U.S. researchers find 'signature' of common virus

* Test can distinguish between bacterial, viral infections

* Test can predict who will feel sick

By Maggie Fox, Health and Science Editor

WASHINGTON, Aug 6 (Reuters) - Common viruses that cause colds and flu leave a distinctive signature in the blood, and U.S. researchers said on Thursday they had found a way to pin it down.

The researchers hope to develop a test that will tell a doctor quickly whether a patient has a common cold, influenza or some other infection, and help guide treatment options.

"This work is still in a relatively early phase of discovery, but we are optimistic that these findings may lead to a whole new way of diagnosing infectious disease," Dr. Geoffrey Ginsburg of Duke University in North Carolina, who led the study, said in a statement.

Most respiratory infections look similar -- cough, sneezing, fever, headache and fatigue. There are no good quick tests and the U.S. Centers for Disease Control and Prevention published a study, also on Thursday, showing on-the-spot flu tests miss up to half of all flu infections. [ID:nN06348322].

Health experts say about half the time, a patient with a respiratory illness never learns what he or she had. It is also sometimes hard to predict who will become seriously ill.

"Until results are in, treatment is pretty much a best guess. Knowing exactly which pathogen is involved is important because it affects the urgency of response and the type of treatment," Ginsburg said.

Writing in the journal Cell Host & Microbe, Ginsburg and colleagues said they recruited 57 healthy volunteers who agreed to be inoculated with either a cold virus called a rhinovirus, respiratory syncytial virus or a seasonal influenza A virus strain.

The researchers tested each volunteer's blood, waited to see who became sick, and kept testing the blood. About half the patients in each group got sick.

They found a pattern of 30 genes that became active only among the patients who developed symptoms.

They also looked at studies of people with common bacterial infections such as Streptococcus pneumoniae and compared the genes active in those patients to the active genes in their virally infected patients.

They said their test could tell the difference.

The biggest value, they said, may be in helping doctors tell who has viral pneumonia and who has bacterial pneumonia. It is useless to treat viral infections with antibiotics.

"It could mean more appropriate use of antibiotics. Overuse of antibiotics can lead to the emergence of drug-resistant pathogens, and no one wants to see more of that," Dr. Christopher Woods of Duke said in a statement.

"This approach could lead to more precise, informed and tailored therapy -- essentially, personalized care for infectious disease," added Ginsburg.

The work is in early stages and more testing is needed, Ginsburg stressed.

The volunteers with influenza were treated with Roche AG's (ROG.VX) Tamiflu, an antiviral that helps reduce symptoms, the researchers noted.