A multistate outbreak of E. coli O157 infections linked to romaine lettuce on Wendy's burgers has more than doubled since last week, according to an update from the Centers for Disease Control and Prevention.

The case count now stands at 84 and spans four states: Indiana (6), Michigan (53), Ohio (23), and Pennsylvania (2). That's up from last week's case tally of 37 from the same four states. Currently, at least 38 of the people sickened have been hospitalized. Eight of those people, all in Michigan, have developed a serious and potentially life-threatening type of kidney failure called hemolytic uremic syndrome (HUS), the CDC reports. No deaths have been reported. So far, the people sickened range in age from 5 to 94 years, with a median age of 24.

Because of reporting lags, the CDC warns that "the true number of sick people in this outbreak is likely higher than the number reported, and the outbreak may not be limited to the states with known illnesses."

As before, the prime suspect in the outbreak continues to be romaine lettuce that Wendy's used exclusively on burgers and sandwiches (The fast-food chain uses different leafy greens for its salads). The CDC notes that among 62 affected people who were interviewed, 52 (84 percent) said they had eaten at Wendy's in the week before getting sick.

Lethal lettuce

In a statement last week, Wendy's said it is fully cooperating with the CDC's investigation. "While the CDC has not yet confirmed a specific food as the source of that outbreak, we have taken the precaution of discarding and replacing the sandwich lettuce at some restaurants in that region," Wendy's said. "The lettuce that we use in our salads is different, and is not affected by this action. As a company, we are committed to upholding our high standards of food safety and quality."

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As Ars has reported, Escherichia coli O157:H7, produces Shiga toxin, which is toxic to cells and can shut down a cell's protein production. Shiga toxin can cause severe disease, including hemolytic uremic syndrome (HUS), which affects eight people in this outbreak. In HUS, the toxin gets into the blood and leads to the mechanical breakdown of red blood cells and acute kidney injury. While no deaths have been reported in this outbreak, HUS can be deadly, and E.coli­ outbreaks linked to tainted lettuces have been fatal before.

The CDC notes that "investigators are working to confirm whether romaine lettuce is the source of this outbreak, and whether romaine lettuce served at Wendy's restaurants was served or sold at other businesses." And the agency notes that it "is not advising that people avoid eating at Wendy's restaurants or that people stop eating romaine lettuce."

But, E. coli-tainted romaine would not be a surprising confirmation. The lettuce—and salad fixings generally—have been the source of a string of similar outbreaks in recent years. And though it's not always clear how exactly the gut-busting bacteria get to lettuces, the culprit is often manure contamination from livestock onto crop fields.

Shiga-toxin-producing E. coli are shed from the guts of animals, particularly cattle. In a traceback investigation of a 2018 E. coli outbreak involving contaminated romaine lettuce, investigators concluded that manure runoff from an upstream, high-density cattle farm of more than 100,000 cows tainted canal water that may have been used to irrigate lettuce crops. That 2018 outbreak sickened at least 210 people in 36 states, sending 96 to the hospital, causing kidney failure in 27, and killing five.