title: Occurrence of delayed-onset post-traumatic stress disorder: a systematic review and meta-analysis of prospective studies.
abstract: OBJECTIVE
  Post-traumatic stress disorder (PTSD) develops according to consensus criteria within the first 1-6 months after a horrifying traumatic event, but it is alleged that PTSD may develop later. The objective was to review the evidence addressing occurrence of PTSD with onset >6 months after a traumatic event (delayed-onset PTSD).
  
  
  METHODS
  Through a systematic search in PubMed, EMBASE, and PsycINFO, we identified 39 studies with prospective ascertainment of PTSD. A meta-analysis was performed in order to obtain a weighted estimate of the average proportion of delayed-onset PTSD cases, and meta-regression was used to examine effects of several characteristics
  
  
  RESULTS
  Delayed-onset PTSD was reported in all studies except one, and the average prevalence across all follow-up time was 5.6% [95% confidence interval (95% CI) 4.3-7.3%]. The proportion with delayed-onset PTSD relative to all cases of PTSD was on average 24.5% (95% CI 19.5-30.3%) with large variation across studies. In six studies with sub-threshold symptom data, delayed-onset PTSD seemed most likely an aggravation of early symptoms. The proportion with delayed-onset PTSD was almost twice as high among veterans and other professional groups compared to non-professional victims.
  
  
  CONCLUSIONS
  Descriptive follow-up data suggest that PTSD may manifest itself >6 months after a traumatic event, delayed-onset PTSD most often, if not always, is preceded by sub-threshold PTSD symptoms, and a higher proportion of PTSD cases are delayed among professional groups. Contextual factors and biased recall may inflate reporting of PTSD and a cautious interpretation of prevalence rates seems prudent.
authors.affiliation: Department of Occupational and Environmental Medicine, Bispebjerg Bakke 23, Bispebjerg Hospital, Denmark. nicolai.utzon-frank.01@regionh.dk.
authors.forename: Nicolai
authors.initials: N
authors.lastname: Utzon-Frank
authors.forename: Nina
authors.initials: N
authors.lastname: Breinegaard
authors.forename: Mette
authors.initials: M
authors.lastname: Bertelsen
authors.forename: Marianne
authors.initials: M
authors.lastname: Borritz
authors.forename: Nanna Hurwitz
authors.initials: NH
authors.lastname: Eller
authors.forename: Merete
authors.initials: M
authors.lastname: Nordentoft
authors.forename: Kasper
authors.initials: K
authors.lastname: Olesen
authors.forename: Naja Hulvej
authors.initials: NH
authors.lastname: Rod
authors.forename: Reiner
authors.initials: R
authors.lastname: Rugulies
authors.forename: Jens Peter
authors.initials: JP
authors.lastname: Bonde
mesh_terms: D003718:Denmark / Q000453:epidemiology; D006801:Humans; D011446:Prospective Studies; D013313:Stress Disorders, Post-Traumatic / Q000453:epidemiology*