Can a clinical rule accurately predict whether a patient has strep throat?

BACKGROUND: Injudicious use of antibiotics in the management of sore throat contributes to the proliferation of resistant organisms and exposes patients to adverse effects of unnecessary medication. A clinical decision-making tool that better identifies patients with streptococcal infection would decrease unnecessary testing and antibiotic therapy. The authors of this study evaluated the validity of such a clinical rule in a primary care setting.

POPULATION STUDIED: Family physicians in Ontario, Canada, enrolled 621 patients, all of whom presented with a sore throat and an upper respiratory infection. Of these, two thirds were women and one fourth were aged younger than 15 years. Exclusion criteria included age younger than 3 years, recent treatment with antibiotics, or an alternate diagnosis that explains the symptoms (eg, otitis media, pneumonia).

STUDY DESIGN AND VALIDITY: The authors compared the results of a clinical rule with the independent clinical decisions of the treating physician. Physicians evaluated and treated patients per their usual routine and recorded their findings and interventions on an assessment form. Throat cultures were obtained for all patients. The physicians also recorded the “strep” score for each patient. This rule assigns 1 point for each of the following symptoms: temperature greater than 38°C, absence of cough, tender anterior cervical adenopathy, tonsillar swelling or exudate, and age younger than 15 years. One point is subtracted for age older than 45 years. A score of 1 or less was considered negative, and neither throat culture nor antibiotic therapy was recommended. A score of 2 or 3 was considered indeterminate, and a throat culture was recommended with antibiotic therapy based on culture results. A score of 4 or greater was considered positive, and antibiotic therapy or throat culture was recommended. Comparison of the number of antibiotic prescriptions and throat cultures was made between the physicians’ plan and the clinical rule.

OUTCOMES MEASURED: The primary outcomes were the sensitivity and specificity of the clinical rule. Concordance of antibiotic treatment and throat culture results was evaluated.

RESULTS: Physicians prescribed antibiotics to 27.9% of patients. Of these, only 37% had group A streptococcus (GAS) on culture. Cultures were positive for GAS in 17% of all patients. The clinical rule was 85% sensitive for identifying GAS infection (95% confidence interval [CI], 76.5%-91.4%) and 92.1% specific (95% CI, 89.3%-94.3%). Few patients with a clinical rule score of 1 or less had GAS pharyngitis (4.7%). The prevalence of GAS was 17% for a score of 2, 35% for a score of 3, and 51% for a score of 4 or more. Use of the clinical rule would have reduced antibiotic use by 52.3% and throat culture by 35.8% in all patients. Although this effect was more notable in adult patients, even in children the score was more sensitive than the clinical assessment and would have reduced unnecessary testing.

BACKGROUND: Injudicious use of antibiotics in the management of sore throat contributes to the proliferation of resistant organisms and exposes patients to adverse effects of unnecessary medication. A clinical decision-making tool that better identifies patients with streptococcal infection would decrease unnecessary testing and antibiotic therapy. The authors of this study evaluated the validity of such a clinical rule in a primary care setting.

POPULATION STUDIED: Family physicians in Ontario, Canada, enrolled 621 patients, all of whom presented with a sore throat and an upper respiratory infection. Of these, two thirds were women and one fourth were aged younger than 15 years. Exclusion criteria included age younger than 3 years, recent treatment with antibiotics, or an alternate diagnosis that explains the symptoms (eg, otitis media, pneumonia).

STUDY DESIGN AND VALIDITY: The authors compared the results of a clinical rule with the independent clinical decisions of the treating physician. Physicians evaluated and treated patients per their usual routine and recorded their findings and interventions on an assessment form. Throat cultures were obtained for all patients. The physicians also recorded the “strep” score for each patient. This rule assigns 1 point for each of the following symptoms: temperature greater than 38°C, absence of cough, tender anterior cervical adenopathy, tonsillar swelling or exudate, and age younger than 15 years. One point is subtracted for age older than 45 years. A score of 1 or less was considered negative, and neither throat culture nor antibiotic therapy was recommended. A score of 2 or 3 was considered indeterminate, and a throat culture was recommended with antibiotic therapy based on culture results. A score of 4 or greater was considered positive, and antibiotic therapy or throat culture was recommended. Comparison of the number of antibiotic prescriptions and throat cultures was made between the physicians’ plan and the clinical rule.

