(CBS)–An E.coli outbreak that has sickened nearly 150 people in 29 states so far is likely to worsen, according to an update Tuesday from the Centers for Disease Control and Prevention.

The outbreak—which has been linked to one death—has been traced to tainted romaine lettuce grown in Arizona’s Yuma Valley region.

CDC authorities advised consumers to avoid romaine lettuce unless it can be verified that it was not grown in the Yuma area. Growing season ended before the outbreak was reported, and the production of fresh romaine was halted several weeks ago.

Farmer John Boelts said growers and shippers adhere to the industry’s health and safety standards.

“Some of these things can be very difficult to identify—especially weeks and months after the fact,” Boelts said. “Folks in our business will work as closely with them as they’d like and try to get to the bottom of it.”

In an email to CBS, the Food and Drug Administration said packaging provides limited information about the source of the products.

The FDA and the CDC used new genome sequencing technology to link infections to the same potent strain of E.coli that was previously reported.

The CDC’s Deputy Chief for Outbreak Response, Matthew Wise, said the technology helps authorities trace cases of E.Coli back to their source.

“When we do the DNA fingerprinting, the intention of that is to try and connect different illnesses in different states together to say this actually something bigger that’s going on, and it’s not just a localized event,” Wise said.

Farmers in California reported a drop in romaine lettuce sales since the outbreak was reported.