A new test can distinguish between respiratory infections caused by viruses and those caused by bacteria and other germs.
The test identifies the unique signatures of the immune system as it fights viruses.
"There's a very specific response we have to viruses, versus bacteria, versus other pathogens," said study co-author Dr. Geoffrey Ginsburg, a clinical genomics researcher at the Duke Institute for Genome Sciences and Policy in Durham, N.C.
If widely adopted, the test, described on Sept. 18 in the journal Science Translational Medicine, could help curb the overuse of antibiotics, the researchers said.
When people come into the doctor's office complaining of coughs, chest congestion and a fever, it can be tricky to sort out whether bacteria or a virus is the culprit. Doctors may try to guess based on symptom severity, or ask patients to come back later if symptoms don't resolve. But they also may simply prescribe antibiotics, on the reasoning that it can't hurt.
But those individual decisions have contributed to the rise of drug-resistant strains of bacteria, which killed 23,000 people last year, according to the Centers for Disease Control and Prevention. [6 Superbugs to Watch Out For]
Ideally, doctors would like to know immediately whether a patient has a viral infection, which doesn't benefit from antibiotic treatment, or a bacterial infection, which may require the drugs. While tests for specific viruses exist, those aren't useful for most respiratory infections.
Ginsburg's team wondered whether there was a more general way to discriminate between viral and bacterial infections. The team gave the influenza virus to 17 patients, and then looked at which genes were activated in their systems by detecting RNA circulating in their blood. (RNA is a chemical copy of the DNA of genes that are active.)
The researchers then used those gene signatures to see if they could identify infections in a group of 102 people. Some people in the group had confirmed bacterial infections, others had viral infections and the rest were healthy.
The team found that the body's response to the viral infection activated different genes than bacterial and other infections did.
The test identified about 90 percent of the people with viral infections, and wrongly flagged four people with bacterial infections and one healthy person.
The findings have incredibly significant implications, said Dr. Octavio Ramilo, an infectious-disease specialist at Nationwide Children's Hospital in Columbus, Ohio.
"Nobody wants to take risks, so the tendency is to overuse antibiotics," Ramilo told LiveScience.
Once doctors know for sure that someone's cough is viral, they will be less likely to overprescribe antibiotics, he said. The approach probably could be widened to include other conditions, such as pneumonia, which is often caused by a virus, Ramilo said.
And because it uses a common technique already used in diagnostic testing, the new method could be easily adopted in the clinic, Ramilo added.
Though the current test doesn't specifically identify bacterial infections, the team is doing late-stage development for a similar test for bacterial infections.
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