Towards a better diagnosis of throat infections (with group A beta-haemolytic streptococcus) in general practice

Abstract

Background: Sore throat is a common complaint in general practice. However, management strategies are not very clear. A better diagnostic procedure is needed to prevent the overuse of antibiotics.

Aim: To assess the diagnostic value of a rapid streptococcal antigen detection test in addition to four clinical features in patients with sore throat, using throat culture and antibody titres as reference tests.

Method: Four clinical features [fever (history) > or = 38.0 degrees C, lack of cough, tonsillar exudate, and anterior cervical lymphadenopathy] were registered in 558 patients aged 4 to 60 years presenting with sore throat of no more than 14 days' duration. A rapid diagnostic test was performed, as well as a throat culture and antibody titres [fourfold increase in anti-streptolysin-O (ASO) and/or anti-deoxyribonuclease B (anti-DNAase B)] in patients aged 11 years and older.

Results: Throat cultures were positive for group A beta-haemolytic streptococcus (GABHS) in 33% of the patients. Rapid tests were positive in 24%. Compared with the throat culture, the sensitivity of the rapid test was 65%, the specificity 96%, the positive predictive value 88%, and the negative predictive value 85%. However, for patients with three or four clinical features, the sensitivity of the rapid test was considerably higher at 75%. Children (< or = 14 years) had a slightly raised specificity and raised positive predictive value and prevalence. With the antibody titres as a reference, the rapid test performed as well as the throat culture with regard to its predictive value.

Conclusion: For the management of patients with sore throat in general practice, a rapid test may have an additional value, especially in patients with a high chance of having GABHS infection. However, as the sensitivity of the test studied is low, tests with a higher sensitivity are needed.