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Group A Streptococcus Infection and Influenza Get New Point-of-Care Tests

In an article published in Clinical Microbiology Newsletter, Jennifer Woo, MD, University of California, Los Angeles, and colleagues discuss the point-of-care (POC) diagnostic testing for group A Streptococcus (GAS) infection and influenza.

“Diseases caused by these 2 organisms represent many visits to primary care providers, urgent care clinics, and emergency departments,” the authors write.

Group A Streptococcus
GAS is the most common cause of bacterial pharyngitis. However, it is difficult to distinguish GAS pharyngitis from pharyngitis due to other infectious causes based on clinical symptoms alone. A rapid diagnostic assay to easily differentiate between these causes of pharyngitis can thus reduce inappropriate antibiotic use, while also improving patient satisfaction and clinic workflow.

Rapid antigen detection tests (RADTs) are POC tests used for GAS. However, although these tests have been shown to help guide clinical decision making and reduce unnecessary antibiotic prescriptions, they have low sensitivity in children. Because of this, clinical practice guidelines recommend that clinicians submit specimens for culture in cases with negative results by RADT. However, although culture is the gold standard test for GAS, it requires 24 to 72 hours to produce a result. Many clinicians are also unaware of the recommendations for culture in cases of a negative RADT result.

In Clinical Laboratory Improvement Amendments (CLIA)-waived outpatient settings, RADT has also been associated with high rates of false-positive results, typically because of improper test interpretation by inadequately trained laboratory personnel.

However, recently, the US Food and Drug Administration (FDA) “has granted CLIA waivers for 2 nucleic acid amplification-based POC tests for GAS,” the authors say. Although few studies have analyzed these tests, data so far suggest that both offer high (>93%) sensitivity and specificity compared to culture.

These improved tests may ultimately prevent the need for a backup culture of specimens found to be negative for GAS by current POC methods, the authors add.

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Influenza A (H3N2) has caused most of the illnesses in this severe flu season, but influenza B is becoming increasingly responsible for more infections as the flu season continues to hit the United States.