Table 2

Criteria used for the identification of the triggering bacterium as a probable or possible cause of reactive arthritis (ReA); always in the presence of an arthritis either asymmetrically or predominantly of the legs

	Chlamydia	Yersinia	Salmonella	Campylobacter
Probable ReA^2-150		Chlamydia positive in urogenital smearplus symptomatic urethritis	Yersinia positive stool culture	Salmonella positive stool culture	Camplyobacter positive stool culture

		IgG ⩾1/64plus positive IgA or IgM^2-151 plus chlamydia positive in urogenital smear or symptomatic urethritis	Antibody titres of 3 SD above normal^2-151 for IgG plus IgA or IgM	Antibody titres of 3 SD above normal^2-151 for IgG plus IgA or IgM	Antibody titres of 3 SD above normal^2-151 for IgGplus IgA or IgM
	Antibody titres of 2 SD above normal^2-151 for IgG plus IgA or IgMplus symptomatic enteritisor Widal agglutination ⩾1/320 (normal <1/160)	Antibody titres of 2 SD above normal^2-151 for IgGplus IgA or IgMplus symptomatic enteritis	Antibody titres of 2 SD above normal^2-151 for IgG plusIgA or IgM plus symptomatic enteritis
Possible ReA	Chlamydia positive in urogenital smear or IgG ⩾1/64 plus positive IgA or IgM^2-151	Antibody titres of 2 SD above normal^2-151 for IgGplus IgA or IgMor Widal agglutination >1/320 (normal <1/160)	Antibody titres of 2 SD above normal^2-151 for IgGplus IgA or IgM	Antibody titres of 2 SD above normal^2-151 for IgG plus IgA or IgM

↵2-150 Only one of the criteria has to be fulfilled.
↵2-151 As defined in the “Patients and methods” section; SD = standard deviation.