51 Epidemiology, Serotypes Distribution and Antibiotic Susceptibility of Streptococcus Pneumoniae Strains Associated with Invasive Pneumococcal Diseases in a Pediatric Tertiary Care Center in Montreal

Streptococcus pneumoniae (Sp) is a leading cause of invasive bacterial infections. Worldwide, a decreased susceptibility to antibiotics has been reported. The recently available heptavalent conjugated pneumococcal vaccine (PCV-7) includes serotypes responsible for the majority of Invasive Pneumococcal Diseases (IPD) and significant numbers of isolates being resistant to antibiotics.

The aim of this study was to review the epidemiology, serotype distribution and antibiotic susceptibility pattern of Sp strains isolated from children seen at Sainte-Justine Hospital with IPD.

We reviewed the microbiological characteristics of Sp strains isolated from children with IPD from September 2001 to September 2003. Serotyping was performed at the National Center for Streptococcus in Alberta and antimicrobial susceptibility testing was done in our microbiology laboratory. Most of the susceptibility results were confirmed at the Quebec Public Health Laboratory.

Sp was recovered from 124 samples over the two-year study period but data were available for 104 of them: 92 blood cultures, 9 cere-brospinal fluids, 2 joint and 1 peritoneal fluids. The patient mean age was 35 months (median: 17 months, range: 4 months-17 years). Children less than 2 years of age represented 52.6% (62/104) of all cases. According to serotyping results, 80.6% (50/62) of the strains were included into the PCV-7. Of all strains isolated from children above 2 years, 78.6% (33/42) were included into the PCV-7 and 90.5 % into the polysaccharide vaccine. Decreased susceptibility to penicillin was found in 20.2% of all tested strains (7.7% highly resistant – MIC ≥2 mg/L) and 81.4 % of them were included into the PCV-7. Macrolide resistance was found in 37.5% of all tested strains. Combined resistance to both penicillin and macrolides was found in 16.35% of all tested strains.

As already reported and shown is this retrospective study, Sp is responsible for invasive diseases in young children. However, almost half of the IPD diagnosed at Sainte-Justine hospital occurred in children above 2 years of age and are therefore largely preventable. Antimicrobial resistance of Sp concerns not only penicillin but also and more significantly the macrolides. Moreover, most of the penicillin resistant strains were included into the PCV-7. Prevention strategies based on both conjugated and polysaccharide vaccines would be useful to limit IPD and act on pneumococcal resistance.