Continued from Tomatoes: Salmonella.

How do foods get contaminated with salmonella? Water is the most common source. Sometimes, says food safety expert Dr. Doug Powell, associate professor at Kansas State University, livestock-contaminated water is used for irrigation or to rinse tomatoes.

Birds also can be salmonella carriers, he says, “which can be problematic if they poop on a vegetable.”

How serious is salmonella? So far in the current outbreak, there have been no deaths and 189 hospitalizations. But some experts estimate that for each reported illness, another 20 people may have been stricken but have not come forward. Common symptoms include nausea, vomiting, fever, diarrhea and abdominal cramps, all of which can be potentially serious, even fatal, for children, seniors and those with weakened immune systems.

What should consumers do to stay safe? Avoid raw red plum, red Roma and round red tomatoes unless you are confident they were grown in one of the FDA’s “cleared” areas, listed on its Web site (fda.gov); safe choices include grape and cherry tomatoes and tomatoes with vines still attached.

Canned and processed tomatoes are also safe – as is salsa in jars. Many retailers and restaurants now provide information about the source of their fresh tomatoes. A good rule of thumb: “If you don’t know where it came from,” says FDA spokesman Mike Herndon, “don’t eat it.”