Antibody-coated bacteria in urine: criterion for a positive test and its value in defining a higher risk of treatment failure.

Midstream urines from 237 patients with significant bacteriuria were examined for antibody-coated bacteria (ACB): 113 urines gave a positive result. When more than 25 000 organisms from the ACB-positive urines were scanned either fewer than 100 or more than 250 fluorescent bacteria (ie, greater than 1%) were found: thus the distribution of the fluorescent bacteria was bimodal. To compare the effectiveness of therapy in patients with ACB-positive and ACB-negative bacteriuria, 120 randomly selected patients were given a 7-day course of appropriate therapy. The results were assessed after 6 weeks. In 66 ACB-negative patients the cure rate was 84.8%, which was not significantly different from that found in 26 patients (80.7%) whose urine contained ACB in small numbers (less than 1%). In contrast, in 28 patients whose urine contained greater than 1% ACB the cure rate was only 36%. There was no correlation between the immunoglobulin class coating the bacteria and the response to treatment. The presence of greater than 1% ACB in the midstream urine thus identifies patients who are at high risk of treatment failure.