• Karin Rystedt, Katarina Hedin, Mia Tyrstrup, Gunilla Skoog-Ståhlgren, Charlotta Edlund, Christian G Giske, Ronny Gunnarsson, and Pär-Daniel Sundvall.
• Research, Education, Development & Innovation, Primary Health Care, Region Västra Götaland, Sweden.
• Scand J Prim Health Care. 2023 Mar 1; 41 (1): 919791-97.

ObjectiveThe aim was to compare rapid antigen detection test (RADT) and throat culture for group A streptococci (GAS) among patients recently treated with penicillin V for GAS pharyngotonsillitis.Design And SettingThe study was a secondary analysis within a randomized controlled trial comparing 5 versus 10 days of penicillin V for GAS pharyngotonsillitis. Patients were recruited at 17 primary health care centres in Sweden.SubjectsWe included 316 patients ≥ 6 years of age, having 3-4 Centor criteria, a positive RADT and a positive throat culture for GAS at inclusion, and also having a RADT and throat culture for GAS taken at a follow-up visit within 21 days.Main Outcome MeasuresRADT and conventional throat culture for GAS.ResultsThis prospective study showed 91% agreement between RADT and culture at follow-up within 21 days. Only 3/316 participants had negative RADT with a positive throat culture for GAS at follow-up, and 27/316 patients with positive RADT had a negative culture for GAS. Log rank test did not reveal any difference in the decline over time of positive tests between RADT and throat culture (p = 0.24). Agreement between RADT and throat culture for GAS at the follow-up was not associated with treatment duration, number of days from inclusion until follow-up, throat symptoms at follow-up, gender, or age.ConclusionRADT and culture for GAS agreed to a high extent also after recent penicillin V treatment. RADT for GAS means a low risk for missing the presence of GAS.KEY POINTSTesting for group A streptococci (GAS) before antibiotic treatment can reduce antibiotic prescription for pharyngotonsillitis. It has been proposed that rapid antigen detection tests (RADT) for group A streptococci after recent penicillin V treatment may be falsely positive due to possible persisting antigens from non-viable bacteria.The decline of the presence of GAS was similar between RADT and conventional throat culture in patients who had recently completed penicillin V treatment for GAS pharyngotonsillitisRADT for GAS is useful in identifying the presence of GAS after recent penicillin V treatment.

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