title: Recent infections are associated with decreased risk of rheumatoid arthritis: a population-based case-control study.
abstract: OBJECTIVE
  Do recent infections affect the risk of rheumatoid arthritis (RA)?
  
  
  METHODS
  We used the population-based case-control study EIRA (N=6401) on incident RA and healthy controls, matched for sex, age, calendar period and area of residence. Gastroenteritis, urinary tract infection, genital infection, prostatitis, sinusitis, tonsillitis and pneumonia during the 2 years before inclusion in the study were investigated. Conditional logistic regression was used to calculate OR, adjusting for smoking and socioeconomic status.
  
  
  RESULTS
  Infections in the gastrointestinal and urogenital tract before clinical onset were associated with a lowered risk of RA: gastroenteritis (OR=0.71 (95% CI 0.63 to 0.80)), urinary tract infections (OR=0.78 (95% CI 0.68 to 0.90)) and genital infections (OR=0.80 (95% CI 0.64 to 1.00)), while a non-significant association of similar magnitude was observed for the less common prostatitis (OR=0.64 (95% CI 0.38 to 1.08)). In contrast, no associations were observed for sinusitis, tonsillitis or pneumonia.
  
  
  CONCLUSIONS
  Gastrointestinal and urogenital infections, but not respiratory infections, are associated with a significantly lowered risk of RA. The results indicate that infections in general do not affect the risk for RA, but that certain infections, hypothetically associated with changes in the gut microbiome, could diminish the risk.
authors: Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden Epidemiology and Register Centre South, Skåne University Hospital, Lund, Sweden.
authors: Maria E C
authors: ME
authors: Sandberg
authors: Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
authors: Camilla
authors: C
authors: Bengtsson
authors: Rheumatology Unit, Department of Medicine, Karolinska Institutet/Karolinska University Hospital, Stockholm, Sweden.
authors: Lars
authors: L
authors: Klareskog
authors: Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden.
authors: Lars
authors: L
authors: Alfredsson
authors: Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden Rheumatology Unit, Department of Medicine, Karolinska Institutet/Karolinska University Hospital, Stockholm, Sweden.
authors: Saedis
authors: S
authors: Saevarsdottir
mesh_terms: D000328:Adult; D000368:Aged; D001172:Arthritis, Rheumatoid / Q000453:epidemiology*; D016022:Case-Control Studies; D005260:Female; D005759:Gastroenteritis / Q000453:epidemiology; D006801:Humans; D007239:Infections / Q000453:epidemiology*; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D011014:Pneumonia / Q000453:epidemiology; D011472:Prostatitis / Q000453:epidemiology; D065840:Protective Factors; D060737:Reproductive Tract Infections / Q000453:epidemiology; D012307:Risk Factors; D012852:Sinusitis / Q000453:epidemiology; D011795:Surveys and Questionnaires; D014069:Tonsillitis / Q000453:epidemiology; D014552:Urinary Tract Infections / Q000453:epidemiology
keywords: Epidemiology; Infections; Rheumatoid Arthritis