title: Probability of vertical transmission ofChlamydia trachomatisestimated from national registry data.
abstract: Chlamydia trachomatiscolonisation is common in pregnant women, and it has been claimed that mother-to-child transmission may occur in 10%-70% of deliveries.C. trachomatisinfections are nevertheless rarely encountered in infants in clinical practice. In order to evaluate the reason for this discrepancy, we designed a nationwide study of theC. trachomatisvertical transmission.
  
  
  
  Children with a possibleC. trachomatisinfection were identified from two national health registries in 1996-2011. Copies of the children's medical records were reviewed and maternal serum bank samples obtained during the index pregnancies were analysed forC. trachomatisantibodies. The risk of vertical transmission was calculated using data from two earlier studies in which nucleic acid amplification test (NAAT) positivity and seroconversion rates among women in the general population were reported.
  
  
  
  Altogether 206 children had a possibleC. trachomatisinfection, which represents 0.22 per 1000 live births (95% CI 0.19 to 0.25). The risk of vertical transmission among the estimated 24 901 NAAT-positive mothers was 0.8% (95% CI 0.7 to 0.9). Based on the annual seroconversion rate of maternal antitrachomatis antibodies, the risk of vertical transmission was 1.8% (95% CI 1.5 to 2.0). Altogether 35% of the maternal serum samples obtained in the first trimester of a pregnancy leading to aC. trachomatisinfection in the infant were negative, implying that the infection was acquired during pregnancy.
  
  
  
  C. trachomatisinfections in infants were rare, with a population-based occurrence of 0.22 per 1000 live births. The risk of vertical transmission ofC. trachomatisin the population was <2%, which is significantly lower than reported earlier.
authors.affiliation: Department of Children and Adolescents, Oulu University Hospital, Oulu, Finland.|PEDEGO Research Unit and Medical Research Center Oulu, University of Oulu, Oulu, Finland.
authors.forename: Minna
authors.identifier: 0000-0002-8288-9442
authors.initials: M
authors.lastname: Honkila
authors.affiliation: PEDEGO Research Unit and Medical Research Center Oulu, University of Oulu, Oulu, Finland.
authors.forename: Erika
authors.initials: E
authors.lastname: Wikström
authors.affiliation: Department of Children and Adolescents, Oulu University Hospital, Oulu, Finland.|PEDEGO Research Unit and Medical Research Center Oulu, University of Oulu, Oulu, Finland.
authors.forename: Marjo
authors.initials: M
authors.lastname: Renko
authors.affiliation: National Institute for Health and Welfare, Oulu, Finland.
authors.forename: Heljä-Marja
authors.initials: HM
authors.lastname: Surcel
authors.affiliation: Department of Children and Adolescents, Oulu University Hospital, Oulu, Finland.|PEDEGO Research Unit and Medical Research Center Oulu, University of Oulu, Oulu, Finland.
authors.forename: Tytti
authors.initials: T
authors.lastname: Pokka
authors.affiliation: Nordlab Oulu, Oulu University Hospital, Oulu, Finland.
authors.forename: Irma
authors.initials: I
authors.lastname: Ikäheimo
authors.affiliation: Department of Children and Adolescents, Oulu University Hospital, Oulu, Finland.|PEDEGO Research Unit and Medical Research Center Oulu, University of Oulu, Oulu, Finland.
authors.forename: Matti
authors.initials: M
authors.lastname: Uhari
authors.affiliation: Department of Children and Adolescents, Oulu University Hospital, Oulu, Finland.|PEDEGO Research Unit and Medical Research Center Oulu, University of Oulu, Oulu, Finland.
authors.forename: Terhi
authors.initials: T
authors.lastname: Tapiainen
mesh_terms: D000328:Adult; D015373:Bacterial Typing Techniques; D002675:Child, Preschool; D002690:Chlamydia Infections / Q000453:epidemiology / Q000635:transmission*; D002692:Chlamydia trachomatis / Q000302:isolation & purification*; D003231:Conjunctivitis / Q000453:epidemiology* / Q000382:microbiology; D005260:Female; D005387:Finland / Q000453:epidemiology; D006801:Humans; D007223:Infant; D007231:Infant, Newborn; D018445:Infectious Disease Transmission, Vertical / Q000517:prevention & control / Q000706:statistics & numerical data*; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000453:epidemiology* / Q000382:microbiology / Q000517:prevention & control; D011336:Probability; D012042:Registries; D018571:Sentinel Surveillance; D055815:Young Adult
keywords: CHILDREN; CHLAMYDIA TRACHOMATIS; EPIDEMIOLOGY (CLINICAL); SEROLOGY