i Rapid antigen detection tests (RADTs) for group A streptococci (GAS) are widely used for diagnosing acute pharyngitis, which has led to a considerable reduction in antibiotic prescriptions over the past decade. Beyond this intended use, their reassessment on invasive samples may be relevant in the management of life-threatening GAS infections. To this end, we evaluated the performances of three RADTs, culture, GAS PCR, and 16S rRNA gene PCR assays, and compared them with a composite gold standard (GAS-PCR assay and/or culture) for the diagnosis of severe GAS infection. A total of 192 specimens from deep-tissue (mostly normally sterile) sites enriched for 75 GAS-positive samples were enrolled in the study. The three evaluated RADTs showed sensitivities ranging from 88.0% to 94.7% versus 98.7% for GAS PCR, 84% for 16S rRNA gene PCR, and 77.3% for culture. The sensitivities of the ImmunoCard STAT! Strep A test (Meridian Bioscience) and the NADAL Strep A strip (Nal Von Minden) were similar to that of GAS PCR (P ؍ 0.25 and 0.03, respectively) and higher than that of culture (P ؍ 0.001 and 0.006, respectively), whereas the SD Bioline Strep A test strip (Standard Diagnostics) showed a performance similar to that of culture (P ؍ 0.02). The three RADTs detected 10 distinct emm types, including a predominance of emm 1 (33.3%), emm 89 (10.6%), and emm 12 (7.6%). No false-positive results were observed, leading to a specificity of 100% for all the evaluated RADTs. The GAS RADTs turned out to be sensitive, specific, and easy-to-use tools that may aid in the management of invasive GAS infections in 24/7 point-of-care laboratories by enabling early diagnosis and focused therapy.
Group A streptococci (GAS) are common bacterial pathogens responsible for mild diseases, such as pharyngitis, and invasive and life-threatening infections resulting from their dissemination into deep tissues. The worrying increase in the prevalence of these severe infections and their high fatality rates emphasize the need for rapid diagnostic tests to aid in patient management (1, 2).Over the past 2 decades, manufacturers have developed immunochromatographic rapid antigen detection tests (RADTs) that detect the polysaccharide C cell-wall antigen of bacteria. These tests are now widely used for diagnosing pharyngitis in pediatric outpatient clinics and private practices, which has considerably reduced the number of antibiotic prescriptions and resulted in fewer throat cultures performed by laboratories (3-5).Extending their indication beyond this intended use, namely, on deep-seated samples, may reduce delays in the diagnosis of invasive infections. To this end, we evaluated the performances of three commercially available RADTs approved for pharyngitis in the diagnosis of invasive GAS infections and compared them with those of conventional culture and molecular techniques.
MATERIALS AND METHODSPatients and clinical specimens. This survey was conducted by three teaching hospitals (in Lyon, Grenoble, and Saint-Etienne, France) between May 2013 a...