title: Dynamics of pneumococcal nasopharyngeal carriage in healthy children attending a day care center in northern Spain. Influence of detection techniques on the results.
abstract: BACKGROUND
  Pneumococcal nasopharyngeal carriage precedes invasive infection and is the source for dissemination of the disease. Differences in sampling methodology, isolation or identification techniques, as well as the period (pre -or post-vaccination) when the study was performed, can influence the reported rates of colonization and the distribution of serotypes carried.
  
  
  OBJECTIVE
  To evaluate the prevalence and dynamics of pneumococcal nasopharyngeal colonization in healthy children aged 6-34 months attending a day care center with a high level of hygiene and no overcrowding. The study was performed 3-4 years after the 7-valent pneumococcal vaccine was introduced, using multiple methodologies to detect and characterize the isolates.
  
  
  METHODS
  Over 12 months, 25 children were sampled three times, 53 children twice and 27 children once. Three Streptococcus pneumoniae typing techniques were used: Quellung, Pneumotest-Latex-kit and multiplex-polymerase chain reaction (PCR). The similarity of isolates of the same serotype was established by pulsed field gel electrophoresis (PFGE) and occasionally the multilocus sequence type (ST) was also determined.
  
  
  RESULTS
  Overall pneumococcal carriage and multiple colonization rates were 89.5% (94/105) and 39%, respectively. Among 218 pneumococci detected, 21 different serotypes and 13 non-typeable isolates were found. The most prevalent serotypes were 19A, 16F and 15B. Serotypes 15B, 19A and 21 were mainly found as single carriage; in contrast serotypes 6B, 11A and 20, as well as infrequent serotypes, were isolated mainly as part of multiple carriage. Most 19A isolates were ST193 but most serotypes showed high genetic heterogeneity. Changes in the pneumococci colonizing each child were frequent and the same serotype detected on two occasions frequently showed a different genotype. By multiplex-PCR, 100% of pneumococci could be detected and 94% could be serotyped versus 80.3% by the Quellung reaction and Pneumotest-Latex in combination (p < 0.001).
  
  
  CONCLUSIONS
  Rates of S. pneumoniae carriage and multiple colonization were very high. Prevalent serotypes differed from those found in similar studies in the pre-vaccination period. In the same child, clearance of a pneumococcal strain and acquisition of a new one was frequent in a short period of time. The most effective technique for detecting pneumococcal nasopharyngeal carriers was multiplex-PCR.
authors.affiliation: Microbiology Department, Hospital Universitario Donostia-Instituto Biodonostia, San Sebastián, Spain.
authors.forename: María
authors.initials: M
authors.lastname: Ercibengoa
authors.forename: Nerea
authors.initials: N
authors.lastname: Arostegi
authors.forename: José M
authors.initials: JM
authors.lastname: Marimón
authors.forename: Marta
authors.initials: M
authors.lastname: Alonso
authors.forename: Emilio
authors.initials: E
authors.lastname: Pérez-Trallero
mesh_terms: D015373:Bacterial Typing Techniques; D002353:Carrier State / Q000382:microbiology*; D002656:Child Day Care Centers / Q000706:statistics & numerical data*; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007223:Infant; D008297:Male; D009305:Nasopharynx / Q000382:microbiology*; D011008:Pneumococcal Infections / Q000453:epidemiology / Q000382:microbiology*; D016133:Polymerase Chain Reaction / Q000379:methods*; D013030:Spain / Q000453:epidemiology; D013296:Streptococcus pneumoniae / Q000145:classification / Q000235:genetics / Q000302:isolation & purification*