title: Unaltered pneumococcal carriage prevalence due to expansion of non-vaccine types of low invasive potential 8years after vaccine introduction in Stockholm, Sweden.
abstract: To evaluate the carriage prevalence, serotype distribution, and antibiotic resistance for pneumococcal carriage isolates collected 4-8years after introduction of pneumococcal conjugate vaccines (PCVs) in Stockholm, Sweden, and to identify risk factors for carriage and calculate the invasive disease potential for emerging serotypes.
  
  
  
  Nasopharyngeal aspirates were collected from 3024 children aged 0-<5years at regular visits at 23 Child Health Centers in Stockholm County in 2011-2015, and from 787 parents in 2014-2015. The invasive disease potential was calculated for serotypes using invasive disease isolates from 824 patients of all ages identified in the Stockholm County during the same time period as the carriage isolates.
  
  
  
  A total carriage prevalence of 30% did not change during the study period. Non-vaccine types (NVT) dominated (94% by 2015) and the most common serotypes in descending order were 11A, 23B, 35F and 21. Risk factors for carriage were: age ⩾3months-<3years, having siblings, attending day-care and having travelled abroad the last 3months. Antibiotic resistance remained low. The invasive disease potential was high for NVT 8, 9N, 12F, and 22F, while low for a majority of emerging NVTs in carriage.
  
  
  
  The carriage prevalence remained the same 4-8years after vaccine introduction, but serotype replacement became almost complete. A majority of emerging NVTs in carriage showed a low invasive disease potential. Carriage studies are an important complement to invasive disease surveillance to understand the full effect of PCV vaccine programs.
authors.affiliation: The Public Health Agency Sweden, SE-171 82, Solna, Sweden; Department of Public Health Sciences, Karolinska Institutet, SE-171 77 Stockholm, Sweden. Electronic address: ann.lindstrand@folkhalsomyndigheten.se.
authors.forename: Ann
authors.initials: A
authors.lastname: Lindstrand
authors.affiliation: The Public Health Agency Sweden, SE-171 82, Solna, Sweden.
authors.forename: Ilias
authors.initials: I
authors.lastname: Galanis
authors.affiliation: The Public Health Agency Sweden, SE-171 82, Solna, Sweden.
authors.forename: Jessica
authors.initials: J
authors.lastname: Darenberg
authors.affiliation: The Public Health Agency Sweden, SE-171 82, Solna, Sweden.
authors.forename: Eva
authors.initials: E
authors.lastname: Morfeldt
authors.affiliation: Department of Medicine, Unit of Infectious Diseases, Karolinska University Hospital, SE-171 76, Solna, Sweden.
authors.forename: Pontus
authors.initials: P
authors.lastname: Naucler
authors.affiliation: Sachs' Children and Youth Hospital, South General Hospital, SE-118 83 Stockholm, Sweden; Department of Clinical Sciences and Education, Karolinska Institutet, SE-171 77 Stockholm, Sweden.
authors.forename: Margareta
authors.initials: M
authors.lastname: Blennow
authors.affiliation: Department of Public Health Sciences, Karolinska Institutet, SE-171 77 Stockholm, Sweden; Sachs' Children and Youth Hospital, South General Hospital, SE-118 83 Stockholm, Sweden.
authors.forename: Tobias
authors.initials: T
authors.lastname: Alfvén
authors.affiliation: The Public Health Agency Sweden, SE-171 82, Solna, Sweden; Department of Microbiology, Tumor and Cell Biology, Karolinska Institutet, SE-171 77 Stockholm, Sweden; Department of Clinical Microbiology, Karolinska University Hospital, SE-171 76 Stockholm, Sweden.
authors.forename: Birgitta
authors.initials: B
authors.lastname: Henriques-Normark
authors.affiliation: Department of Medicine, Unit of Infectious Diseases, Karolinska University Hospital, SE-171 76, Solna, Sweden; Department of Communicable Disease Control and Prevention, SE-118 83, Stockholm County Council, Sweden.
authors.forename: Åke
authors.initials: Å
authors.lastname: Örtqvist
mesh_terms: D002353:Carrier State / Q000453:epidemiology* / Q000382:microbiology; D002656:Child Day Care Centers; D002675:Child, Preschool; D024881:Drug Resistance, Bacterial; D005260:Female; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D008297:Male; D009305:Nasopharynx / Q000382:microbiology; D010290:Parents; D011008:Pneumococcal Infections / Q000453:epidemiology* / Q000517:prevention & control; D022242:Pneumococcal Vaccines / Q000627:therapeutic use*; D015995:Prevalence; D011446:Prospective Studies; D012307:Risk Factors; D012703:Serotyping; D013296:Streptococcus pneumoniae / Q000145:classification; D013548:Sweden / Q000453:epidemiology; D018074:Vaccines, Conjugate / Q000627:therapeutic use
chemical_list: D022242:Pneumococcal Vaccines; D018074:Vaccines, Conjugate
keywords: Colonization; Nasopharyngeal pneumococcal carriage; Pneumococcal conjugate vaccine; Pneumococcal serotype