Sore throat in family practice: comparison of blood agar throat culture with a rapid enzyme immunoassay test for diagnostic purposes.

The Ventrescreen (Ventrex) rapid enzyme immunoassay test for detecting group A streptococcal antigen directly from a throat swab was compared with conventional blood agar throat culture in the diagnosis of beta haemolytic streptococcal infection among 311 patients with a sore throat attending a large suburban Jerusalem primary care clinic. Using the throat culture as the 'gold standard' the Ventrescreen test had a sensitivity of 82%, a specificity of 50%, a positive predictive value of 49%, and a negative predictive value of 82% for beta haemolytic streptococcal infection. These results are not good enough for the test to be considered a reliable substitute for throat culture in such a setting. The negative predictive value, however, supports the use of a negative test result to identify those patients in whom antibiotic therapy could be withheld until the result of their throat culture became available. These conclusions are at variance with recommendations from other studies of similar tests in different population groups, and stress the need for the careful evaluation, especially in primary care clinics, of any such rapid test which claims to be able to replace throat culture in the detection of beta haemolytic streptococcal infection.