The U.S. Food and Drug Administration said on Tuesday it had approved a fast test for H5N1 bird flu that can show in less than an hour if people are infected.

The test, made by Sunnyvale, California-based Arbor Vita Corporation, should greatly speed up diagnosis and treatment of people infected with avian influenza, the FDA said. Most current tests take hours.

"This test is an important tool to help quickly identify emerging influenza A/H5N1 infections and reduce exposure to large populations," said Dr. Daniel Schultz, director of the FDA's Center for Devices and Radiological Health. "The clearance of this test represents a major step toward protecting the public from the threat of pandemic flu."

H5N1 mostly affects birds, but it occasionally infects people and is deadly when it does. The World Health Organization says 413 people have been infected and 256 have died in 15 countries since 2003.

Quick treatment with the drug Tamiflu can help save lives but usually people are not diagnosed right away.

"The test, called AVantage A/H5N1 Flu Test, detects influenza A/H5N1 in throat or nose swabs collected from patients who have flu-like symptoms," the FDA said in a statement.

"The test identifies in less than 40 minutes a specific protein (NS1) that indicates the presence of the influenza A/H5N1 virus subtype. Previous tests cleared by the FDA to detect this influenza A virus subtype can take three or four hours to produce results."

Experts fear H5N1 could mutate into a form that spreads easily from person to person. If it did, it would cause a pandemic that could kill millions and devastate economies. Governments are trying to prepare for such an epidemic by stockpiling drugs, vaccines and diagnostic tests.