Consumer Reports interviewed Prof. Keith Warriner, Department of Food Science, about why there have been so many recalls of Californian-grown romaine lettuce .

Warriner, who studies foodborne illness linked to produce, says a major problem is lettuce farms located too close to large cattle farms known as CAFOs, or concentrated animal feeding operations.

Manure from these farms tainted with E. coli can be washed away by rain, contaminating lettuce irrigation water sources. Romaine leaves are delicate and can damage easily, he added, allowing bacteria to enter.

Warriner researches enhanced food safety in meat processing as well as produce. His team has helped advance knowledge in emerging pathogens, food-borne hazards detection technologies and intervention technologies.