Evidence that patients with rheumatoid arthritis have asymptomatic ‘non-significant’ Proteus mirabilis bacteriuria more frequently than healthy controls

Objectives: patients with rheumatoid arthritis (RA) are reported to have in their sera raised levels of antibody specific to Proteus mirabilis. The aim of the study was to verify this and to determine an explanation for it by investigating the frequency of P. mirabilis urinary tract infection in RA patients and matched controls. Methods: freshly voided urine was examined for the presence, number and identity of infecting bacteria. The levels of antibody in blood and in urine of the IgM, IgA and IgG classes to the common O serotypes of P. mirabilis and the antigens to which they reacted were determined by enzyme-linked immunosorbent assay (ELISA) and immunoblotting. Results: analysis of urine from 76 patients with RA and 48 age- and gender-matched health controls showed that only two (4%) of the control urines but 25 (33%) of those from the RA patients were infected. The commonest infecting organism in the RA patients' urine was Protein mirabilis which occurred twice as frequently as Escherichia coli. Proteus mirabilis was found in 52% of the infected urines of the RA patients and was always detected as a pure growth and usually in insignificant (