title: Risk factors for transmission of Ebola or Marburg virus disease: a systematic review and meta-analysis.
abstract: BACKGROUND
  The Ebola virus disease outbreak that started in Western Africa in 2013 was unprecedented because it spread within densely populated urban environments and affected many thousands of people. As a result, previous advice and guidelines need to be critically reviewed, especially with regard to transmission risks in different contexts.
  
  
  METHODS
  Scientific and grey literature were searched for articles about any African filovirus. Articles were screened for information about transmission (prevalence or odds ratios especially). Data were extracted from eligible articles and summarized narratively with partial meta-analysis. Study quality was also evaluated.
  
  
  RESULTS
  A total of 31 reports were selected from 6552 found in the initial search. Eight papers gave numerical odds for contracting filovirus illness; 23 further articles provided supporting anecdotal observations about how transmission probably occurred for individuals. Many forms of contact (conversation, sharing a meal, sharing a bed, direct or indirect touching) were unlikely to result in disease transmission during incubation or early illness. Among household contacts who reported directly touching a case, the attack rate was 32% [95% confidence interval (CI) 26-38%]. Risk of disease transmission between household members without direct contact was low (1%; 95% CI 0-5%). Caring for a case in the community, especially until death, and participation in traditional funeral rites were strongly associated with acquiring disease, probably due to a high degree of direct physical contact with case or cadaver.
  
  
  CONCLUSIONS
  Transmission of filovirus is unlikely except through close contact, especially during the most severe stages of acute illness. More data are needed about the context, intimacy and timing of contact required to raise the odds of disease transmission. Risk factors specific to urban settings may need to be determined.
authors.affiliation: Norwich Medical School, University of East Anglia, Norwich, UK.
authors.forename: Julii
authors.initials: J
authors.lastname: Brainard
authors.affiliation: Norwich Medical School, University of East Anglia, Norwich, UK.
authors.forename: Lee
authors.initials: L
authors.lastname: Hooper
authors.affiliation: Robens Centre for Public and Environmental Health, University of Surrey, Guildford, UK.
authors.forename: Katherine
authors.initials: K
authors.lastname: Pond
authors.affiliation: School of Biological Sciences, University of East Anglia, Norwich, UK.
authors.forename: Kelly
authors.initials: K
authors.lastname: Edmunds
authors.affiliation: Norwich Medical School, University of East Anglia, Norwich, UK Paul.Hunter@uea.ac.uk.
authors.forename: Paul R
authors.initials: PR
authors.lastname: Hunter
mesh_terms: D000818:Animals; D003710:Demography; D004196:Disease Outbreaks / Q000266:history*; D019142:Hemorrhagic Fever, Ebola / Q000453:epidemiology* / Q000635:transmission*; D049674:History, 21st Century; D006801:Humans; D008379:Marburg Virus Disease / Q000453:epidemiology* / Q000635:transmission*; D016017:Odds Ratio; D012307:Risk Factors
keywords: Ebola virus disease; Marburg virus; bodily fluids; risk factors; systematic review