While more people get diarrhea, fever, and abdominal cramps from eating salmonella-laced tomatoes, the FDA is still trying to hunt down the source of the outbreak.

Last week the FDA announced that it’s going to expand the search to investigate packing or shipping sites and communal water sources on farms. FDA officials are also checking out other veggies used to make salsa–like jalapeno peppers and cilantro–as possible outbreak suspects.

According to the CDC, salmonella are usually transmitted to humans by eating foods contaminated with animal feces. Food microbiologist, Keith Warriner, explained the science:

The bacteria probably come from groundwater contaminated with animal feces, he says. Once Salmonella gets on and into a tomato, the fruit acts like an incubator. Bacteria divide even in the cool temperatures of packing houses. ‘If you get a few samples into the internal tissue, then they will grow for sure.’

Fresh vegetables are increasingly packaged and shipped in centralized locations, so instead of a localized outbreak, we see a nationwide or even worldwide epidemic.

In 2007, about 125 billion pounds of cattle, broilers, hogs, and turkeys were produced in the U.S. As Vegan Bits says rather bluntly, “that’s a lot of poop to process!”

Much of that poop is recycled on our nation’s fields to feed the crops, including veggies. Without careful handling, poop used as fertilizer can contaminate irrigation water and even directly contaminate crops. Mexico denies its involvement, so perhaps we need to look at our own food system.

If you don’t know what to do with the tomatoes you’ve decided not to eat, read Tom’s suggestion over at Grist. Watch out, stomach, those red orbs can be dangerous.