A shopper walks through the produce area of a Simi Valley, Calif., grocery store. The last month has seen a tidal change in the way Americans buy food.

The third disease outbreak from E.coli 0157:H7 linked to Romaine lettuce in the past year is raising questions what specifically about the crop may cause such problems.

While not much is yet know about the outbreak’s source, one theory is that Romaine’s upright, “baselike” structure could be collecting contaminants more readily, said Trevor Suslow, vice president of produce safety at the Produce Marketing Association.

“That’s not exclusive to Romaine, but it tends to have an upright growth habit,” he said.

Though Romaine lettuce shouldn’t be painted broadly as a more hazardous crop, the produce industry does want to identify any potential risk areas that can be mitigated, Suslow said.

The largest produce companies are already in compliance with preventive controls established by regulations for the Food Safety Modernization Act, which became law in 2011, he said.

However, produce companies have been adopting best practices regarding human hygiene, agricultural water quality and soil amendments such as manure since the mid-1990s, Suslow said.

“Some of this could be a function of Romaine being a highly consumed leafy green,” he said.

Though the crop’s popularity could play a role in the frequency of the recent outbreaks, iceberg lettuce is roughly just as commonly consumed but hasn’t experienced as many problems, said Scott Horsfall, CEO of the Leafy Greens Marketing Agreement, a commodity group aimed at improving food safety in the sector.

“It’s a problem we’re going to have to look at,” he said.

Horsfall said the theory regarding Romaine’s upright structure is not unreasonable, though the subject of the crop’s specific features will have to be explored more thoroughly.

“That’s what we’re trying to figure out,” he said.

The latest outbreak, which sickened 32 people in 11 states during October, has the “same DNA fingerprint” as the variety of E.coli 0157:H7 tied to an outbreak in late 2017, according to the Centers for Disease Control.

However, the recent outbreak doesn’t appear to be from the same strain that sickened more than 200 people and killed five in the spring of 2018, which was thought to be connected to contamination from a nearby feedlot in Yuma, Ariz.

The Romaine believed to have caused the most recent outbreak would likely not likely have come from that area, but from California’s “salad bowl” in the vicinity of Salinas, where the crop is generally grown in spring and summer, said Horsfall.

“The impact of this particular advisory will be felt very much in the desert, because that’s where the product is coming from now,” he said.

Horsfall said the industry was working with federal authorities to identify the outbreak’s source and communicating with the public.

“You can’t ignore the fact that when there’s an issue like this, there are real people getting hurt,” he said.

For the produce industry, there’s also an associated impact on consumer attitudes and trust, Horsfall said.

Historically, such outbreaks adversely affect growers beyond the crop that’s directly implicated, said Suslow. “It tends to have a ripple effect across the leafy green category.”