It's quite a departure from the 2006 E. coli outbreak in spinach, a mystery solved in about two weeks.
"We really, really got spoiled, if you will, with the spinach outbreak," Dr. Robert Tauxe, food safety chief at the Centers for Disease Control and Prevention, told The Associated Press.
There aren't as many spinach lovers as tomato lovers, and the spinach consumers remembered eating came in bags, often still left in their refrigerators, bearing bar codes that were as good a clue as a fingerprint in helping investigators race to the very field that had been contaminated.
This time around, the suspects seldom are left over in the refrigerator or bear individual bar codes. Also, the victims are having a harder time remembering.
They say, "'Well, I'm not sure, I may have had guacamole, or a garnish,"' Tauxe notes.
But this outbreak is lasting an unusually long time, with a record 1,017 cases confirmed by Wednesday -- the first of whom fell sick April 10 and the latest so far on June 26.
Tauxe said that makes the toll of the current salmonella outbreak far surpass recent large outbreaks of any foodborne disease: salmonella linked to peanut butter in 2006 and hepatitis A from green onions in 2003. It's not quite as big as when cyclospora-tainted raspberries sickened well over 1,000 people in the mid-1990s.
The scope is bad both for public health and a battered tomato industry that estimates losses at $100 million. Yet it is giving federal investigators some apparently valuable new clues.
Early on, lots of individuals got sick, not clusters of people who all ate at the same restaurant or catered picnic. But by mid-May and continuing well into last month, those clusters of five or more people sickened in the same spot were appearing. That's good news for disease detectives, who find it easier to trace suppliers for a few restaurants than hundreds of stores and market.
Plus, the CDC just finished comparing 144 people who got sick in June with 287 people who live near them but didn't fall ill.
That study of the June cases shows the sick are far more likely than the well to have eaten either raw tomatoes, raw jalapeno peppers or fresh cilantro. In one of the largest clusters, those sickened had consumed fresh tomatoes and fresh jalapenos mixed together. In two other large clusters, illnesses were linked only to a dish that contained fresh jalapenos but no tomatoes.
What does that mean?
"We are quite sure that neither tomatoes nor jalapenos explain the entire outbreak at this point. ... We're presuming that both of them have caused illness," Tauxe said.
That has the Food and Drug Administration looking furiously for intersections between peppers and tomatoes. Perhaps there are farms that grew tomatoes earlier in the spring and then switched to pepper harvesting, or distribution centers that handled both types of produce and contaminated incoming produce, said FDA's food safety chief, Dr. David Acheson.
The government's advice for now is to continue avoiding certain raw tomatoes -- red round, plum and Roma -- unless they were grown in areas cleared of suspicion.
People at highest risk of severe illness from salmonella should not eat raw jalapeno and serrano peppers, the CDC said Wednesday. The most vulnerable are the elderly, people with weak immune systems and infants. Serranos are on the list because they're hard to distinguish from jalapenos.
Did the CDC just miss a pepper connection early on?
"It's very hard for us to say that peppers were absolutely not part of the problem initially. They may have been part of the problem initially but not large enough to catch the attention of the investigations," Tauxe acknowledges.
But there are clusters of illness where jalapenos "simply were not on the menu," he added. "Likewise tomatoes have not disappeared," and more sick people than their healthy neighbors continue to report having eaten them.
The geography offers a potentially good clue too. Patients live in 41 states, Washington, D.C., and even Canada -- where three people got sick while traveling to the U.S. and a fourth case is under investigation. Most of the sick are in the Southwest, while parts of the Northwest have no cases and parts of the Southeast few.
"That begs the question is there something about the distribution of the product that contributes to that," Acheson said. "We've been trying to tease that apart."