The fingerstick test, FebriDx, works by detecting myxovirus resistance protein A, which the body generates in response to viral infections, and C-reactive protein (CRP), which is associated with systemic bacterial or viral infection.
In a study of 520 adults and children with symptoms of acute respiratory illness who were treated in outpatient settings, the test correctly classified bacterial infections 93.2% of the time (95% confidence interval [CI], 84.9-97.0). The negative predictive value (NPV), or probability that a person with a negative test result was truly free of a bacterial infection, was 98.7% (95% CI, 96.9-99.4).
The findings of the study, which was sponsored by the test’s manufacturer, were published in JAMA Network Open).
The ability to rule out a bacterial cause “may provide clinicians with reassurance to withhold antibiotics when supported by the clinical assessment,” the researchers wrote.
They added that the ability to identify infections that may benefit from antibiotics and confidently rule out those that will not “is essential to optimizing clinical management and addressing global antimicrobial resistance.”
FDA concerned about false negative viral infection results
FebriDx has been cleared for sale in the United Kingdom, Europe, Canada, United Arab Emirates, Brazil, and Australia, according to the manufacturer, Australia-based Lumos Diagnostics.
However, the product is not available in the United States, where the Food and Drug Administration denied marketing clearance in July. In a news release, Lumos said the FDA determined that FebriDx did not demonstrate “substantial equivalence” to a predicate device and expressed concern that false negative viral infection results could lead to missed cases of COVID-19.
In the newly published study, FebriDx identified individuals with viral infections 70.3% of the time (95% CI, 64.8-75.2). The probability that a person who tested negative for a viral infection was truly negative was 66.7% (95%CI, 60.8-72.1).
The study included patients with respiratory symptoms and recent fever who were enrolled from October 2019 to April 2021 at nine emergency departments, six urgent care clinics, and five primary care clinics in the United States. All patients were tested with FebriDx and underwent separate laboratory testing to determine a final diagnosis.
In addition, researchers recruited a control group of 120 individuals without symptoms.
Among 496 symptomatic individuals who had a final diagnosis, 73 (14.7%) were classified as having a response associated with a bacterial infection, 296 (59.7%) as having a viral-associated response, and 127 (25.6%) as negative.
FebriDx correctly ruled out a bacterial infection 88.4% of the time (95% CI, 85.0-91.1). The probability that a patient with a positive result for bacterial infection actually had a bacterial infection was 58.1% (95%CI, 49.1-66.7).
The findings bolster those of a previous study on the same test. This research included 220 patients who reported having a fever within the prior 3 days or had a measurable fever at the time of enrollment. In that study, the test correctly identified bacterial infections 85% of the time and correctly ruled out bacterial infection 93% of the time, with a NPV of 97%.