Prepackaged iceberg lettuce from California has been linked to two separate outbreaks of E. coli that sickened more than 150 Taco Bell and Taco John’s customers late last year on the East Coast and in the Midwest, the U.S. Food and Drug Administration said Friday.

The news comes just months after officials fingered California spinach in an outbreak of E. coli O157:H7 that sickened more than 200 people and killed three.

It deals another blow to California’s leafy green industry, which dominates the nation’s supply. The iceberg lettuce industry alone had about $750 million in annual sales in 2005 – nearly 75 percent of the nation’s crop. Most of it was grown in the Greater Salinas and Central valleys.

“It just adds more fuel to the fire of the need to address this,” said Dr. David Acheson, chief medical officer for the FDA’s food safety center.

The recent outbreaks apparently have vindicated concerns he voiced last September, when he unenthusiastically announced his agency’s decision to lift a warning against eating fresh bagged spinach from California’s Central Coast. He pointedly noted at the time that of the 20 E. coli outbreaks from lettuce and spinach since 1995, nine were linked to the Greater Salinas Valley.

“Until some fundamental fixes are put in place in the areas where this contamination is happening,” Acheson said during a conference call with reporters, “there is obviously a concern that two months from now we’ll be having the same conversation, talking about outbreak No. 21.”

And, indeed, outbreaks No. 21 and 22 occurred about two months later. People began falling sick after eating at the fast food chains Taco Bell and Taco John’s in November. In the Taco Bell outbreak, which involved restaurants in New Jersey, New York, Pennsylvania and Delaware, 71 fell ill and 53 were hospitalized. The Taco John’s outbreak involved three eateries in Minnesota and Iowa. Eighty-one were sickened, including 26 who were hospitalized.

Outbreaks 21 and 22 also showed that the leafy green industry’s problems in California extend beyond the Greater Salinas Valley, where the tainted spinach was grown.

Taco Bell’s tainted lettuce was traced, via packaging, to farms in the Central Valley, although no specific sources have been named. The Taco John’s produce was traced both to the Central Valley and to the coast south of Salinas.

As with the spinach outbreak, investigators suspect that the initial point of lettuce contamination occurred at the farms, not in processing or distribution, said Jack Guzewich, director of emergency coordination and response for the FDA’s food safety center.

One likely problem is the proximity of ranching and farming operations in parts of California. Cattle and other animals harbor the bacteria, which is shed in their feces.

Supporting that theory, Acheson said officials found the same sub-strain of E. coli involved in the Taco John’s outbreak in two unidentified “environmental samples” from a dairy adjacent to one of the chain’s lettuce growers.

The implicated spinach was ultimately traced to four farms in Monterey and San Benito counties. Near one of the farms, which was next to a cattle ranch, officials found the sub-strain that caused illnesses in cow manure, a wild pig’s intestines and creek water.

The three successive outbreaks, all of which have run their course, also raise questions about what is causing them to occur with such frequency, said Trevor Suslow, a University of California, Davis, food pathologist.

“The fact that it seems to be happening even more frequently, in a more compressed time frame, one would have to speculate something is either being missed or something has changed to elevate the level of risk or potential of contamination,” Suslow said.