Overall, officials emphasized beef is safe if you heat it sufficiently on the grill. Nationally representative samples of beef, officials said, did not appear to show traces of the virus. Start the day smarter. Get all the news you need in your inbox each morning.

The findings, in which scientists injected high levels of an H5N1 bird flu virus surrogate into ground beef, indicate that properly cooking hamburgers to a temperature of about 145 to 160 degrees Fahrenheit (63 to 71 degrees Celsius) keeps them safe for consumers.

Laboratory tests by the US Department of Agriculture haven’t found any H5N1 bird flu virus in raw beef, but they are a good reminder why eating rare hamburgers can be risky.

Bird flu typically spreads among birds, but there have been recent outbreaks among cattle in the U.S., and one Texas man contracted the virus from sick cows. Here’s why so many experts are worried about a possible new pandemic.