title: Pneumococcal carriage in young children one year after introduction of the 13-valent conjugate vaccine in Italy.
abstract: BACKGROUND
  In mid 2010, the 7-valent pneumococcal conjugate vaccine (PCV7) was replaced by the 13-valent conjugate vaccine (PCV13) for childhood immunization in Italy. Our objective in this study was to obtain a snapshot of pneumococcal carriage frequency, colonizing serotypes, and antibiotic resistance in healthy children in two Italian cities one year after PCV13 was introduced.
  
  
  METHODS
  Nasopharyngeal swabs were obtained from 571 children aged 0-5 years from November 2011-April 2012. Pneumococcal isolates were serotyped and tested for antimicrobial susceptibility. Penicillin and/or erythromycin non-susceptible isolates were analyzed by Multi Locus Sequence Typing (MLST).
  
  
  RESULTS
  Among the children examined, 81.2% had received at least one dose of PCV7 or PCV13 and 74.9% had completed the recommended vaccination schedule for their age. Among the latter, 57.3% of children had received PCV7, 27.1% PCV13, and 15.6% a combination of the two vaccines. The overall carriage rate was 32.9%, with children aged 6-35 months the most prone to pneumococcal colonization (6-23 months OR: 3.75; 95% CI: 2.19-6.43 and 24-35 months OR: 3.15, 95%CI: 2.36-4.22). A total of 184 pneumococcal isolates were serotyped and divided into PCV7 (5.4%), PCV13 (18.0%), and non-PCV13 (82.0%) serotypes. Serotypes 6C, 24F, and 19A were the most prevalent (10.3%, 8.6%, and 8.1%, respectively). The proportion of penicillin non-susceptible (MIC >0.6 mg/L) isolates was 30.9%, while 42.3% were erythromycin resistant. Non-PCV13 serotypes accounted for 75.4% and 70.8% of the penicillin and erythromycin non-susceptible isolates, respectively.
  
  
  CONCLUSIONS
  Our results revealed low rates of PCV7 and PCV13 serotypes in Italian children, potentially due to the effects of vaccination. As the use of PCV13 continues, its potential impact on vaccine serotypes such as 19A and cross-reactive serotypes such as 6C will be assessed, with this study providing a baseline for further analysis of surveillance isolates.
authors.affiliation: Department of Infectious, Parasitic and Immune-Mediated Diseases, Istituto Superiore di Sanità, Rome, Italy.
authors.forename: Romina
authors.initials: R
authors.lastname: Camilli
authors.forename: Laura
authors.initials: L
authors.lastname: Daprai
authors.forename: Francesca
authors.initials: F
authors.lastname: Cavrini
authors.forename: Donatella
authors.initials: D
authors.lastname: Lombardo
authors.forename: Fabio
authors.initials: F
authors.lastname: D'Ambrosio
authors.forename: Maria
authors.initials: M
authors.lastname: Del Grosso
authors.forename: Maria Fenicia
authors.initials: MF
authors.lastname: Vescio
authors.forename: Maria Paola
authors.initials: MP
authors.lastname: Landini
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Pascucci
authors.forename: Erminio
authors.initials: E
authors.lastname: Torresani
authors.forename: Maria Laura
authors.initials: ML
authors.lastname: Garlaschi
authors.forename: Vittorio
authors.initials: V
authors.lastname: Sambri
authors.forename: Annalisa
authors.initials: A
authors.lastname: Pantosti
mesh_terms: D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D011008:Pneumococcal Infections / Q000276:immunology* / Q000517:prevention & control; D022242:Pneumococcal Vaccines / Q000627:therapeutic use*; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000276:immunology*; D018074:Vaccines, Conjugate / Q000627:therapeutic use*
chemical_list: D022242:Pneumococcal Vaccines; D018074:Vaccines, Conjugate