Health officials have not nailed down the exact food involved, but the Centers for Disease Control and Prevention points the finger at an unnamed Mexican-style fast food chain it calls "Restaurant A."
That chain is Taco Bell, said William Keene, senior epidemiologist with Oregon Public Health.
"It's been clear for weeks that Taco Bell was the source for many of the illnesses," he said. "It's equally clear that it's not all Taco Bell. It's also not a single Taco Bell restaurant."
The first cases appeared at the beginning of April and continued through the third week in July. Dozens were sickened in Wisconsin, Indiana, Ohio and Kentucky, with a sprinkling of cases across the rest of the country. One person in Oregon -- a woman in her 20s in Klamath County -- got sick.
"It's very striking to have two such similar outbreaks at roughly the same time and both of them affecting Taco Bell," Keene said. "The similarities might be a coincidence."
Although no one food or menu item has been named a culprit, Keene said epidemiologists think that lettuce, tomatoes or both were to blame.
"It's not 100 percent sure it's one or the other but those are the chief suspects," he said. "We've been unable to tease them apart because everyone eats both."
Lettuce and tomatoes have been involved in a number of salmonella outbreaks in the past -- not because they're inherently risky -- but because they're popular food items that are often eaten raw. Proper cooking kills salmonella and other harmful bacteria.
Keene said the food involved in the outbreaks was clearly contaminated before reaching Taco Bell franchises.
"It's not something that they're doing wrong," he said. "One of the products that they using in their food was contaminated."
The Food and Drug Administration has been investigating the outbreak, trying to trace-back food from the restaurants to the source but lab tests have not turned up salmonella.
The strains -- Salmonella Hartford and Salmonella Baildon -- rarely cause food-borne illnesses in the United States. In fact, the last Baildon outbreak was in the winter of 1998-99 and also involved tomatoes.
In these current outbreaks, 80 people were sickened by Baildon, including the Klamath County woman, and 75 were infected by Hartford. No one died but about a third of the Hartford and about 40 percent of the Baildon cases were hospitalized, said Laura Gieraltowski, an epidemiologist at the CDC.
She said many of the cases involved women in their 40s, but it's not clear why.
"Taco Bell does not have a female bias in customers," Keene said. "They don't have any particular food items that are obviously women specific either."
The company did not return a phone call seeking comment.
CDC officials would not confirm that the company involved in the outbreaks was Taco Bell.
Naming a restaurant could have an economic impact on the company's bottom line, said Kristen Nordlund, an agency spokeswoman.
The outbreak is also considered to be over though both the FDA and CDC are continuing to investigate.
"There's no inherent reason for people to stop eating at Taco Bell now," Keene said.