Early antibiotic treatment of reactive arthritis associated with enteric infections: clinical and serological study. OBJECTIVE--To find out whether a 10-14 days' course of antibiotics early in the course of reactive arthritis associated with enteric infections could reduce the severity and duration of the disease and whether the antibody response in patients with reactive arthritis associated with yersinia infection differed between those treated and those not treated with the antibiotics. DESIGN--Prospective multicentre trial in which patients were randomised to treatment or no treatment with antibiotics. Patients were seen at three and six weeks and three, six, nine, 12, and 18 months after their first visit. SETTING--Departments of infectious diseases in three hospitals in Linkoping, Malmo, and Stockholm, Sweden. PATIENTS--40 Consecutive patients who had had symptoms of reactive arthritis associated with enteric infection for less than four weeks. INTERVENTIONS--20 Patients were allocated to treatment with antibiotics and 20 patients did not receive antibiotics. All patients received non-steroidal anti-inflammatory drugs, and four also received intra-articular steroid injections after at least six weeks' observation. MAIN OUTCOME MEASURES--Arthritic symptoms assessed clinically and by using Ritchies' index; blood measurements reflecting inflammatory activity; serum IgG, IgM, and IgA antibody titres; HLA tissue type. RESULTS--No difference was observed concerning duration of arthritis, grade of inflammation, and number of joints affected between patients treated and those not treated with antibiotics. Furthermore, there was no significant difference between the two groups in erythrocyte sedimentation rate and haptoglobin, IgG, and IgA concentrations. All values had returned to normal within three months. No patient developed chronic arthritis, but sustained slight arthralgia occurred in three patients. The HLA-B27 antigen was found in 23 (58%) of the patients, and its presence did not affect clinical outcome. The IgG, IgM, and IgA antibody responses were similar in patients treated with antibiotics and those not treated. CONCLUSION--Short term antibiotic treatment has no beneficial effect on the clinical outcome of reactive arthritis associated with enteric infection. 