Fecal matter from humans, deer, sheep, goats, and insects may carry E. coli.

Salmonella also comes from fecal matter. “We have more than 2,000 types of Salmonella,” Masabni said, “and again very few affect people.”

Salmonella may be found in fecal matter from people, rodents, fowl, insects and snakes.

Shigella is a bacteria “more common in restaurants than in produce. It causes the third most common foodborne illness.”

“Listeria occurs in the soil, not fecal matter,” Masabni said. It can be deadly. “Mortality rate with Listeria is about 20 percent compared to 4 percent with Salmonella. It doesn’t multiply rapidly in the soil but can stay in pond water for 60 days or more.”

Raw manure is often a culprit in contaminating produce. “Pathogens have been found to survive in raw manure for one year, so it’s best not to use manure on produce. Keep fresh manure away from produce.”

Feedlots surrounded by crop land could also be cause for concern. Manure could move by wind or heavy rain into the nearby produce fields.

Masabni said properly composted manure reduces potential for contamination. In a publication on organic production he addresses using manure in vegetables.