The nationwide food poisoning outbreak from E. coli-tainted romaine lettuce has spread to 29 states and sickened 149 people, the Centers for Disease Control and Prevention said Wednesday.

That is an increase of 28 people and four states — Florida, Minnesota, North Dakota and Texas — since the most recent CDC update May 2. The number of people sickened in this outbreak has climbed steadily since federal authorities began investigating a month ago, making it the worst since the 2006 outbreak of E. coli illness from baby spinach, in which 205 people became ill and five died.

This strain of E. coli produces a toxin that causes vomiting and diarrhea and potentially other severe symptoms, including  kidney failure. Information was available on 129 of the people who were sickened. Of those — ranging in age from 1 to 88 — half have been hospitalized. Seventeen have developed severe kidney failure, and one person in California has died. About 65 percent of those sickened are women.

There is a time lag in reporting and confirming these cases, however. Officials may not yet be aware of people who have gotten sick in the last two or three weeks. The most recent illness reported started April 25.

California leads the nation with 30 cases, followed by Pennsylvania with 20 and Idaho with 11.

The outbreak has proved to be a complicated case for federal investigators. They have identified one farm in Yuma, Ariz., as having grown whole-head lettuce linked to cases of food poisoning in an Alaska prison, but they do not know where that lettuce became contaminated.

The rest of the cases involve chopped lettuce that did not come from that Yuma farm, according to the Food and Drug Administration. Many of the people sickened across the country ate chopped lettuce that had been sold in bagged form to restaurants. The bacteria could have contaminated the lettuce at any point in the production process.

“We still continue to go full-bore in trying to identify the source, not only the source of the contamination but also how the contamination actually happened,” Stephen Ostroff, FDA deputy commissioner for foods and veterinary medicine, told The Washington Post.

The CDC is still urging consumers to avoid eating or buying any kind of romaine lettuce from the Yuma region. That region grows the overwhelming majority of the lettuce and other leafy greens consumed in the United States in the winter months through early April. The lettuce season then shifts to California's Central Valley and Salinas Valley. Lettuce from California is not implicated in the outbreak.

Joel Achenbach contributed to this report.

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