Streptococcal Throat Infection: Calculation of Test Standards and a Comparison between an Antigen Detection Test and Culture

Abstract

The standard minimum sensitivity (94%) and minimum specificity (89%) of a group A streptococcus (GAS) test were calculated, assuming that no more than 10% false positive and no more than 2% false negative test results should be allowed. The clinical judgement of the need for immediate antibiotic treatment in tonsillitis/pharyngitis was an unreliable indicator of a GAS aetiology, 20–29% of the results being false positive and 2–10% false negative. The rapid antigen detection test Tandem Icon Strep A was not sensitive enough to be used as a single test, though it was specific enough. The sensitivity of culture almost reached the standard demand. Two combinations of rapid test and culture (sequence testing) were superior to the rapid test, but were not significantly better than culture.

Key Words:

• streptococcal tonsillitis/pharyngitis
• calculation of test standards
• efficacy of antigen detection test and culture