Rapid Diagnosis of Group A Streptococcal Septic Arthritis of the Knees in the Emergency Department Using Point-of-Care Gram Staining of the Synovial Fluid

Group A <i>Streptococcus</i> (<i>Streptococcus pyogenes</i>) infections are increasing globally and can be invasive despite immunocompetence. Septic arthritis requires an early diagnosis and prompt treatment. Because of its high specificity, Gram staining of the synovial fluid is crucial to early diagnoses; however, its sensitivity is low, and around-the-clock laboratory testing is often impractical. We report a case of oligoarticular septic arthritis in an immunocompetent man in his 60s. Point-of-care Gram staining of the synovial fluid revealed chains of Gram-positive cocci. An invasive streptococcal infection was suspected. Vancomycin was administered within 30 minutes of the left knee aspiration, as the patient was considered to be at increased risk for methicillin-resistant <i>Staphylococcus aureus</i> infection. Ceftriaxone was subsequently initiated after both knees were aspirated by the orthopedic surgeon, since beta-lactams are generally more effective than vancomycin against <i>Streptococcus</i>. After <i>S. pyogenes</i> was isolated from the blood and synovial fluid cultures, antimicrobial therapy was narrowed to penicillin G and clindamycin and was subsequently changed to ampicillin. Early diagnosis and treatment can improve the prognosis of such cases. Point-of-care Gram staining of the synovial fluid can play a crucial role in antimicrobial stewardship and improve the outcomes of patients with septic arthritis.