HOUSTON -- Health officials on Tuesday urged Texans not to eat certain types of raw tomatoes as they investigate a nine-state outbreak of Salmonella, including 21 confirmed cases in Texas.

Half of those cases are out of Harris County.

No deaths have been reported in Texas since the outbreak began in mid-April.

Officials with the Texas Department of State Health Services said the investigation is in its early stages, but consumption of raw tomatoes has been targeted as the likely source of the Saintpaul strain of the Salmonella bacteria. Specific types and sources of tomatoes have not been identified.

As they work to determine the source, health officials are advising that people not eat any raw Roma or full-sized round tomatoes other than those sold attached to the vine or grown at home.

The confirmed cases of Salmonellosis were found in Harris, Fort Bend, Dallas, Tarrant, Hays and Cameron counties. Seven people in Texas had to be hospitalized.

“Normally Salmonella is a fairly mild infection with stomach cramps diarrhea, maybe nausea and vomiting for a few days,” said Emily Palmer, a spokeswoman for the Department of State Health Services. “But for some people it can be very serious ... that’s one of the reasons why we want to alert the public.”

In addition to 21 people in Texas, dozens more have become sick with the same infection in New Mexico, Arizona, Utah, Colorado, Kansas, Idaho, Illinois and Indiana.

More cases were reported Tuesday in Montana, Virginia and Wisconsin, Palmer said.

On average, about 30 cases of this particular strain of Salmonella are confirmed in Texas in a year.

No farm, distributor or grocery chain has been identified as the main source, but HEB has pulled their roma and salad tomatoes from the produce aisle.

Salmonella is a bacterial infection that lives in the intestinal tracts of humans and other animals. The bacteria are usually transmitted to humans by eating foods contaminated with animal feces.

According to the Centers for Disease Control and Prevention, most people infected with Salmonella develop diarrhea, fever and abdominal cramps 12 to 72 hours after infection. The illness usually lasts four to seven days, and most people recover without treatment.

In some cases, the diarrhea may be so severe that the patient needs to be hospitalized. The infection can spread from the intestines to the bloodstream, and then to other body sites and can cause death. Elderly people, infants, and those with impaired immune systems are more likely to have a severe illness.

Consumers also are advised to:

Cook tomatoes at 145 degrees for at least 15 seconds to kill Salmonella;

Avoid purchasing bruised or damaged tomatoes and discard any that appear spoiled;

Thoroughly wash all tomatoes under running water;

Refrigerate within two hours or discard cut, peeled or cooked tomatoes.