Objective: The throat culture and rapid antigen tests are frequently used to diagnose group A betahemolytic streptococcal (GAS) pharyngitis. Specimen collection may be carried out by using single throat swabs or by double swabs. Generally, one single throat swab is sent to the laboratory for both tests, it is first used to inoculate culture media and then used for rapid antigen tests. Double swabs provide ease of use by allowing the sample to be taken for both culture and antigen testing at the same time, but it has a higher cost. The aim of the present study was to evaluate the efficiency and necessity of double swabs in detection of GAS by culture and antigen testing.

Method: The throat swab specimens sent to our laboratory with double swab (BD BBL CultureSwab EZ II) between 17.02.2017-27.02.2017 were evaluated prospectively. The second swabs of 100 specimens that were found as positive by antigen testing (BD Veritor™ System Strep A Test) with the first swab were first used for culture, and then reused for antigen testing. The positivity rates in both tests were compared.

Results: A total of 100 antigen positivities were determined in the samples sent with double swabs. GAS was identified by culture in 99 (99%) of these samples. When these 100 samples were retested with the second swab used for culture, antigen positivity decreased to 76 (76%). Of the 100 positive test results, 76 samples had strong bands while the remaining 24 samples showed a relatively weak reaction. Seventy- four of the 76 samples (97%) that produced strong bands, and two of the 24 samples (8%) that formed weak bands were positive with the second swab. It was observed that the culture- negative sample formed a weak band with the first swab and gave a negative result with the second swab.

Conclusion: The use of a single swab for both culture and rapid antigen testing in throat swab specimens significantly reduces the antigen test positivity. Using double swabs could increase the inoculum size and improve the performance of the rapid antigen test facilitating the detection of GAS.