Jalapeno peppers, and not tomatoes, caused some of the salmonella infections in what has become the largest food-borne disease outbreak in the past decade, federal officials said Wednesday.

But both produce items, along with raw serrano peppers and cilantro, are still under investigation as the outbreak continues and investigators scramble to find the source and shut it down.

On Wednesday, the Centers for Disease Control and Prevention called for anyone at higher risk of food-borne illness to avoid raw jalapeno and serrano peppers, spicy chiles used in popular Mexican foods like fresh salsa and sometimes in pico de gallo, guacamole and tacos. That warning joins one issued more than a month ago, to avoid certain types of raw tomatoes.

"We are clear that jalapeno peppers caused some of the illnesses," said Robert Tauxe, a CDC deputy director. "It is not clear that they explain all illnesses."

Those at higher risk of food-borne illness include infants, elderly persons and anyone with a weakened immune system from diseases such as cancer. Others who are concerned about salmonella infection and want to reduce their risk may also want to avoid hot peppers, according to the CDC consumer advisory.

The salmonella saintpaul outbreak, which began April 10 , now totals 1,017 cases spread across 41 states, the District of Columbia and Canada. Two deaths in Texas have been linked to it.

Investigators are presuming that both tomatoes and jalapenos have sickened Americans, Tauxe said.

Tomatoes were initially suspected, and federal officials continue to warn against eating round red tomatoes, plum or Roma tomatoes unless they're from growing regions cleared in the investigation. That approved list now includes virtually every state that is a major tomato producer.

Federal investigators are checking into possibilities that tomatoes and peppers could have been grown on the same farm and exposed to contaminated water or processing equipment, or picked up the same bacteria by passing through the same distribution facility, said David Acheson, associate commissioner for foods for the U.S. Food and Drug Administration.

The warning about peppers comes after investigators looking into three clusters of illnesses found that one group had gotten sick from a food containing raw tomatoes and jalapenos; the other two groups had eaten the raw peppers, but no tomatoes. Adding to the confusion, the CDC is also looking at reports of victims who ate tomatoes but no hot peppers.

The CDC is analyzing hundreds of studies of what people ate before becoming ill, as well as checking a number of Mexican restaurants linked to small clusters of illnesses.

FDA investigators have sampled hundreds of places where tomatoes could have picked up contamination and found no matches with the outbreak bacteria. Now they're starting that process with hot peppers.

"It's just been a spectacularly complicated and prolonged outbreak," Acheson said. "I don't have an explanation for it."