External validation study of a clinical decision aid to reduce unnecessary antibiotic prescriptions in women with acute cystitis

Warren J. McIsaac, Rahim Moineddin, Ildikó Gágyor, Tony Mazzulli

Empirical prescribing of antibiotics to women with symptoms of acute cystitis prior to culture results is common, but subsequent culture results are often negative. A clinical decision aid for prescribing decisions in acute cystitis was previously developed that could reduce these unnecessary antibiotic prescriptions but has not been validated. This study sought to validate this decision aid for empirical antibiotic prescribing decisions in a new cohort of women with suspected acute cystitis. External validation study of a clinical decision aid in 397 women with symptoms of acute cystitis, involving 230 Canadian family practitioners across Canada between 2009 and 2011. The sensitivity and specificity of the decision aid compared to a gold standard positive urine culture (defined as ≥10(2) cfu/ml (≥10(5) CFU/L)) was determined, and compared with physician management, and the earlier development cohort study estimates. Other outcomes assessed were total antibiotic prescriptions, unnecessary antibiotics for negative urine cultures, and recommendations for urine culture testing. Chi-square tests were used for unpaired comparisons, adjusted for physician clustering. McNemar's test was used for paired comparisons. There were 245/397 (61.7%) positive urine cultures. The cystitis aid sensitivity was 202/245 (82.5%, 95% Confidence Interval (CI)) = 77.1%, 86.8%), compared to 167/208 (80.3%) in the previous development cohort (p = 0.54), and 239/245 (97.6%) by family physicians in the current study (p < 0.001). Specificity was low for physicians (10/152, 6.6%) compared to the decision aid (54/152, 35.5%; p < 0.001, resulting in more antibiotic prescriptions by physicians (381/397, 96.0%) than would occur with decision aid recommendations (300/397, 75.6%, p < 0.001). Unnecessary antibiotic prescriptions where urine cultures were negative would be reduced an absolute 11.1% with cystitis aid recommendations (98/397, 24.7%) compared to usual physician care (142/397, 35.8%; p = 0.001). Urine cultures would also be reduced (97/397, 24.4% decision aid vs 351/397, 88.4% physicians; p < 0.001). A 3-item clinical decision aid demonstrated reproducible accuracy in two cohorts of women with acute cystitis symptoms. Clinically important reductions in total and unnecessary antibiotic use, as well as urine culture testing, could result with routine clinical use compared to current empirical physician management practices.