Methods
In the fall of 1998, a sample of family physicians in the province of Ontario were invited to participate in a trial to reduce antibiotic use in patients with a sore throat. Physicians who had previously participated in practice-based research projects for the College of Family Physicians of Canada and a random sample from the College’s general membership listing were contacted. Those who mailed back a reply card indicating that they wished to participate were randomized to either an intervention or a control group. The study was approved by the University of Toronto Ethics Review Committee.
Both groups of physicians received, by mail, an article describing the clinical score management approach19; a laminated pocket card summarizing the method; clinical encounter and patient consent forms; and a 1-page survey of practice characteristics. Each physician was asked to enroll 8 patients aged 3 years or older whom they believed to have a new URTI with a sore throat. No attempt was made to further define an eligible presentation to encourage physicians to enroll cases representative of their usual practice. Patients were ineligible if they had taken antibiotics during the previous week, were immunocompromised, or could not understand English. Parents were asked to provide consent for children younger than 16 years of age.
A brief standardized assessment form was completed by the physician for each patient and a throat swab was obtained. The throat swab was submitted to the physician’s local laboratory. A copy of the culture result was forwarded to the study center. Treatment decisions and the management of subsequent culture results were the responsibility of the treating physician.
In the intervention group, physicians were provided with a sticker to apply to the encounter form that listed the score management approach. The sticker contained boxes to be checked by the physicians to calculate the score total and determine appropriate management. Physicians not wishing to use the sticker were prompted on the form to write the score total in a space provided. As a result, physicians in the intervention group received repeated prompts that reminded them to use the score approach each time they completed a clinical encounter form. The control group completed a similar form but without either the sticker or the chart prompts.
The details of the clinical score approach have been previously published.19,25 Briefly, 4 clinical findings (fever > 38°C, absence of cough, tender anterior cervical adenopathy, tonsillar swelling or exudate) and age < 15 years are each assigned 1 point and totaled. One point is subtracted for age 45 years or more. Explicit recommendations for management are linked to score totals. If the score total is 1 or less, no throat swab or antibiotic is indicated. A throat swab is recommended for a score of 2 or 3 and an antibiotic only if the culture is positive. Either initiating treatment with an antibiotic or taking a throat swab is appropriate for a score of 4 or more.
The main outcome for the study was the prescription of unnecessary antibiotics, defined as a prescription for antibiotic medication given to a patient whose subsequent throat culture was negative for group A streptococcus. The secondary outcome was overall antibiotic use. The sample size was calculated to detect a 30% decrease in unnecessary antibiotic use (2-sided = 0.05, 1- = 0.90), assuming a 40% baseline prescription rate9 and a 70% negative culture rate.1719 Because groups of patients were treated by the same physician, the sample size was adjusted to take the clustered sampling design into account.36 The intraclass correlation coefficient for prescribing estimated from an earlier study was 0.07.19 Assuming an average of 5 patients assessed per physician, the sample size was estimated to be 85 physicians and 425 patients in each group.
The clinical characteristics of patients in the intervention and control groups were compared with a chi-square test for categorical variables and a t-test for continuous variables. Associations between prescription rates and the practice and demographic characteristics of the physicians were assessed and adjusted for the clustered sampling with Stata Statistical Software (Release 6, Stata Corp., College Station, Tex.). While clustering improves the efficiency of sampling by requiring participation by fewer physicians, confidence intervals that do not account for the design effect are too narrow. Multiple logistic regression was used to adjust for differences in patient and physician characteristics, taking into account the patient clusters by physician in estimating the effect of the intervention.
Results
One hundred sixty-four physicians agreed to participate and were randomized. Of these, only 97 (59.1%) completed the study and provided patient data (Figure). An equal proportion of physicians in the intervention group (40.2%) and control group (41.5%, P = .87) failed to complete the study. No significant differences were identified between the sex or age of physicians who participated and those who did not participate. Of the participating physicians, 86 (84.3%) returned surveys describing their practice settings.