Nasopharyngeal carriage, serotype distribution and antimicrobial resistance of Streptococcus pneumoniae among children from Brazil before the introduction of the 10-valent conjugate vaccine

Abstract

Background: Streptococcus pneumoniae remains a major cause of childhood morbidity and mortality worldwide. Nasopharyngeal colonization plays an important role in the development and transmission of pneumococcal diseases, and infants and young children are considered to be the main reservoir of this pathogen. The aim of this study was to evaluate the rates and characteristics associated with nasopharyngeal carriage, the distribution of serotypes and the antimicrobial resistance profiles of Streptococcus pneumoniae among children in a large metropolitan area in Brazil before the introduction of the 10-valent pneumococcal conjugate vaccine.

Methods: Between March and June 2010, nasopharyngeal swabs were collected from 242 children aged <6 years attending one day care center and the emergency room of a pediatric hospital. Pneumococcal isolates were identified by conventional methods and serotypes were determined by a sequential multiplex PCR assay and/or the Quellung reaction. The antimicrobial susceptibilities of the pneumococci were assessed by the disk diffusion method. MICs for erythromycin and penicillin were also performed. Erythromycin resistance genes were investigated by PCR.

Results: The overall colonization rate was 49.2% and it was considerably higher among children in the day care center. Pneumococcal carriage was more common among day care attenders and cohabitants with young siblings. The most prevalent serotypes were 6B, 19F, 6A, 14, 15C and 23F, which accounted for 61.2% of the isolates. All isolates were susceptible to clindamycin, levofloxacin, rifampicin and vancomycin. The highest rate of non-susceptibility was observed for sulphamethoxazole-trimethoprim (51.2%). Penicillin non-susceptible pneumococci (PNSP) accounted for 27.3% of the isolates (MICs of 0.12-4 μg/ml). Penicillin non-susceptibility was strongly associated with serotypes 14 and 23F. Hospital attendance and the presence of respiratory or general symptoms were frequently associated with PNSP carriage. The two erythromycin-resistant isolates (MICs of 2 and 4 μg/ml) belonged to serotype 6A, presented the M phenotype and harbored the mef(A/E) gene.

Conclusions: Correlations between serotypes, settings and penicillin non-susceptibility were observed. Serotypes coverage projected for the 10-valent pneumococcal conjugate vaccine was low (45.5%), but pointed out the potential reduction of PNSP nasopharyngeal colonization by nearly 20%.

Figure 1

Distribution of penicillin non-susceptible (MIC > 0.6 μg/ml) Streptococcus pneumoniae considering the different MIC breakpoints. Pen, penicillin; R, resistant; I, intermediate. MIC, Minimum Inhibitory Concentrations. Adopted MIC breakpoints: oral penicillin V (I = 0.12-1.0 μg/ml; R ≥ 2.0 μg/ml); penicillin parenteral (nonmeningitis - I = 4.0 μg/ml; R ≥ 8.0 μg/ml); and penicillin parenteral (meningitis - R ≥ 0.12 μg/ml).