Streptococcus pneumoniae carriage among healthy and sick paediatric patients before the generalized implementation of the 13-valent pneumococcal vaccine in Morocco, 2010–2011

Introduction Nasopharyngeal carriage studies provide insights into the local prevalence of circulating pneumococcal serotypes. These data are critical to vaccination monitoring, as they allow for the prediction and assessment of impact. Very little data are available on the carriage of pneumococcal serotypes in Morocco. The aim of the study was to describe the prevalence of Streptococcus pneumoniae carriage and serotype distribution among healthy and sick pediatric patients with ages ranging from 2 to 59 months. Methods Were included, patients admitted for severe clinical pneumonia according to WHO definition during a one-year survey from November 2010 to December 2011 and healthy children visiting primary health care centers for routine vaccination in the province of Rabat. These sites were selected randomly and the sample size for the community study ( n  = 200) was calculated based on the preliminary estimation of carriage rates. Nasopharyngeal samples were obtained from consent children using a mini culturette extra-thin flexible wire swab. Nasal samples were cultured using conventional methods Molecular. Capsular typing of pneumococcal strains was performed using sequential multiplex real-time PCR targeting 24 common serotypes (1, 3, 4, 5, 6A, 6B, 7F/A, 8, 9 V/A/N/l, 14, 15B/C, 18 C/B, 19A, 19F/B/C, 23A and 23F) [8]. Data analysis Study variables were analyzed and summarized in frequency tables. Quantitative variables are expressed as the means with their corresponding standard deviations. Qualitative variables are presented as percentages with 95% confidence intervals. Results The proportion of infants less than one year of age was 30.6% (214/700) for the admitted patients and 70.7% (138/195) for the children from the community. Carriage rates were 40.5% (79/195) for healthy children and 22.8% (159/697) for sick children. Vaccine coverage for the circulating serotypes was 55.9% (66/118) among hospitalized children and 52.1% (24/46) for healthy children. Among admitted patients, the monthly distribution of carriage was significantly different ( P P  = 0.003). Carriage rates also varied, albeit not significantly, according to the number of pneumococcal vaccine doses received. The most commonly observed circulating serotypes included 6A, 6B and 19F, all of which are included in the current 13-valent anti-pneumococcal conjugate vaccine that was recently introduced in Morocco. The proportion of the carriage among healthy children was two to eight times higher than in children less than 12 months of age, while the distribution of 19F/B/C was two-fold higher among children who had received at least one dose of the 13-valent pneumococcal conjugate vaccine. Conclusion Monitoring of circulating serotypes remains necessary after vaccine introduction to assess whether serotype replacement is occurring.