Thirty-three people from five states were infected and nearly half of those were hospitalized in late 2012 after consuming spinach and bagged spring mix salads contaminated with E. coli.

The contaminated salads originated from a plant in Massachusetts.

There were nine outbreaks of foodborne illnesses in the U.S. last year, and one of five outbreaks associated with soil-grown produce, according to the U.S. Centers for Disease Control and Prevention (CDC). Preventive efforts are under way to reduce the occurrence of similar situations.

“If you’re going to grow products that will be consumed by humans you need to have a food safety program,” said JV Farms food safety director Fatima Corona.

“Food safety covers three types of contamination – physical, chemical, and biological. But the most severe would be biological because that could really make people sick.”

JV Farms manages about 8,000 acres in the Yuma area and produces a large portion of the lettuce crop grown there.

About 90 percent of the nation’s leafy green vegetables available during the winter come from Yuma, says Kurt Nolte, University of Arizona (UA) Yuma County Cooperative Extension director.

Microorganisms of greatest concern include Salmonella, Listeria, enterococci, norovirus, and pathogenic forms of Escherichia coli, commonly called E. coli, says Channah Rock, assistant professor and water quality specialist in the UA Department of Soil, Water and Environmental Science.

The Yuma County Cooperative Extension and the Department of Soil, Water and Environmental Science are part of the UA College of Agriculture and Life Sciences, and often coordinate efforts to assist with community and industry issues.

Rock’s graduate student Natalie Brassill is studying to detect E. coli most effectively in the water used to irrigate crops in three regions in California and southwestern Arizona.

Generic E. coli (E. coli that will not cause sickness) is commonly used as an indicator of water quality. Brassill’s project includes reviewing three Environmental Protection Agency (EPA)-approved methods for detection to figure out which method works best given different environmental conditions.

There can potentially be variations in the results of all three methods depending on the temperature or when there is higher salinity in the water, including after a local rain, Brassill says.

Each method can indicate the presence or absence of E. coli. Brassill is deciphering if and when these methods give a false indication of E. coli.

Growers periodically collect samples of irrigation water for lab testing of E. coli and other potential pathogens.

While no laws exist regarding levels of E. coli in irrigation water, the EPA’s legally unenforceable ‘guideline’ is the same as the one for bathing water. Bathing water must contain no more than 126 counts of E. coli per 100 milliliters of water – roughly equivalent to half a cup of water.

Irrigation water is one of many potential avenues how food can become contaminated. Produce must be protected at various points along the “farm to fork continuum,” Rock says.