Non-susceptibility trends and serotype coverage by conjugate pneumococcal vaccines in a Tunisian paediatric population: a 10-year study.

Streptococcus pneumoniae is one of the major causative agents of invasive infectious disease in children <5 years old globally. The aim of this study was to analyze the antimicrobial resistance and the serotype distribution of S. pneumoniae isolates from the paediatric population in Tunisia and to specify the serotypes coverage by the conjugate pneumococcal vaccines. Antimicrobial susceptibility was determined by the disk diffusion method. Minimal inhibitory concentrations of beta-lactams were determined using the E test method (AB BIODISK). Serotypes were determined by agglutination of latex particles, which identified a subset of serotypes included in pneumococcal conjugate vaccines (1, 3, 4, 5, 14) and some of the serogroups. This was followed by the Neufeld test using monovalent antisera (Statens Serum Institute) specific for the other serotypes included in pneumococcal conjugate vaccines 7, 10 and 13 (PCV7, PCV10, PCV13): 6A, 6B, 7F, 9V, 18C, 19A, 19F and 23F. During the study period, 200 invasive and 310 non-invasive pneumococcal isolates were obtained from paediatric patients ranging in age from newborn to 16 years. Among these 510 isolates, 53.4% had reduced susceptibility to penicillin. Penicillin resistance was higher among S. pneumoniae isolates recovered from samples associated with non-invasive vs. invasive disease (60.6% vs. 45%). All the strains were susceptible to pristinamycin, vancomycin, teicoplanin and fosfomycin. Serotype 14 was the most frequently isolated serotype (22.2%), followed by serotypes 19F (15.5%) and 23F (10.3%). Of all strains typed, the percentage of serotypes covered by PCV7, PCV10 and PCV13 were 66.4%, 73% and 78%, respectively (76.1% for invasive pneumococcal isolates, 79.8% for non invasive pneumococcal isolates for PVC13). Continual surveillance of antibiotic susceptibility and careful use of antibiotics are recommended. The introduction of the new conjugate vaccine should be greatly beneficial for reducing pneumococcal invasive diseases among Tunisian children.