Twelve people in five states have been infected with E. coli O26 in an outbreak linked to raw clover sprouts served at Jimmy John’s sandwich restaurants, according to the Centers for Disease Control and Prevention.

Iowa has reported five cases, Missouri three, Kansas two, while Arkansas and Wisconsin have each reported one person infected with the outbreak strain, the CDC said in an investigation report Wednesday.

Those sickened range in age from 9 to 49 years old. Median age is 25. All the victims are female. Two of the 12 have been hospitalized.

The CDC says the onset of their illnesses ranged from Dec. 25, 2011 to Jan. 15, 2012.

“Preliminary results of the epidemiologic and traceback investigations indicate eating raw clover sprouts at Jimmy John’s restaurants is the likely cause of this outbreak,” the CDC concluded in its report. 

Raw sprouts served on sandwiches at Jimmy John’s restaurants have been associated with multiple foodborne illness outbreaks in recent years.

In 2008, at least 19 E. coli O157:H7 cases were linked to alfalfa sprouts sold at Colorado Jimmy John’s restaurants. In 2009, 228 people became ill in Nebraska, Iowa, South Dakota and Kansas after eating  Salmonella-contaminated sprouts at several restaurants, including Jimmy John’s outlets.

In late 2010, a 16-state Salmonella outbreak that struck 94 people was linked, in part, to alfalfa and spicy sprouts served at Jimmy John’s restaurants, while a separate outbreak of Salmonella a month later, which sickened seven people in Oregon and Washington, was also tied to Jimmy John’s sandwiches. 

Following those outbreaks, the company announced it was switching from alfalfa sprouts to clover sprouts nationwide.

In this latest outbreak, there’s strong epidemiologic evidence tying the illnesses to the Jimmy John’s chain.

Among 11 of the ill people who gave information to investigators, 10  — or 91 percent  — reported eating at a Jimmy John’s restaurant in the week before they became sick. Among those 10, eight said they ate a sandwich containing sprouts and 9 reported eating a sandwich containing lettuce.

The ill people ate at nine different Jimmy John’s locations in four states, the CDC reported. 

A traceback investigation by the Food and Drug Administration (FDA) continues, but the CDC said preliminary evidence points to a common lot of clover seeds used to germinate the sprouts served at the Jimmy John’s outlets where the sick people ate. 

“FDA and states conducted a traceback that identified two separate sprouting facilities; both used the same lot of seed to grow clover sprouts served at these Jimmy John’s restaurant locations,” the report stated. “On February 10, 2012, the seed supplier initiated notification of sprouting facilities that received this lot of clover seed to stop using it. Investigations are ongoing to identify other locations that may have sold clover sprouts grown from this seed lot.”

At this time, the CDC said no other restaurants or grocery stores are associated with the outbreak.

PulseNet, the national surveillance system of foodborne illnesses, is being used to identify additional cases that might be part of the outbreak.

But the E. coli serotype in this latest outbreak is rare, and the genetic fingerprint pattern has never been seen before in PulseNet, the CDC said. The 026 serotype is among the so-called “Big Six” E. coli strains soon to be regulated in ground beef.

The CDC notes that because non-O157 E. coli strains are more difficult to identify than E. coli O157:H7, many clinical laboratories do not test stool specimens for them and therefore O26 infections may go undiagnosed and unreported.

When Jimmy John’s began serving raw clover sprouts a year ago, it did so saying it hoped to decrease the chances of contamination. Clover seeds are smoother than alfalfa seeds, and presumably easier to sanitize. 

Sprouts, which have been the cause of many foodborne epidemics, are considered a high-risk food because they have the potential to carry large amounts of pathogens. If the seeds used to germinate sprouts become contaminated with feces from domestic or wild animals – perhaps through contaminated water or improperly composted manure fertilizer – the  sprouts will also be contaminated. The warm, moist conditions used to grow sprouts permit harmful bacteria to rapidly multiply.

Citing food safety concerns, Walmart stopped carrying sprouts in its stores in October 2010. Last month, the national restaurant chain Jason’s Deli announced it would not serve sprouts for the remainder of 2012 and possibly 2013.

Since 2000, sprouts have been linked to 30 foodborne illness outbreaks in North America, Europe and Australia, including last spring’s outbreak of E. coli O104:H4 centered in Germany, which sickened 4,321 people and killed more than 50. That outbreak has been linked to sprouts grown from contaminated fenugreek seeds.

The continued use of raw sprouts in the face of multiple outbreaks has many baffled, including food safety attorney Bill Marler, publisher of Food Safety News. “As a business man I am left wondering why a company would continue to take this kind of financial and public relations risk,” Marler said in a news release. “As a food safety advocate I am concerned that customer safety is not being taken seriously.”

“When people think of sprouts, they think of a health food. They aren’t thinking about serious illness, hospitalization, or worse,” he said. “However, the track record for sprouts suggests that consumers ought to know the dangers. And, of course the onus for providing this information falls on those who are selling sprouts.”

Marler has suggested that sprout growers include a warning label on their product that alerts consumers to the risks associated with consuming raw sprouts.

CDC Outbreak Map:

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James Andrews contributed to this report.