Antimicrobial susceptibility of Streptococcus pneumoniae in pediatric and adult population from Santiago, 1997-2003

Background: In Chile, the emergence of drug-resistant strains of Streptococcus pneumoniae has complicated treatment decisions and may lead to treatment failures. Aim: to examine antimicrobial resistance trends among pneumococcal isolates from the Catholic University Hospital between 1997 and 2003. Material and methods: During a seven-year period, we examined 901 strains of S. pneumoniae isolated from sterile and non-sterile samples from adult and pediatric population. Results: Overall, 20% of isolates showed intermediate resistance to penicillin (MIC: 0.12-1 µg/ml) y 10.8% high level of resistance to penicillin (MIC ³ 2 µg/ml). Pneumococcal resistance to penicillin did not change significantly during the study period, but it was more common in pediatric patients and isolates from non-sterile samples. No isolate had a MIC ³ 8 µg/ml for penicillin. Twenty one percent of pneumococcal strains were resistant to erythromycin, 41.6% to trimethoprim-sulfamethoxazole and 3.6% to chloramphenicol. Macrolides resistance tended to increase between 1997 and 2003. Fourteen percent of strains showed intermediate resistance (MIC: 1 µg/ml) and 2.5%, a high level of resistance to cefotaxime (MIC: ³ 2 µg/ml). No isolate had a CIM ³ 4 µg/ml for cefotaxime. Among those isolates with intermediate or high level of resistance to penicillin, there were significantly more isolates highly resistant to erythromycin, trimethoprim-sulfamethoxazole and cefotaxime. Conclusions: Multidrug-resistant pneumococci are common and are increasing in our country, particularly in pediatric population, probably associated to indiscriminate ambulatory prescription of antimicrobials (Rev Méd Chile 2005; 133: 42-49)