Group A Streptococcal Rapid Antigen Detection Test: A Clinical Study to Evaluate the Reproducibility Using Human Wound Samples.

Background: The early diagnosis of necrotizing soft tissue infection (NSTI) caused by group A streptococcus (GAS) for performing debridement surgery is key to the patient survival. In 1996, the diversional use of a GAS-rapid antigen detection test (RADT) for pharyngitis was reported, quickly spreading as a clinically useful method. However, no clinical study has evaluated the reliability of RADT by using wound samples. This is the first study using clinical wound samples to examine the reproducibility between GAS-RADT and wound culture.

Methods: Patients in whom wound culture samples were clinically necessary were included in this study. Two samples were obtained simultaneously: one for isolation of bacteria as wound culture and the other for GAS-RADT, with written informed consent. The reproducibility between GAS-RADT and wound culture was statistically evaluated by Cohen's kappa coefficient.

Results: One hundred samples from 94 patients were collected from 2020 to 2021. Two samples were GAS-positive on wound culture, and both were RADT-positive (positive reproducibility: 100%). Ninety-eight samples were GAS-negative on wound culture; of these, 97 were RADT-negative (negative reproducibility: 99%). Cohen's kappa coefficient was 0.80, indicating excellent agreement beyond chance. None of the bacteria showed cross-reactional influences. The only discrepant case (RADT-positive and wound culture-negative) was attributed to the administration of antibiotics for 2 days before the sampling.

Conclusions: The reproducibility between GAS-RADT and wound culture was statistically excellent, underscoring the reliability of GAS-RADT for wounds.