Spinach found in the refrigerator of a person sickened by E. coli was contaminated with the bacteria, the "smoking gun" that investigators have sought for the origin of the deadly outbreak, health officials say.

Federal and state investigators on Wednesday focused their hunt to nine farms in California's greater Salinas Valley, said Dr. Mark Horton, the state public health officer. They also were checking processing plants, said Horton, who called the bag of tainted Dole baby spinach the "smoking gun" in the case.

Despite closing in on the source of the bacteria as likely somewhere in Monterey, San Benito or Santa Clara counties, officials continued to recommend that consumers not eat fresh spinach.

"Yesterday we had it down to California. Today we've got it down to three counties," said Dr. David Acheson of the Food and Drug Administration's Center for Food Safety and Applied Nutrition. "We want it down to a salad bowl and eventually a spinach leaf."

The tainted bag came from a refrigerator in New Mexico, said Department of Health officials for that state. A person who ate some of the leafy greens became one of 146 people in 23 states sickened by the outbreak. One person has died.

The spinach tested positive for the same strain of E. coli linked to the outbreak, Acheson said. Dole is one of the brands of spinach recalled Friday by Natural Selection Foods LLC, of San Juan Bautista, Calif.

The tainted greens — conventionally grown spinach and not organic — came from one of the farms that supplies spinach to Natural Selection, said Samantha Cabaluna, spokeswoman for Natural Selection.

Other bags of fresh spinach recovered elsewhere in the country also were being tested in the investigation.

"It's certainly premature to say only this bag is going to test positive," Acheson said. "There are others in the works."

Government and industry officials were working on how to allow spinach grown elsewhere back on the market, Acheson said.

Democratic Sens. Robert Menendez and Frank R. Lautenberg, both of New Jersey, pushed the FDA to assure the public spinach grown in their state is safe.

"As the nation's fourth-largest spinach producer, spinach farming is a multimillion-dollar industry for the Garden State," Menendez said. "That is why we are imploring the FDA to move quickly in identifying the source of the infected spinach."

Investigators began visiting farms in the Salinas Valley on Tuesday, seeking signs of past flooding or cases in which contaminated surface areas had come into contact with crops. They also were looking for potential sources of bacteria inside packing plants.

California produces 74 percent of the nation's fresh spinach crop. The Salinas Valley accounts for roughly three-quarters of the state's share, and it has been the focus of the investigation. The area has links to both Natural Selection Foods and a second company that's also recalled fresh spinach products, River Ranch Fresh Foods of Salinas.

A third company, RLB Food Distributors of West Caldwell, N.J., has has recalled Balducci's and FreshPro brand spinach products distributed to East Coast states because some of the spinach could have come from Natural Selection Foods.

Arizona and Colorado on Wednesday joined the list of states reporting E. coli cases. The others are California, Connecticut, Idaho, Illinois, Indiana, Kentucky, Maine, Michigan, Minnesota, Nebraska, New Mexico, Nevada, New York, Ohio, Oregon, Pennsylvania, Utah, Virginia, Washington, Wisconsin and Wyoming. Wisconsin has reported the most cases, as well as the lone death.

Among those sickened, 71 percent were women. Among those victims who could provide a date, they reported falling sick between Aug. 19 and Sept. 5, according to the Centers for Disease Control and Prevention.

New Mexico's public health laboratory isolated E. coli from the bag of opened spinach and then completed "DNA fingerprinting" tests late Tuesday. State and federal officials then matched it to the strain of the bacteria — E. coli O157:H7 — implicated in the outbreak.