Simple blood test distinguishes between viral, bacterial infections

A simple blood test that can diagnose an infection as bacterial or viral may improve care and address antibiotic overuse, say Stanford University School of Medicine researchers.

While antibiotics should only be used to treat bacterial infections, it is difficult for doctors to differentiate between bacterial and viral infections in their patients, researchers noted. Thus, doctors may overly rely on antibiotics as treatment, especially in critically ill patients.

“If you are looking for 12 different viruses, you must perform 12 different tests,” study senior author Dr. Purvesh Khatri, an assistant professor at Stanford University School of Medicine, told “It is very time consuming and very expensive.”

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According to the Centers for Disease Control and Prevention (CDC), drug-resistant bacteria cause over 2 million illnesses and 23,000 deaths each year, and as many as 50 percent of antibiotic prescriptions are unnecessary.

In a study published Wednesday in Science Translational Medicine, Stanford researchers used a blood test that observed seven human genes whose activity changes during infection, creating a pattern that can distinguish whether an infection is bacterial or viral. This gene expression is the process by which the body extracts information from a specific gene and uses it to direct protein formation in response to external stressors.

The test resulted in a 98.5 percent accurate diagnosis of the study’s 96 participants, all critically ill children.

“The test is surprisingly, highly accurate,” Khatri said.

He added that their work stemmed from the team’s previous research that documented a common immune reaction to viral infections, and whether it differed from reactions to bacterial infections. The team thus began to wonder if they could exploit those differences and use them to distinguish between bacterial and viral infections in hospital patients.  

Currently the test takes four to six hours to complete— a time researchers say is too long for critically ill patients, but developers hope the test will be incorporated into a device that will reduce the turnaround time to under an hour. Part of their plan for speeding up results includes pairing their seven-gene test with an existing 11-gene test, which reveals whether infection is present in a patient. The first of its kind, the 18-gene combination test will show if the patient has an infection and whether it is viral or bacterial.

The cost for the test is not yet known, but Khatri said researchers’ goal is for it to cost as much or less than antibiotics, incentivizing doctors to use the blood test over writing prescriptions.

“It’s very cheap to get an antibiotic, especially in developing countries,” Khatri said. “Any suspicion [of a bacterial infection] will get you an antibiotic, a fever will get you [an antibiotic] … [the test] would be cheap enough that it would be cost neutral.”

There are currently five to six clinical trials of different test populations ongoing at Stanford Medicine. Khatri anticipated that the device will be available in 2 to 3 years.

“This test will result in cost saving, in the health fields, for the long run, and remove [time and money] boundaries for physicians,” he said.