WASHINGTON – A recall of contaminated hamburger linked to possible E. coli bacteria illnesses among 22 people is being expanded to 19 million pounds of meat sold nationwide, the Agriculture Department said Friday.

“This action is being taken as a cautionary measure to ensure the protection of public health,” said Agriculture Secretary Ann Veneman. “Public health is our number one priority and it is our number one concern.”

The beef recall by ConAgra Beef Co. of Greeley, Colo., expands a previous recall at the end of last month.

The Agriculture Department and the Centers for Disease Control and Prevention said 16 people have been diagnosed with E. coli from the tainted meat in Colorado. Six other ill people in California, Michigan, South Dakota, Washington and Wyoming might be linked to the ConAgra meat, the agencies said.

The 19 million pounds of meat were produced between April 12 and July 11, officials said. Officials are still collecting details and expect to release later information that will allow consumers to identify products that should be returned to stores or discarded.

“This has just begun,” said Elsa Murano, the undersecretary for food safety. She said no E. coli has been found at the plant since July 11.

ConAgra is cooperating with the Agriculture Department, officials said. Veneman, asked if the department will cite the company for violations, said a government investigation at the plant is continuing.

The recall is the biggest since 1997, when Hudson Foods recalled 25 million pounds of ground beef after 15 people in Colorado fell ill from E. coli after eating hamburger from its Columbus, Neb., plant.

Two weeks ago, the company recalled 354,200 pounds of ground beef, nearly a month after a positive E. coli test at a Denver packing house raised the first sign of trouble.

The ConAgra recall follows another earlier this week by Carneco Foods LLC of Columbus, Neb., that involved 131,000 pounds of frozen ground beef patties also possibly contaminated with E. coli. The Carneco meat was sold through Sam’s Club warehouse stores around the country, including ones in Bangor, Augusta and Scarborough, Maine.

E. coli is a bacteria found in the intestinal tracts and feces of livestock.

If it contaminates meat, it can lead to digestive illnesses and possibly death in humans. Health officials have been urging consumers to cook their ground beef to 160 degrees in the center to completely kill the pathogen.

Agriculture officials said no one is currently hospitalized, although some people have been admitted and then released, they said.

Testing is under way in other states as public health officials tried to establish the scope of the outbreak.

The voluntary recall is of beef trim that is used to make ground beef, as well as fresh and frozen ground beef products that may be contaminated with E. coli 0157:H7, officials said.

Americans ate 69.5 pounds of beef per person in 2000, reflecting steady but modest increases since 1993, when consumption fell to 65.1 pounds, officials said.