Changing epidemiology of pediatric Streptococcus pneumoniae isolates before vaccine introduction in Casablanca...

The objective of this study was to describe the evolution over time of serotypes and antimicrobial resistance of Streptococcus pneumoniae isolates responsible for invasive pneumococcal disease (IPD) in children ≤5 years in Casablanca (Morocco), before vaccine introduction. Isolates recovered from cases of IPD in children ≤5 years during two study periods (1994-2001 and 2006-2010) were compared in terms of serotypes and antimicrobial susceptibility. Serogrouping was done using Pneumotest Kit and serotyping was done by the Quellung capsular swelling. Antibiotic susceptibility pattern was determined by Etest method. The theoretical coverages of the 7-, 10- and 13-valent pneumococcal vaccines were determined. A total of 85 and 102 isolates were studied for the two periods, respectively. During the first period, the most prevalent serogroups/serotypes were 5, 7, 1, 14, 6, 23, 19, 2, 15 and 18, whereas during the second study period, the most frequent were 19, 14, 6, 23, 5, 1 and 18. From 2006 to 2010, serotype 19A accounted for 7.8% of the isolates, whereas serogroups 33 and 22 were rarely isolated (1% each). Assuming cross protection among serogroups, the respective coverage rates for the first vs. second periods reached 40% vs. 53.9% for PCV7, 74.1% vs. 71.6% for PCV10 and 75.3% vs. 82.4% for PCV13. The prevalence of penicillin-nonsusceptibility increased (22.4% vs. 48.5%) as well as the levels of penicillin-resistance (5.9% vs. 15.8%). Penicillin-nonsusceptibility was relatively low across both study periods in serogroups 7, 15, 1 and 5, whereas it was high in serogroups 14, 19 and 23. In conclusion, serotype fluctuations and increases in antibiotic resistance of S. pneumoniae occurred in Casablanca before vaccine introduction. Both of these variations are probably linked to the increase in antibiotic use that has occurred in Casablanca over time. There is a need for a continuous surveillance to assess the vaccine formulations, monitor vaccine impact and to guide treatment recommendations.