Editing Rheumatoid arthritis (section)

===Negative findings===
No infectious agent has been consistently linked with RA and there is no evidence of disease clustering to indicate its infectious cause,<ref name="Elsevier">{{cite book| vauthors = Doherty M, Lanyon P, Ralston SH |title=Musculosketal Disorders-Davidson's Principle of Internal Medicine| publisher=Elsevier|pages=1100–1106|edition=20th}}</ref> but [[periodontal disease]] has been consistently associated with RA.<ref name=Lancet2016/>

The many negative findings suggest that either the trigger varies, or that it might, in fact, be a chance event inherent with the immune response.<ref>{{cite journal | vauthors = Edwards JC, Cambridge G, Abrahams VM | title = Do self-perpetuating B lymphocytes drive human autoimmune disease? | journal = Immunology | volume = 97 | issue = 2 | pages = 188–196 | date = June 1999 | pmid = 10447731 | pmc = 2326840 | doi = 10.1046/j.1365-2567.1999.00772.x }}{{subscription required}}</ref>