title: Seasonal variation in Guillain-Barré syndrome: a systematic review, meta-analysis and Oxfordshire cohort study.
abstract: BACKGROUND
  Evidence for seasonal variation in incidence and subtype of Guillain-Barré syndrome (GBS) is contradictory, but has implications for provision of neurological services and understanding pathogenesis.
  
  
  METHODS
  We searched PubMed and EMBASE between inception and January 2014, including all studies reporting seasonal incidence of GBS. We included a retrospective cohort study of patients with GBS at the John Radcliffe Hospital, Oxford 2001-2012 and determined the seasonal variation in GBS incidence and length of stay. The incidence rate ratio (IRR) for winter versus summer was pooled across studies by fixed and random effects meta-analysis weighted by inverse variance, stratified by geographical region, infectious prodrome and GBS subtype.
  
  
  RESULTS
  Across 9836 patients from 42 studies there was a 14% increased risk of GBS in winter versus summer (IRR=1.14, 1.02-1.27, p=0.020), with significant heterogeneity between studies (I(2)=77%, p<0.0001), including significant seasonal variation in Oxford (n=140; p=0.037) for winter versus summer (IRR=1.92, 1.18-3.11, p=0.004) but a non-significantly reduced length of stay for winter versus other seasons (15 vs 21 days, p=0.08). Across all studies, there was greater seasonal variation with respiratory prodrome (IRR=3.06, 1.84-5.11, p<0.0001) than diarrhoeal prodrome (IRR=1.10, 0.60-2.00, p=0.76) and a greater incidence in winter in Western countries (IRR=1.28), the Far East (IRR=1.20) and Middle East (IRR=1.12), with a lower incidence in the Indian subcontinent (IRR=0.86) and Latin America (IRR=0.75).
  
  
  CONCLUSIONS
  Incidence of GBS was greater in winter than summer, but this was not evident in all geographical regions. This is likely to be related to regional variation in prodromal illnesses.
authors.affiliation: Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
authors.forename: Alastair J S
authors.initials: AJ
authors.lastname: Webb
authors.affiliation: Addenbrooke's Hospital, University of Cambridge, UK.
authors.forename: Susannah A E
authors.initials: SA
authors.lastname: Brain
authors.affiliation: Clinical Imaging Sciences Centre, Brighton and Sussex Medical School, University of Sussex, UK.
authors.forename: Ruth
authors.initials: R
authors.lastname: Wood
authors.affiliation: Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
authors.forename: Simon
authors.initials: S
authors.lastname: Rinaldi
authors.affiliation: Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford, UK.
authors.forename: Martin R
authors.initials: MR
authors.lastname: Turner
mesh_terms: D000328:Adult; D015331:Cohort Studies; D005260:Female; D020275:Guillain-Barre Syndrome / Q000453:epidemiology / Q000503:physiopathology*; D006801:Humans; D015994:Incidence; D007902:Length of Stay; D008297:Male; D008875:Middle Aged; D012189:Retrospective Studies; D012621:Seasons; D006113:United Kingdom / Q000453:epidemiology
keywords: EPIDEMIOLOGY; GUILLAIN-BARRE SYNDROME; NEUROPATHY