Agreement between rapid antigen detection test and culture for group A streptococcus in patients recently treated for pharyngotonsillitis - a prospective observational study in primary care

Abstract

Objective

The 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 setting

The 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.

Subjects

We 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 measures

RADT and conventional throat culture for GAS.

Results

This 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.

Conclusion

RADT 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 POINTS

• Testing 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 pharyngotonsillitis

• RADT for GAS is useful in identifying the presence of GAS after recent penicillin V treatment

Keywords:

• Streptococcal pharyngotonsillitis
• rapid antigen detection test
• primary care

Acknowledgements

The authors acknowledge the personnel at the participating primary healthcare centres, and we would like to thank the patients participating in the study.

Ethical approval

The study was approved by the Regional Ethical Review board in Lund, 25 June 2015 (reference number 2015/396) and was registered in the EU Clinical Trials Register, number EudraCT 2015-001752-30. The study was conducted according to the ethical principles of the Declaration of Helsinki. All participants were informed of the study, both verbally and in writing, and provided written consents before participation. In the case of children, both the child and the guardian/guardians provided consent before participation.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

The study was funded by the Public Health Agency of Sweden. The Healthcare Committee, Region Västra Götaland, Sweden, partially funded the Region Västra Götaland part of the study.