Duke University researchers are working on an intriguing idea—a blood test to determine whether a respiratory infection is caused by a virus or bacteria.

If it is developed, the test could make prescribing treatment easier and more accurate. Nearly three-fourths of patients with acute respiratory illnesses are prescribed antibiotics even though their infections are usually viral, studies have found. There is no treatment for most viruses.

Antibiotics kill many of the body’s good bacteria and can cause side effects such as gastrointestinal problems. Overuse of antibiotics contributes to the growing global public-health problem of antibiotic-resistant infections as the drugs become less effective.

Like many family physicians, Theodore Ganiats often sees congested, coughing, aching, feverish patients who are desperate for an antibiotic to relieve their ills. The problem is, he can’t usually confirm their respiratory infections are bacterial. Often, they are viral.

“It’s often hard to get a person who doesn’t need an antibiotic to accept that,” said Dr. Ganiats, a family physician and professor at the University of Miami, in Florida. “A test to be able to know when an antibiotic is needed would be tremendously helpful.”

In research published last month, the Duke University researchers said their blood test can determine whether a respiratory illness is caused by a virus or bacteria. “This includes everything from a runny nose all the way down to pneumonia,” said Ephraim Tsalik, an assistant professor of medicine at Duke University Medical Center and the Durham VA Medical Center and lead author of the study.

The test currently is available only as a research tool with an eight- to 10-hour turnaround time. The researchers are exploring development opportunities including collaborating with two biotechnology companies in hopes of developing a one-hour blood test that can be used clinically. Such a test is at least two to three years away and would require Food and Drug Administration approval, Dr. Tsalik said.

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