled 502 patients with upper respiratory infections who were 3 months to 5 years of age attending a general outpatient clinic at Beijing Children′s Hospital from Nov. to Dec.1997. A standardized questionnaire addressing age, symptoms of upper respiratory infections, recent antimicrobial use, breastfeeding, day care attendance, household size, smoke exposure, and parental education was completed for all the cases. Nasopharyngeal specimens and urine were collected for culture and antimicrobial activity, respectively. Sp was identified by optochin sensitivity and bile solubility. Sp serotyping was performed by using quelling reaction. Sensitivity to penicillin, cefuroxime, co trimoxazole, erythromycin, and chloramphenicol was determined using broth microdilution according to NCCLS methods. Urine sensitivity for antimicrobial activity was tested by pan susceptible Micrococcus luteus method. Forty two swabs were checked for “hidden clones” by selective plates containing penicillin or erythromycin compared to isolates found on gentamycin using antimicrobial susceptibility, serotype, and pulsed field gel electrophoresis (PFGE). Results Nasopharyngeal carriage of Sp among less than 5 years old children was 37.8% of the 502 subjects with upper respiratory infections. Beta lactam non susceptible strains remain uncommon (only 8%～9%) in this population. Resistance to erythromycin and co trimoxazole was very common (more than 70%). Only 33.9% of the isolates were those included in proposed pneumococcal conjugate vaccine formulations. Forty two samples containing Sp susceptible to both penicillin and erythromycin were tested for “hidden resistant clones” and 6 (14%) resistant clones were found. Conclusions Beta lactam resistance remains uncommon among the subjects studied in spite of widespread beta lactam use. However, it is necessary to monitor beta lactam resistance every year. Erythromycin and co trimoxazole resistance was very common. Erythromycin resistant strains were more common in children who recently took a macrolide. A small number of antibiotics resistant Sp strains were present in patients carrying susceptible Sp strains. Therefore, use of antimicrobial agents could lead to prominence of these resistant strains. Use of antibiotics might eradicate susceptible strains, but would leave the resistant strains alive in mucous membrane, which could be more dangerous for invasive disease. This study showed that the proposed conjugate vaccine serotypes did not cover majority of strains isolated; however, the distribution for invasive Sp strains may differ. Therefore, more studies should be done in this field in China.