The Strep A test is reliable even after a sore throat has been treated with penicillin

self report. The effect of antibiotics in relieving sore throat symptoms is seen mainly in patients with more severe symptoms and group A streptococcus in the throat. According to Swedish treatment recommendations, penicillin V prescription is limited to patients with at least 3 Centor criteria (fever, painful swelling of lymph nodes in the corners of the jaw, redness of the tonsils with sedimentation and no cough) and a positive Streptococcus group A antigen test (Strep A test ).

It is suspected that residual antigen from killed group A streptococcus may result in false positive Strep A tests in patients following penicillin therapy for streptococcal tonsillitis. In a new study, we examined Strep A testing and throat culture in patients recently treated with penicillin V for tonsillitis. [1]. The study was conducted within a randomized controlled trial of 5 and 10 days of penicillin treatment of streptococcal tonsillitis. [2]. We included 316 patients who all 1) had at least 3 Centor criteria, a positive Strep A test, a positive Group A Streptococcus throat culture at baseline, and 2) attended a follow-up visit within 21 days of starting treatment where fresh throat swabs were taken from Order Strep A and culture.

We found that the Strep A test and throat culture at the follow-up visit agreed in 91 percent (286/316) of cases. The log-rank test showed no difference between the results of the rapid test and the results of the swallow culture. Only 3 of the patients had a negative Strep A test when the culture was positive. 27 patients had a positive rapid test and a negative culture. We found no association between concordance of test results and duration of treatment (5 or 10 days with penicillin V), time between initiation of treatment and follow-up visit, any pharyngeal symptoms at follow-up, gender or age over/under 15 years. Both the Strep A test and the throat culture indicated a slightly elevated level of transmissibility of group A streptococcus in healthy subjects at follow-up.

Our results are consistent with previous studies showing that group A streptococcal antigen tests have higher sensitivity than conventional throat culture, but we cannot rule out that occasional positive Strep A tests were caused by residual material from the killed bacteria. Our conclusion is that the Strep A test is reliable even after recent penicillin treatment for tonsillitis. Because antibiotics are often prescribed while awaiting throat culture results, a rapid negative test for group A streptococcus can prevent patients from receiving unnecessary antibiotic treatments for recurrent throat infections.