title: Dynamics of pneumococcal carriage among day-care center attendees during the transition from the 7-valent to the higher-valent pneumococcal conjugate vaccines in Greece.
abstract: BACKGROUND
  In Greece recently, higher-valent pneumococcal conjugate vaccines (PCVs) replaced the 7-valent (PCV7); the 10-valent (PCV10) became available in May 2009 and the 13-valent (PCV13) in June 2010.
  
  
  METHODS
  We investigated the nasopharyngeal colonization with Streptococcus pneumoniae in day-care center attendees in Athens and the prefecture of Viotia. Between December 2010 and June 2011, nasopharyngeal cultures were obtained 4 times, at enrollment and then every 6 to 8 weeks.
  
  
  RESULTS
  Among the 233 children, 225 (96.6%) had been vaccinated with ≥1 dose of PCV7. One tenth of the PCV7 vaccinated attendees had also received ≥1 dose of PCV13 or PCV10. During the 4 samplings, 358 isolates were recovered from a total of 874 samples. Of the 233 children, 183 (78.5%) were found to carry S. pneumoniae at least once. The overall serotype distribution among carriers was similar regardless of the time lapsed since the last PCV7 dose. A high frequency of 19A (17.1%) coincided with a low frequency of 19F (1.4%). Non-PCV13 serotypes accounted for 73.1% of the isolates; 23B, 15B/C, 16F, 21, 11A, 15A, 6C, 10A, 22F and 23A were the most common. Among attendees aged 24-59 months (median age 42 months), prolonged carriage of a non-PCV13 serotype was relatively common, mainly for 21 and 16F. One out of 4 cases of colonization with the prevalent non-PCV13 serotypes was followed by persistent carriage for 5 to 14 weeks.
  
  
  CONCLUSIONS
  During this period of transition to the higher-valent PCVs in the day-care center setting, non-PCV13 serotypes dominated and exhibited prolonged colonization. The frequency and the duration of prolonged carriage tends to be increased, if sampling frequency increases and the carriage time before and after positive cultures is taken into consideration. Further studies regarding the fitness of the colonizing non-PCV13 serotypes will likely to be seen in the future.
authors.affiliation: Department of Pediatrics, University of Thessaly, School of Health Sciences, Faculty of Medicine, General University Hospital, Larissa, Greece.
authors.forename: Ioanna N
authors.initials: IN
authors.lastname: Grivea
authors.affiliation: Children's Respiratory Unit, Faculty of Medicine, University of Athens, Attikon General University Hospital, Athens, Greece.
authors.forename: Kostas N
authors.initials: KN
authors.lastname: Priftis
authors.affiliation: Children's Respiratory Unit, Faculty of Medicine, University of Athens, Attikon General University Hospital, Athens, Greece.
authors.forename: Apostolos
authors.initials: A
authors.lastname: Giotas
authors.affiliation: Children's Respiratory Unit, Faculty of Medicine, University of Athens, Attikon General University Hospital, Athens, Greece.
authors.forename: Doxa
authors.initials: D
authors.lastname: Kotzia
authors.affiliation: Department of Pediatrics, University of Thessaly, School of Health Sciences, Faculty of Medicine, General University Hospital, Larissa, Greece.
authors.forename: Alexandra G
authors.initials: AG
authors.lastname: Tsantouli
authors.affiliation: Children's Respiratory Unit, Faculty of Medicine, University of Athens, Attikon General University Hospital, Athens, Greece.
authors.forename: Konstantinos
authors.initials: K
authors.lastname: Douros
authors.affiliation: Department of Pediatrics, University of Thessaly, School of Health Sciences, Faculty of Medicine, General University Hospital, Larissa, Greece.
authors.forename: Aspasia N
authors.initials: AN
authors.lastname: Michoula
authors.affiliation: Department of Pediatrics, University of Thessaly, School of Health Sciences, Faculty of Medicine, General University Hospital, Larissa, Greece. Electronic address: syrogian@otenet.gr.
authors.forename: George A
authors.initials: GA
authors.lastname: Syrogiannopoulos
mesh_terms: D002353:Carrier State / Q000453:epidemiology*; D002656:Child Day Care Centers / Q000706:statistics & numerical data*; D002675:Child, Preschool; D003430:Cross-Sectional Studies; D062665:Epidemiological Monitoring; D005260:Female; D006115:Greece / Q000453:epidemiology; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D006801:Humans; D007223:Infant; D008137:Longitudinal Studies; D008297:Male; D009305:Nasopharynx / Q000382:microbiology; D011008:Pneumococcal Infections / Q000453:epidemiology / Q000517:prevention & control; D022242:Pneumococcal Vaccines / Q000008:administration & dosage*; D015995:Prevalence; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification; D018074:Vaccines, Conjugate / Q000008:administration & dosage
chemical_list: C538862:13-valent pneumococcal vaccine; D000069443:Heptavalent Pneumococcal Conjugate Vaccine; D022242:Pneumococcal Vaccines; D018074:Vaccines, Conjugate
keywords: 10-Valent pneumococcal conjugate vaccine; 13-Valent pneumococcal conjugate vaccine; 7-Valent pneumococcal conjugate vaccine; Day-care centers; Nasopharyngeal carriage; Streptococcus pneumoniae