Pneumococcal serotype distribution in 1315 nasopharyngeal swabs from a highly vaccinated cohort of Italian children as detected by RT-PCR

Angela Pasinato, Giuseppe Indolfi, Paola Marchisio, Claudia Valleriani, Martina Cortimiglia, Valter Spanevello, Giampietro Chiamenti, Roberto Buzzetti, Massimo Resti, Chiara Azzari

Research output: Contribution to journalArticlepeer-review


The long term impact of 7-valent pneumococcal conjugate vaccine (PCV7) on pneumococcal colonization patterns remains unclear. Carriage and distribution of Streptococcus pneumoniae serotypes as detected by RT-PCR were evaluated in a cohort of 1315 children. S. pneumoniae was identified in the nasopharyngeal swab of 734 children (55.8%); 488/734 (66.5%) children carried more than 1 pneumococcal serotype. As a consequence of co-colonization, a total of 1,728 S. pneumoniae (belonging to 33 serotypes) were identified. As immunogenicity between 2 and 3 doses of PCV7 in the first year of life has been demonstrated to be similar, serotypes distribution was evaluated categorizing vaccination status as 0,1 and 2 or more doses in the first year of life. Among children who started vaccination in the first year of life, PCV7 serotypes were carried in 296 of 1,123 (29.5%) children who had received ≥2 PCV7 doses while were carried in 26 of 108 (26.8%) who had received no doses (p=not significant); only 17 children received 1 PCV7 and 3 of them were found positive for PCV7 serotypes. Among those who had received ≥2 doses of PCV7 in the first year of life, 47 of 192 (19.7%) carried a PCV7 serotype during the first year after last vaccination, 50 of 125 (28.6%) during the second year, 79 of 224 (35.3%) during the third year, and 65 of 143 (45.5%) during the fourth year (p 0.0001). We did not identify risk factors for PCV7 carriage among children that had received >2 vaccine doses. This study suggests that S. pneumoniae is present in the nasopharynx of the majority of children 0-5 years even if vaccinated, that PCV7 serotypes can be found in nasopharyngeal swabs of PCV7 vaccinated children and that the frequency of PCV7 serotypes increases with the increase of interval from vaccination.

Original languageEnglish
Pages (from-to)1375-1381
Number of pages7
Issue number12
Publication statusPublished - Mar 10 2014


  • 7-valent pneumococcal conjugate vaccine
  • Nasopharyngeal carriage
  • Real time-polymerase chain reaction
  • Serotypes
  • Streptococcus pneumoniae

ASJC Scopus subject areas

  • Immunology and Microbiology(all)
  • Infectious Diseases
  • Public Health, Environmental and Occupational Health
  • veterinary(all)
  • Molecular Medicine


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