July 9 (Bloomberg) -- Jalapeno peppers caused some cases of salmonella in the U.S., according to investigators who continue to examine whether tomatoes also could be a source of the worst foodborne outbreak in a decade.

At least 1,017 people in 41 states, the District of Columbia and Canada have become infected with the culprit Salmonella Saintpaul strain since mid-April, the Centers for Disease Control and Prevention said today on its Web site. That's an increase of 74 cases since July 4. Officials still don't know how the produce was tainted, or where it came from.

Out of three large groups of illnesses that have been intensely investigated, two were traced to a restaurant dish containing fresh jalapenos, and one was linked to an item with jalapenos and tomatoes, the CDC said. The findings suggest the threat isn't just raw tomatoes, which officials have been urging consumers to avoid for weeks.

``The accumulated data from all investigations indicate that jalapeno peppers caused some illnesses, but that they do not explain all illnesses,'' the Atlanta-based CDC said. ``Raw tomatoes, fresh serrano peppers, and fresh cilantro also remain under investigation.''

The Food and Drug Administration expanded its warning against tomatoes from certain locations to indicate that consumers at ``increased risk of severe infection'' shouldn't eat raw jalapeno or Serrano peppers either, the CDC said. Those at greatest risk include infants, the elderly and people with impaired immune systems.

Salsa, Guacamole

Consumers should be aware that tomatoes and peppers are often used in the preparation of salsa, guacamole, pico de gallo, tortilla fillings and other dishes, regulators said. While those foods often are served in Mexican restaurants, the CDC said the illnesses haven't been associated with a specific ethnic food.

The government's initial investigation didn't point to jalapenos as the source of illnesses, said Robert Tauxe, deputy director of the CDC's division of foodborne, bacterial and mycotic diseases, in a conference call with reporters today. Recent studies suggested a link to the outbreak, he said.

Tomatoes, the food initially identified by the CDC as the likely cause, remain a ``prime suspect'' because they are still being eaten more frequently by those who became ill than by those who didn't develop salmonella, he said.

Proportion Unspecified

Tauxe, who described the salmonella cases as the largest foodborne outbreak in at least a decade, said the CDC wasn't able to specify the proportion of cases attributed to one food versus another.

A nationwide study found those who became ill were likely to have eaten fresh jalapeno peppers and cilantro as well as tomatoes, the CDC said today. The items were often eaten together. Investigators don't know if the peppers associated with the illnesses were grown domestically or were imported, said David Acheson, the FDA's associate commissioner for foods, on the conference call.

The ``vast majority'' of tomatoes in national distribution when the outbreak began were from Florida and Mexico, the FDA has said. The outbreak is proving difficult to investigate because produce is difficult to trace to its source and some of the suspected foods often are eaten together, said Acheson.

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

At least 203 people have been hospitalized with salmonella poisoning. One elderly man in Texas has died, and salmonella may also have contributed to the death of a second Texas man who had cancer.

To contact the reporters on this story: Catherine Larkin in Washington at clarkin4@bloomberg.net; Justin Blum in Washington at jblum4@bloomberg.net.

Last Updated: July 9, 2008 18:31 EDT