Group A streptococcal infection in patients presenting with a sore throat at an accident and emergency department: prospective observational study.

OBJECTIVES To determine the prevalence of group A streptococcal infection and to evaluate the predictive value of clinical findings and rapid streptococcal antigen detection testing in patients presenting with a sore throat or suspected clinically to have acute pharyngitis. DESIGN Prospective observational study. SETTING Accident and emergency department of a public hospital, Hong Kong. PATIENTS All patients presenting with a sore throat as the chief complaint, or suspected clinically to have acute pharyngitis, from April to September 2000. MAIN OUTCOME MEASURES Demographic data, clinical features, microbiological throat culture results, and rapid streptococcal antigen detection (Accustrip) test results. RESULTS Of 1449 patients recruited during the 6-month study period, only 44 (3.0%) had positive throat cultures for group A beta-haemolytic streptococcus. The majority of group A beta-haemolytic streptococci were isolated from patients between the age of 3 and 60 years. Clinical findings other than an absence of cough were found to be unhelpful in predicting group A beta-haemolytic streptococcal throat infection. The sensitivity of the rapid group A streptococcal antigen detection test was 52.6% and the specificity was 98.2%. CONCLUSIONS The prevalence of group A beta-haemolytic streptococcus in patients presenting with a sore throat, or suspected clinically of having acute pharyngitis, was low. If empirical antibiotics were given to all such patients, 97% of them would be unnecessarily treated. Age and absence of cough were the only clinical findings helpful in predicting the presence of group A beta-haemolytic streptococcal throat infection. The rapid group A streptococcal antigen detection test can provide a quick guide to clinicians on the necessity of antibiotic therapy. However, a confirmatory throat culture backup is recommended for patients with a negative test result.