Don’t blame the lettuce! According to the Food and Drug Administration, the large E. coli outbreak which has just happened, caused by contaminated romaine lettuce, may have been caused by a factory farm.

A factory farm is a farm where the animals are crowded together in large numbers. Conditions are often abusive, and as we’ve seen from shocking videos, sometimes deliberately cruel.

E. coli bacteria live in the environment, animals’ intestines and in fecal matter, according to the Centers for Disease Control and Prevention. Dangerous strains of E. coli, as well as salmonella and other foodborne pathogens, are derived from animal (and occasionally human) feces, and can end up in the ground water, streams and rivers. “The bacteria in animal waste could make their way into water one of two ways,” explained University of Florida food safety expert Keith Schneider. “Water can run downhill, especially after rain, and make it into an irrigation ditch, or water can seep into an underground aquifer.”

A likely reason for why romaine lettuce is susceptible to E. coli contamination is that the runoff from cattle reaches the irrigation water for fields where romaine lettuce grows, said Benjamin Chapman, an associate professor and a food safety specialist at N.C. State University in Raleigh. In similar outbreaks in the past, contaminated produce was traced back to neighboring livestock operations. In this case, the FDA surmises that the contaminated water was either used to irrigate the lettuce or mixed with pesticides (a common method of dilution) before being sprayed on the plants.

These kinds of outbreaks have been happening again and again. Not all the harm from animal agriculture is done by meat itself. Sometimes it’s right next door!