Group G Streptococcal Necrotizing Soft Tissue Infection: A Pitfall of Rapid Antigen Detection Test for Group A

Necrotizing soft tissue infection (NSTI) caused by group A Streptococcus (GAS) is well known to be associated with the rapid and frequent development and high rates of morbidity and mortality. Recently, the number of cases of NSTI caused by group G Streptococcus (GGS) and group C Streptococcus (GCS) infection has increased in many countries.¹ Bruun et al indicated that the fatality rate of GGS/GCG was 3 times higher than that in GAS infection.² Since 1996, the effectiveness of a rapid antigen detection test (RADT) for GAS for supporting the immediate diagnosis of GAS-induced NSTI has been reported as a diversional use^3,4, and its benefits and limitations in judging the need for early debridement surgeries have also been reported.⁵ This article reports 2 cases of lower extremity NSTI, in which the RADT for GAS was negative, where GGS infections were later detected.

Case 1

An 82-year-old woman was admitted to the hospital with a 4-hour rapidly spreading erythema and edema from the right ankle to the right lower leg. Her medical history included congestive heart failure with aortic valve replacement for aortic regurgitation, pacemaker implantation for sinus node dysfunction, stent treatment for angina, chronic renal failure due to nephrosclerosis, cerebral infarction, and total knee replacement of the right knee. Elevated body temperature (39.2°C) and tenderness out of proportion to the areas of erythema and edema area raised the suspicion of NSTI. A physical examination revealed the following: blood pressure, 166/67 mm Hg; pulse, 103 beats/min; O₂ saturation on room air, 98%. A blood test showed the following values: white blood cell, 7,680/μL; platelet, 108,000/μL; C-reactive protein, 3.6 mg/dL; creatine kinase, 219 U/L; creatinine, 3.9 mg/dL. A 1-cm skin incision on the medial side of the lower leg was made to observe the subcutaneous layer, and samples were taken for both a wound culture and an RADT for GAS; RapidTesta StrepA (Sekisui Medical Co., Ltd., Japan) (Figure 1, left). The result of the RADT was negative; however, tenderness that spread to the right inguinal region within 1 hour suggested the need for immediate debridement surgery under general anesthesia. As intraoperative findings, the “finger test” was positive and “dishwater” discharge was found (Figure 1, right). The removal of skin and subcutaneous tissue of the right lower leg and incision of the right thigh for drainage were performed. The need for broad antibiotic coverage led to the selection of meropenem and vancomycin as the initial antibiotic treatment. The wound culture from a small incision yielded GGS (Streptococcus dysgalactiae) without any other bacteria. Blood cultures on day 1 were GGS-positive. Additional debridement surgery on the right lower leg was performed on day 8 with application of negative pressure wound therapy (NPWT); V.A.C. Ulta (KCI, USA) (Figure 2, left). A split-layer mesh skin graft from the right groin was applied on day 15 of hospitalization (Figure 2, middle and right), and the patient was transferred to another hospital for rehabilitation on day 51 (Figure 3).

Case 2

An 84-year-old woman was admitted to the hospital with a 2-day history of fever and erythema of the left lower leg. Her medical history included chronic heart failure, hypertension, diabetes, dementia, and lymphedema of both lower extremities. She suffered severe tenderness with blisters in the left lower leg with an elevated body temperature (40.1°C). A physical examination revealed blood pressure, 131/66 mm Hg; pulse, 77 beats/min; O₂ saturation on room air, 93%. A blood test showed the following values: white blood cell, 15,930/μL; platelet, 195,000/μL; C-reactive protein, 36.7 mg/dL; creatine kinase, 57 U/L; hemoglobin A1c, 6.1%. A 1-cm skin incision on the lower leg was made to take samples (Figure 4, left). An RADT for GAS was negative; however, the rapidly progressing clinical course suggested the need for immediate debridement surgery under general anesthesia. Subcutaneous tissue was easily peeled off from the fascia with “dishwater” discharge (Figure 4, right). Antibiotic treatment was started by meropenem. GGS (Streptococcus dysgalactiae) was identified from a wound culture; however, blood cultures were negative. Successive treatment by additional debridement on day 8 with the application of NPWT (V.A.C. Ulta) and an operation using a split-layer mesh skin graft from her groin were applied on days 25 (Figure 5) and 57 of hospitalization, respectively. The patient was transferred to another hospital for rehabilitation on the day 77 (Figure 6).

The incidence of GGS-induced NSTI is increasing worldwide.^1,6 In Japan, the National institute of infectious diseases reported that the rates of NSTI caused by pyogenic I in 2014 were as follows: group A, 53%; group G, 28%; group B, 11%; and group C, 3%⁷. Komatsu et al analyzed the differences in clinical features between GAS- and GGS-induced cellulitis and reported that GGS-induced cellulitis occurred more frequently in older individuals with chronic underlying illness.⁸ Patients in this report were >80 years of age, and their medical histories included multiple conditions, including cardiac disorders and lower leg diseases.

A recent meta-analysis about GAS pharyngitis indicated high diagnostic accuracy of the GAS-RADT, with a sensitivity and specificity of 86% and 96%, respectively.⁹ The early diagnosis of NSTI is sometimes difficult because the initial physical signs are limited to tenderness, erythema, and fever.¹⁰ The RADT for GAS is effective for supporting the immediate diagnosis when judging the need for debridement surgery and selection of a narrower spectrum of antibiotics; however, surgeons should be aware of the limitations of this method. In both of these cases, a small incision was performed and samples taken for wound culture and a GAS-RADT. Although the RADTs were negative, immediate debridement surgery was performed because of the rapidly progressing clinical course in both cases. Clinical diagnosis is the most important gold standard for surgical decisions and management in progressing severe disease. The pitfall of using the GAS-RADT in NSTI screening must be recognized, and the appropriate initial treatment must be judged based on clinical examination and history of present illness.

This article reports 2 cases of GGS-induced NSTI in which the RADTs for GAS were negative, as an alert. Surgeons should be aware of the limitations and a pitfall of the GAS-RADT.

Affiliations: ¹Department of Plastic and Reconstructive Surgery, Graduate School of ­Medicine, Kyoto University, Kyoto, Japan; ²Department of Dermatology, Ijinkai Takeda General Hospital, Kyoto, Japan

Correspondence: Itaru Tsuge; itsuge@kuhp.kyoto-u.ac.jp

Disclosures: The authors have no relevant financial or non-financial interests to disclose.