Rapid Antigen Detection Testing for Group A Streptococcus as an Adjunct for Early Diagnosis of Necrotizing Soft Tissue Infection: A Case Series.

Necrotizing soft tissue infection (NSTI) is a rapidly progressive, life-threatening soft-tissue infection most commonly caused by group A Streptococcus (GAS). Although early diagnosis and prompt surgical intervention are crucial, the initial presentation is often nonspecific, which can occasionally delay diagnosis and surgical intervention. We report three cases of NSTI caused by GAS in which rapid antigen detection tests (RADTs), in conjunction with imaging and surgical exploration findings, were helpful in the diagnosis of NSTI: a 47-year-old man presented with left groin swelling and pain (Case 1); a 72-year-old man with right thigh erythema and tenderness (Case 2); and a 63-year-old man with right lower leg redness and pus discharge (Case 3). All three patients had elevated levels of inflammatory markers, and imaging revealed subcutaneous fat stranding. RADTs performed on the wound or tissue samples were positive in all cases prior to culture confirmation. Each patient underwent prompt surgical debridement combined with empirical broad-spectrum antibiotics. In Case 3, the Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score was a false negative, demonstrating the limitations of laboratory-based scoring in early NSTI. However, a positive RADT result, in conjunction with subcutaneous fat stranding observed on computed tomography scan, enabled timely surgical intervention. This study suggests that RADTs, when combined with clinical assessment and imaging, may serve as valuable adjuncts for early diagnosis and management of NSTI.