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.

Influenza virus

Current recommendations for influenza treatment focus on early detection of infection and initiation of empirical treatment. This is especially true for high-risk individuals such as those aged 2 years and younger or 65 years and older, pregnant women, and immunocompromised patients. According to the authors, prompt diagnosis of influenza infection reduces the likelihood of hospital admission, length of hospital stay, duration of antimicrobial therapy, and the number of chest radiographs needed.

Rapid influenza diagnostic tests (RIDTs) are POC tests for influenza. They detect influenza A and/or B viral nucleoprotein antigens in respiratory tract specimens, by using immunoassay techniques, such as chromatographic lateral flow. These tests are CLIA-waived for use in outpatient settings and can help clinicians to screen for influenza.

RIDTs have high specificities (approximately 90% to 95%) and provide results quickly (typically within 15 minutes) and in a qualitative manner (positive versus negative). Nevertheless, the sensitivities of these tests for influenza A and B viruses are low, ranging from 50% to 70%.

However, novel rapid molecular tests have now emerged in influenza POC testing that detect viral RNA in upper respiratory tract specimens. These tests have promising (>90%) sensitivity and specificity for influenza A and B viruses and have potential to change the landscape of diagnostic testing, although they currently remain expensive, and their cost-effectiveness for influenza remains undetermined.

In summarizing, Dr. Woo and colleagues emphasize that “GAS and influenza virus diagnosis presents a clear clinical need for POC testing in certain clinical settings (urgent care clinics, primary care offices, and emergency departments).”

They stress that high-quality POC testing methods will continue to evolve, and will extend to pathogens beyond GAS and influenza virus.

“Hospital systems and ambulatory clinics can expect to see a continuous growth in POC testing. With the laboratory’s help, these new POC molecular tests can have a positive impact on patient care,” they conclude.

Dr. Parry graduated from the University of Liverpool, England in 1997 and is a board-certified veterinary pathologist. After 13 years working in academia, she founded Midwest Veterinary Pathology, LLC where she now works as a private consultant. She is passionate about veterinary education and serves on the Indiana Veterinary Medical Association’s Continuing Education Committee. She regularly writes continuing education articles for veterinary organizations and journals and has also served on the American College of Veterinary Pathologists’ Examination Committee and Education Committee.