title: Temporal relationship between environmental influenza A and Epstein-Barr viral infections and high multiple sclerosis relapse occurrence.
abstract: BACKGROUND
  Multiple sclerosis (MS) relapses have been associated with viral and bacterial infection epidemics in MS patients who have not used interferon.
  
  
  OBJECTIVE
  We studied whether environmental viral infections in the general population can be associated with increased MS relapse occurrence using retrospective data from 1986 to 1995 when interferons were not yet available.
  
  
  METHODS
  Logistic regression modelling was used to compare retrospectively the monthly relapse occurrence from 407 MS patients in Turku University hospital archives and data on ten different specifically diagnosed viral infection epidemics in the general population of Southwestern Finland from 1986 to 1995. The outcome was the odds ratio (OR) of very high relapse occurrence versus low relapse occurrence, or moderate versus low relapse occurrence.
  
  
  RESULTS
  After a peak in diagnosed influenza A cases in the general population, the MS relapse occurrence was 6.5 times more likely to be very high (95% CI 1.8-24.0) and 7.1 times more likely to be moderately high (95% CI 1.5-33.2). An increase in MS relapse counts also followed Epstein-Barr virus (EBV) infections (OR 4.4, 95% CI 1.3-15.1), but we found no significant association with adenovirus infections and MS relapses. The MS relapse occurrence was lowest in the summer months July-August (Chi-square test, p<0.01).
  
  
  CONCLUSIONS
  Our findings suggest that influenza A and EBV viral infections in the general population are associated with a higher occurrence of exacerbations in MS patients, and thus environmental infection data should be included in epidemiological models on MS relapses.
authors.affiliation: Aerobiology Unit, University of Turku, Finland. mervi.oikonen@utu.fi
authors.forename: Mervi
authors.initials: M
authors.lastname: Oikonen
authors.forename: Mikko
authors.initials: M
authors.lastname: Laaksonen
authors.forename: Ville
authors.initials: V
authors.lastname: Aalto
authors.forename: Jorma
authors.initials: J
authors.lastname: Ilonen
authors.forename: Reijo
authors.initials: R
authors.lastname: Salonen
authors.forename: Juha-Pekka
authors.initials: JP
authors.lastname: Erälinna
authors.forename: Martin
authors.initials: M
authors.lastname: Panelius
authors.forename: Aimo
authors.initials: A
authors.lastname: Salmi
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D016009:Chi-Square Distribution; D020031:Epstein-Barr Virus Infections / Q000175:diagnosis / Q000453:epidemiology* / Q000821:virology; D005387:Finland / Q000453:epidemiology; D006785:Hospitals, University; D006801:Humans; D009980:Influenza A virus / Q000472:pathogenicity*; D007251:Influenza, Human / Q000175:diagnosis / Q000453:epidemiology* / Q000821:virology; D016015:Logistic Models; D008875:Middle Aged; D020528:Multiple Sclerosis, Chronic Progressive / Q000175:diagnosis / Q000453:epidemiology* / Q000821:virology; D020529:Multiple Sclerosis, Relapsing-Remitting / Q000175:diagnosis / Q000453:epidemiology* / Q000382:microbiology; D016017:Odds Ratio; D011379:Prognosis; D012189:Retrospective Studies; D018570:Risk Assessment; D012307:Risk Factors; D012621:Seasons; D013997:Time Factors; D055815:Young Adult