A multistate alfalfa sprout outbreak has sickened 55 people in 15 states, and Colorado is not one of them, the CDC says.

A food poisoning outbreak linked to alfalfa sprouts has sickened 55 people across 15 states, according to the Centers for Disease Control and Prevention, but Colorado is not among the states where illnesses have turned up.

The CDC said Friday it is tracking cases in Florida, Indiana, Iowa, Kansas, Michigan, Minnesota, New Hampshire, New York, North Carolina, North Dakota, Pennsylvania, South Carolina, South Dakota, Washington and Wisconsin. Four people have been hospitalized. State health departments in Minnesota and Wisconsin first flagged the outbreak earlier in the week after documenting more than three dozen cases between them.

Colorado health officials have not reported any illnesses connected to the outbreak, and the state does not appear on the CDC's list of affected locations. Sprouts distributed nationally can move through supply chains that touch multiple states even when no illnesses are confirmed in a given market. Some grocers and restaurants outside the identified states have still pulled the product or reviewed their sourcing while the investigation continues.

The outbreak involves two different pathogens. Investigators have identified both salmonella and Shiga toxin-producing E. coli, known as STEC, among the people who got sick. Most foodborne illness outbreaks are traced to a single pathogen, so the presence of two separate germs tied to the same food source has prompted the FDA and CDC to look closely at how the contamination occurred.

STEC infections can cause severe stomach cramps and bloody diarrhea, and in some cases lead to a kidney complication called hemolytic uremic syndrome, which is more common in children and can require hospitalization. Salmonella causes diarrhea, fever, vomiting and dehydration that typically resolve within a week but can be serious for young children, older adults and people with weakened immune systems.

Of 34 sick people interviewed by investigators, 26 said they had eaten alfalfa sprouts before falling ill, according to the Food and Drug Administration. That response rate led the FDA to focus on sprouts grown by Everything Sprouts, a Minnesota company that sells its product under the Calco and Everything Sprouts brand names to restaurants and grocery stores. The company has not issued a recall as of the CDC's latest update, and the FDA said it is continuing to work with the grower.

The FDA sent Everything Sprouts a warning letter last year after inspectors documented several problems at the facility, including a leaking roof that dripped water onto bean sprouts and onto workers' smocks during production. The letter followed inspections conducted the previous year.

Alfalfa sprouts have been linked to foodborne illness outbreaks before. The seeds are grown in warm, humid conditions that can also favor bacterial growth, and unlike many vegetables, sprouts are typically eaten raw, without any cooking step that would kill off contamination. The FDA and CDC have long advised people with weakened immune systems, young children, older adults and pregnant women to avoid raw sprouts of any kind.

For Denver-area shoppers, the immediate risk from this specific outbreak appears limited, since Colorado has not turned up in case counts and there is no indication so far that Everything Sprouts products are distributed in the Denver market. Sprouts sold at local grocery stores and used on sandwiches and salads at restaurants can come from a range of growers, and consumers who want to avoid any risk can check product labels or ask restaurants about their sprout supplier.

The CDC and FDA say the investigation is ongoing, and case counts could change as more states report illnesses or as health officials interview additional patients. Neither agency has said when the investigation might conclude or whether Everything Sprouts will issue a recall.