In Morocco, 13-valent pneumococcal conjugated vaccine (PCV) was introduced in the childhood immunization program in October 2010 and changed to PCV-10 in July 2012. The purpose of this study was firstly to determine the prevalence of pneumococcus carriage in a population of febrile infants in Marrakesh and secondly, to investigate the risk factors for carriage and the distribution of circulating serotypes.

This prospective study was conducted from February to June 2017, in the pediatric emergency department of the Mother and Child Hospital of Mohammed VI University Hospital Centre (UHC) in Marrakesh. At total of 183febrile infants, aged 2–18months, were enrolled in this study and were swabbed for nasopharyngeal carriage. Pneumococci were cultured, identified, serotyped, and tested for penicillin susceptibility. Demographic data and risk factors for carriage were collected. The statistical analyses performed were the following: the analysis of the risk factors using logistic regression, the estimation of serotype diversity with the Simpson index, and the Chi² test to compare serotype distribution in the prevaccination (a cohort of 660 healthy children, less than 2years old, in the Marrakesh region, in 2008–2009) and postvaccination periods.

The prevalence of Streptococcus pneumoniae carriage was 68.3%. Of the 183infants enrolled in this study, 111 had received at least one dose of PCV-10. Colonization by vaccine serotype among febrile children was related to incomplete vaccination status. In total, vaccine serotypes accounted for 6.4% (n=8): 19F (n=2), 1 (n=2) and one strain for each of the following serotypes: 14, 23F, 6B, and 9V. Non-vaccine and nontypeable strains presented 63.2% and 23.2%, respectively, with dominance of serotypes 6A (6.4%), 15A/15F (5.6%), 20, 22F/22A, 23B, and 11A/11D with a prevalence of 3.2%. The rate of pneumococcus strains with reduced susceptibility to penicillin was 33.6%, of which 90.2% were non-vaccine serotypes and nontypeable strains. Serotype diversity increased in the postvaccination period and the effectiveness of PCV-10 against vaccine serotypes was estimated at 89.6%.

An important change in the distribution of vaccine and non-vaccine serotypes was observed after the introduction of the PCVs. In fact, the prevalence of vaccine serotypes decreased significantly while non-vaccine serotypes emerged. These results underscore the importance of maintaining close and prolonged surveillance of serotype distribution to monitor the dynamics of nasopharyngeal pneumococcal carriage.