Duration of Group A Streptococcus PCR Positivity Following Antibiotic Treatment of Pharyngitis

Publication date: Available online 12 October 2017
Source:Diagnostic Microbiology and Infectious Disease
Author(s): Jason H. Homme, Corryn S. Greenwood, Lisa B. Cronk, Lisa M. Nyre, James R Uhl, Amy L. Weaver, Robin Patel
BackgroundPolymerase chain reaction (PCR) has high sensitivity and specificity for detection of group A streptococcus (GAS) in throat swabs, and is routinely used for GAS pharyngitis diagnosis at our institution. Herein we defined the natural history of throat swab GAS PCR and culture positivity during and following treatment of GAS pharyngitis.MethodsFifty children with a PCR positive GAS throat swab were recruited for participation. Four additional throat swabs were collected over two weeks following the initial positive PCR result (during and following a standard course of antibiotic therapy) and tested for GAS using rapid real-time PCR and culture.ResultsAfter the initial positive swab, 45% had a positive PCR two to four days, 20% five to seven days, 18% eight to ten days, 25% 11–13days, and 20% 14–18days later. The median time to a negative PCR was four days with the nadir in positive PCR results approximating the end of a typical ten-day treatment interval. Seven subjects remained persistently PCR positive. Culture results remained positive at a stable rate for each time interval, ranging from 5 to 10%.ConclusionsIf a patient presents with symptoms of GAS pharyngitis after previous positive GAS PCR testing and treatment with appropriate antibiotics, it is reasonable to use PCR testing for GAS pharyngitis testing beginning one week after initial testing. Further studies are warranted to determine if this time frame can be applied to PCR testing used to detect other infections.



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