Frequency of triggering bacteria in patients with reactive arthritis and undifferentiated oligoarthritis and the relative importance of the tests used for diagnosis

Objective-Reactive arthritis (ReA) triggered by Chlamydia trachomatis or en teric bacteria such as yersinia, salmonella, Campylobacter jejuni, or shige lla is an important differential diagnosis in patients presenting with the clinical picture of an undifferentiated oligoarthritis (UOA). This study wa s undertaken to evaluate the best diagnostic approach. Patients and methods-52 patients with ReA, defined by arthritis and a sympt omatic preceding infection of the gut or the urogenital tract, and 74 patie nts with possible ReA, defined by oligoarthritis without a preceding sympto matic infection and after exclusion of other diagnoses (UOA), were studied. The following diagnostic tests were applied for the identification of the triggering bacterium: for yersinia induced ReA-stool culture, enzyme immuno assay (EIA), and Widal's agglutination test for detection of antibodies to yersinia; for salmonella or campylobacter induced ReA-stool culture, EIA fo r the detection of antibodies to salmonella and Campylobacter jejuni; for i nfections with shigella-stool culture; for infections with Chlamydia tracho matis-culture of the urogenital tract, microimmunofluorescence and immunope roxidase assay for the detection of antibodies to Chlamydia trachomatis. Results-A causative pathogen was identified in 29/52 (56%) of all patients with ReA. In 17 (52%) of the patients with enteric ReA one of the enteric b acteria was identified: salmonella in 11/33 (33%) and yersinia in 6/33 (18% ). Chlamydia trachomatis was the causative pathogen in 12/19 (63%) of the p atients with urogenic ReA. In patients with the clinical picture of UOA a s pecific triggering bacterium was also identified in 35/74 (47%) patients: y ersinia in 14/74 (19%), salmonella in 9/74 (12%), and Chlamydia trachomatis in 12/74 (16%). Conclusions-Chlamydia trachomatis, yersinia, and salmonella can be identifi ed as the causative pathogen in about 50% of patients with probable or poss ible ReA if the appropriate tests are used.