Blood test can determine whether illness is caused by virus or bacteria

Researchers at Duke University say they have created a blood test that can determine whether a person's respiratory illness is caused by a bacterial infection or a virus, with over 90 percent accuracy.

What's more, the test only takes about 12 hours to get results. Current methods take several days to figure out whether a bacteria or a virus made a person sick, and they aren't always accurate.

Dr. Louis Weiss, professor of medicine and pathology at Albert Einstein College of Medicine, explained to CBSNews.com that the test has the potential to be extremely beneficial because it can help with diagnosis and prevent doctors from giving unnecessary antibiotics.

Antibiotics only work on bacterial infections and are useless against viral ones. Since both types of infections cause similar symptoms, it can be hard for doctors to determine which one is causing a patient's illness.

"A lot of times, you will give someone who is very sick or mildly sick antibiotics, and they will have a viral infection," Weiss, who was not involved in the study, explained. "This exerts a selective pressure on the environment as a whole and on all the bacteria that all of us carry."

Weiss said that a certain percentage of bacteria are naturally resistant to antibiotics. Once a treatment wipes all the other bacteria in the system, these "superbugs" continue to thrive and pass on their resistant genetic information to other bacteria. People then need stronger antibiotics to fight previously simple bacterial infections -- or, in the worst-case scenario, there may be no antibiotics left that offer protection.

The Centers for Disease Control and Prevention recently highlighted the growing problem of antibiotic resistance in a new report. They estimated that more than 2 million people suffer from drug-resistant infections annually, and 23,000 people die each year because of them.

Using antibiotics only when necessary can help stop the proliferation of superbugs. The new Duke University blood test could help do that by quickly identifying people with viral infections so they won't be prescribed antibiotics.

The test utilizes a genetic "signature" that a person's immune system gives off when something is attacking it. Viruses cause the immune system to turn on certain genes that remain dormant if a bacteria is infecting the host.

Before this test was developed, the Duke University team had completed research on volunteers who had been infected with various common upper respiratory viruses. They found about 30 genes that were affected by the immune response to a viral infection.

Duke University previously released a study on this genetic response in January. The research specifically looked at a blood test to help determine whether a person was infected with the H1N1 or H3N2 influenza virus.

At that time, the researchers said the genetic response could potentially be used to figure out the cause of any infection.

In the latest study, the Duke researchers tried the new blood test on patients who were arriving at their hospital's emergency room. A total of 102 people with fever symptoms were tested. Twenty-eight were determined to have a viral infection, 39 had a bacterial infection and 35 were designated as healthy controls. The test identified viral infections correctly in 89 percent of the cases, and accurately ruled out who was not having a viral infection in 94 percent of the cases.

The researchers hope that the blood test could also help identify illnesses caused by unknown emerging diseases, including potential bioterrorism threats.

"In instances such as pandemic flu or the corona-virus that has erupted in the Middle East, it's extremely important to diagnose a viral illness far more accurately and speedier than can be done using traditional diagnostics," senior author Dr. Geoffrey S. Ginsburg, director of Genomic Medicine and professor of medicine at Duke University School of Medicine, said in a press release. "Current tests require knowledge of the pathogen to confirm infection, because they are strain-specific. But our test could be used right away when a new, unknown pathogen emerges."

The study was published in Science Translational Medicine on Sept. 18.

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