(CNN) Alfalfa sprouts are the likely source of a multistate salmonella outbreak that has caused 13 people to become ill, the Centers for Disease Control and Prevention said Tuesday.
The states where illnesses have occurred are Kansas, Missouri, Oklahoma and Pennsylvania.
No deaths have occurred in this outbreak, but five of the sick people have been hospitalized.
The earliest symptoms of illness began on December 1. Those who are ill range in age from 18 to 73 years.
Illness begins between 12 and 72 hours after exposure to the salmonella bacteria. Symptoms include diarrhea, fever and abdominal cramps and last four to seven days.
Local and state health officials in the affected states have been working with federal officials to identify the source of the outbreak, which they believe to be alfalfa sprouts produced by Inman, Kansas-based Sweetwater Farms. "Laboratory testing isolated salmonella from samples of irrigation water and alfalfa sprouts collected during a recent inspection at Sweetwater Farms," the CDC website said.
In interviews conducted by health officials as part of the outbreak investigation, ill people who reported consuming alfalfa sprouts did so at restaurants. One of the 12 interviews said sprouts were purchased at a grocery store.
According to the outbreak announcement from the CDC, Sweetwater Farms supplied the sprouts to five restaurant locations where sick people had eaten.
Health officials warned it is not safe to consume alfalfa sprouts from Sweetwater Farms.
CNN contacted Sweetwater Farms for comment but has not heard back.
Salmonella is responsible for 1 million cases of foodborne illness in the United States annually, including 19,000 hospitalizations and 380 deaths.