Analysis of invasive pneumonia-causing strains of Streptococcus pneumoniae: serotypes and antimicrobial susceptibility

Objectives: To identify the most common pneumococcal serotypes in children hospitalized with invasive pneumonia, correlate isolated serotypes with those included in conjugate vaccines, and ascertain the sensitivity of the isolated pneumococcal strains to penicillin and other antibiotics. Methods: From January 2003 to October 2008, a retrospective study of hospitalized children with a diagnosis of Streptococcus pneumoniae pneumonia was conducted at the university hospital of Universidade de Sao Paulo. Criteria for inclusion were: age greater than 29 days and less than 15 years, radiological and clinical diagnosis of pneumonia, and isolation of Streptococcus pneumoniae in blood cultures and/or pleural effusion. Results: The study included 107 children. The most common serotypes were 14 (36.5%), 1 (16%), 5 (14.6%), 6B (6.3%) and 3 (4.2%). The proportion of identified serotypes contained in the heptavalent, 10-valent and 13-valent conjugate vaccines was 53.1, 86.5, and 96.9%, respectively. Pneumococcal strains were sensitive to penicillin (minimum inhibitory concentration, MIC <= 2 mu g/mL) in 100 cases (93.5%) and displayed intermediate resistance (MIC = 4 mu g/mL) in 7 cases (6.5%). No strains were penicillin-resistant (MIC >= 8 mu g/mL) according to the Clinical and Laboratory Standards Institute 2008 standards. Tested isolates were highly sensitive to vancomycin, rifampicin, ceftriaxone, clindamycin, erythromycin, and chloramphenicol. Conclusions: Our results confirm a significant potential impact of conjugate vaccines, mainly 10-valent and 13-valent, on invasive pneumonia. Furthermore, susceptibility testing results show that penicillin is still the treatment of choice for invasive pneumonia in our setting.