FARMERS and food safety officials still have much to figure out about the recent spate of E. coli infections linked to raw spinach. So far, no particular stomachache has been traced to any particular farm irrigated by any particular river.

There is also no evidence so far that Natural Selection Foods, the huge shipper implicated in the outbreak that packages salad greens under more than two dozen brands, including Earthbound Farm, O Organic and the Farmer’s Market, failed to use proper handling methods.

Indeed, this epidemic, which has infected more than 100 people and resulted in at least one death, probably has little do with the folks who grow and package your greens. The detective trail ultimately leads back to a seemingly unrelated food industry — beef and dairy cattle.

First, some basic facts about this usually harmless bacterium: E. coli is abundant in the digestive systems of healthy cattle and humans, and if your potato salad happened to be carrying the average E. coli, the acid in your gut is usually enough to kill it.