American salad lovers are in the midst of a crisis. E. coli continues to give consumers of romaine lettuce horrible, bloody, and sometimes fatal cases of the runs, and the actual source of contamination is nowhere in sight. All that officials know is that infection with the nasty, toxin-spewing O157:H7 strain happened somewhere in Yuma, Arizona, and that it only affected romaine lettuce. It’s a tough break for the beloved green, but it’s actually not that surprising that it’s a common E. coli vector in the first place.

Before the current outbreak, romaine lettuce was known to have caused two other E. coli outbreaks, one in 2011, with 26 cases, and one in 2010, with 56 cases. It isn’t that romaine lettuce is naturally bacteria prone; it’s that, by its nature and the way that it’s grown and sold, the leafy green has many opportunities to get contaminated. The United States Food and Drug Administration’s Good Agricultural Practices is a set of guidelines meant to prevent contamination from happening in the first place, devised for the simple reason that veggies grow outside, in the dirt, and as such are subject to a multitude of potentially bacteria-laden external inputs, like fertilizer, animal poop, tainted water, and dirty human hands. These concerns apply to romaine lettuce, though a lot of its potential for infecting people are inherent not only to the way it’s grown but to the way that it’s treated and used post-harvest.

Hydroponic Vegetable
Pretty much any leafy green that's consumed raw is a potential vector for E. coli.

After harvest, romaine lettuce is often rinsed, cooled, washed, and sprayed with water, sometimes repeatedly, in order to keep it looking fresh. In addition to potentially exposing the produce to tainted water, doing so also opens it up to contact with all sorts of potentially dirty implements: refrigerators, hoses, spray heads, and so on. Often, it’s sold as whole heads, in bags; other times, it’s sold pre-chopped and prepackaged. All the steps of prepackaging create new situations for E. coli to take root.

But the most crucial factor affecting romaine’s ability to give people E. coli infections is the fact that we eat it raw. This is also an issue with other leafy greens and sprouts that don’t get much more than a rinse before they end up in our salad bowl: Sure enough, some of the major E. coli outbreaks in the past couple of years have been due to “leafy greens” (2017; researchers couldn’t pinpoint what type), alfalfa sprouts (2016), raw clover sprouts (2014), and a bunch of ready-to-eat salads (2013).

There’s not much you can do to a head of potentially tainted romaine lettuce other than throw it away. Washing, in theory, could remove some of the bacteria from the surface of the leaf, but as the U.S. Centers for Disease Control and Prevention warned in April, this particular strain of E. coli was going deeper into the leaf, where it couldn’t be washed away by water. When handling meat, which is more likely to be tainted with E. coli because the bacteria comes from animal digestive tracts, the CDC recommends cooking to a temperature of at least 145°F (62.6˚C) for beef and to 160°F (70˚C) for ground beef and pork. It doesn’t list any recommendations for cooking vegetables.

Even though very good recipes for grilled romaine exist, it’s not worth the risk right now: The official count as of May 2 is 121 cases, and that number is still growing. Until the end of Romainegate, the CDC says it’s best to avoid romaine unless you know for sure that it’s not from Yuma. Iceberg, anyone?