title: Delayed posttraumatic stress disorder: systematic review, meta-analysis, and meta-regression analysis of prospective studies.
abstract: OBJECTIVE
  Prevalence estimates of delayed posttraumatic stress disorder (PTSD) have varied widely in the literature. This study is the first to establish the prevalence of delayed PTSD in prospective studies and to evaluate associated factors through meta-analytic techniques.
  
  
  METHODS
  Studies were located by an electronic search using the databases EMBASE, MEDLINE, and PsycINFO. Search terms were posttraumatic stress disorder [include all subheadings] AND (delayed OR prospective OR longitudinal OR follow-up). Results were limited to journal articles published between 1980 and April 4, 2008.
  
  
  METHODS
  We included longitudinal, prospective studies of humans exposed to a potentially traumatic event that assessed participants at 1 to 6 months after the event, that included a follow-up of at least 12 months after the event, and that specified rates of new onset and remission between assessments in study completers.
  
  
  METHODS
  Data were extracted concerning the study design, demographic features, and event-related characteristics and the number of PTSD cases at first assessment, the number of PTSD cases among study dropouts, and the number of new event-related PTSD cases at each subsequent assessment among study completers. Data from 24 studies were included. Four of these provided additional data on initial subthreshold PTSD and subsequent risk of delayed PTSD.
  
  
  RESULTS
  The proportion of PTSD cases with delayed PTSD was 24.8% (95% CI = 22.6% to 27.2%) after adjusting for differences in study methodology, demographic features, and event-related characteristics. Military combat exposure, Western cultural background, and lower cumulative PTSD incidence were associated with delayed PTSD. Participants with initial subthreshold PTSD were at increased risk of developing delayed PTSD.
  
  
  CONCLUSIONS
  Delayed PTSD was found among about a quarter of PTSD cases and represents exacerbations of prior symptoms.
authors.affiliation: Centrum '45, Nienoord 5, 1112 XE Diemen, The Netherlands. g.smid@centrum45.nl
authors.forename: Geert E
authors.initials: GE
authors.lastname: Smid
authors.forename: Trudy T M
authors.initials: TT
authors.lastname: Mooren
authors.forename: Roos C
authors.initials: RC
authors.lastname: van der Mast
authors.forename: Berthold P R
authors.initials: BP
authors.lastname: Gersons
authors.forename: Rolf J
authors.initials: RJ
authors.lastname: Kleber
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D015995:Prevalence; D011446:Prospective Studies; D012044:Regression Analysis; D013313:Stress Disorders, Post-Traumatic / Q000175:diagnosis / Q000453:epidemiology*