Pneumococcal colonization in healthy children and pediatric patients with chronic underlying disease

Background: Prevalence of pharyngeal Streptococcus pneumoniae (Sp) serotype carriage in school-children and adolescents can predict the potential impact of Sp conjugate vaccines and could suggest the duration of the conferred capsular-specific immunity. Aim of this study was to evaluate 13-valent pneumococcal conjugate vaccine (PCV13) serotypes carriage by Italian children and adolescents. Methods: Oropharyngeal swabs were obtained in classrooms and outpatient clinics from subjects attending primary (6-9 years), secondary (10-14 years) and high school (≥15 years). General characteristics and vaccination status of the enrolled children were recorded. Standardized methods were used to extract bacterial genomic DNA and to test it for lytA and wzg (cpsA) genes of Sp. Positive cases were serotyped using primers and probes for the identification of PCV13 serotypes. Results: A total of 1,230 healthy children and 1,230 age- and sex-matched patients with chronic underlying disease (443 severe asthma, 213 cystic fibrosis, 277 oncohematological diseases treated with aggressive or maintenance chemotherapy and 297 type 1 diabetes) were evaluated. Of these, 740 (30.0%) children were fully vaccinated with 7-valent PCV (PCV7) and none was vaccinated with PCV13. The incidence of Sp carriage was age-related (25.8-74.9% in those aged 6-9 years, 14.7-51.8% in those 10-14 years and 7.2-32.7% in those ≥15 years, respectively; p<0.001) and appeared independent on the vaccination status. In all the age groups, children with type 1 diabetes or severe asthma were those with significantly higher colonization rates in comparison with the other patients (p<0.05). Overall, 713 (57.9%) healthy children showed pneumococcal colonization. Serotypes 19F, 9V and 14 were more common among PCV7-vaccinated than among PCV7-not vaccinated subjects (p<0.05). Conclusions: The high prevalence of carriers in all of the age groups independently from previous pneumococcal vaccination and only partially related to underlying disease seems to indicate that the extensive use of PCVs in older children and adolescents might be useful to persistently reduce pharyngeal colonisation of these subjects.