OUTCOMES MEASURED: The primary outcomes were the sensitivity and specificity of the clinical rule. Concordance of antibiotic treatment and throat culture results was evaluated.

RESULTS: Physicians prescribed antibiotics to 27.9% of patients. Of these, only 37% had group A streptococcus (GAS) on culture. Cultures were positive for GAS in 17% of all patients. The clinical rule was 85% sensitive for identifying GAS infection (95% confidence interval [CI], 76.5%-91.4%) and 92.1% specific (95% CI, 89.3%-94.3%). Few patients with a clinical rule score of 1 or less had GAS pharyngitis (4.7%). The prevalence of GAS was 17% for a score of 2, 35% for a score of 3, and 51% for a score of 4 or more. Use of the clinical rule would have reduced antibiotic use by 52.3% and throat culture by 35.8% in all patients. Although this effect was more notable in adult patients, even in children the score was more sensitive than the clinical assessment and would have reduced unnecessary testing.

BACKGROUND: Injudicious use of antibiotics in the management of sore throat contributes to the proliferation of resistant organisms and exposes patients to adverse effects of unnecessary medication. A clinical decision-making tool that better identifies patients with streptococcal infection would decrease unnecessary testing and antibiotic therapy. The authors of this study evaluated the validity of such a clinical rule in a primary care setting.

POPULATION STUDIED: Family physicians in Ontario, Canada, enrolled 621 patients, all of whom presented with a sore throat and an upper respiratory infection. Of these, two thirds were women and one fourth were aged younger than 15 years. Exclusion criteria included age younger than 3 years, recent treatment with antibiotics, or an alternate diagnosis that explains the symptoms (eg, otitis media, pneumonia).

STUDY DESIGN AND VALIDITY: The authors compared the results of a clinical rule with the independent clinical decisions of the treating physician. Physicians evaluated and treated patients per their usual routine and recorded their findings and interventions on an assessment form. Throat cultures were obtained for all patients. The physicians also recorded the “strep” score for each patient. This rule assigns 1 point for each of the following symptoms: temperature greater than 38°C, absence of cough, tender anterior cervical adenopathy, tonsillar swelling or exudate, and age younger than 15 years. One point is subtracted for age older than 45 years. A score of 1 or less was considered negative, and neither throat culture nor antibiotic therapy was recommended. A score of 2 or 3 was considered indeterminate, and a throat culture was recommended with antibiotic therapy based on culture results. A score of 4 or greater was considered positive, and antibiotic therapy or throat culture was recommended. Comparison of the number of antibiotic prescriptions and throat cultures was made between the physicians’ plan and the clinical rule.

OUTCOMES MEASURED: The primary outcomes were the sensitivity and specificity of the clinical rule. Concordance of antibiotic treatment and throat culture results was evaluated.

RESULTS: Physicians prescribed antibiotics to 27.9% of patients. Of these, only 37% had group A streptococcus (GAS) on culture. Cultures were positive for GAS in 17% of all patients. The clinical rule was 85% sensitive for identifying GAS infection (95% confidence interval [CI], 76.5%-91.4%) and 92.1% specific (95% CI, 89.3%-94.3%). Few patients with a clinical rule score of 1 or less had GAS pharyngitis (4.7%). The prevalence of GAS was 17% for a score of 2, 35% for a score of 3, and 51% for a score of 4 or more. Use of the clinical rule would have reduced antibiotic use by 52.3% and throat culture by 35.8% in all patients. Although this effect was more notable in adult patients, even in children the score was more sensitive than the clinical assessment and would have reduced unnecessary testing.