(CNN) - An outbreak of 28 salmonella infections in 20 states has been linked to kratom products, the US Centers for Disease Control and Prevention said in a statement Tuesday. Though no deaths have been reported, 11 people have been hospitalized.
Native to Malaysia, the leaves of the kratom plant are traditionally crushed and made into tea to treat pain, though it is also chewed, smoked or ingested in capsules. In the United States, kratom products are sold as powders, pills, capsules and even energy drinks. Kratom is also called Thang, Kakuam, Thom, Ketom and Biak.
California had the highest number of salmonella cases (three). North Carolina, Ohio, Oklahoma, Oregon, Pennsylvania and Utah each reported two cases while Alabama, Arizona, Colorado, Florida, Kansas, Kentucky, Louisiana, Massachusetts, Michigan, North Dakota, New York, South Carolina and Tennessee each reported a single case, the CDC found.
Kratom should not be consumed in any form, the CDC said, because the source of salmonella contamination has not been identified.
People more likely to get a severe salmonella infection include pregnant women, young children, older adults and people with weakened immune systems, such as patients receiving chemotherapy. Most people infected with salmonella develop symptoms -- including diarrhea, fever and abdominal cramps -- within 12 to 72 hours of exposure to the bacteria.
Salmonella is usually transmitted when people eat foods contaminated with animal feces that carry the bacteria. Person-to-person transmission can occur if an uninfected person comes into direct contact with another person. An estimated 1.4 million cases occur in the US each year, according to the CDC.
Of the 11 people who have been interviewed for the salmonella investigation, eight reported consuming kratom in pills, powder or tea. Patients first reported feeling sick October 13, but the most recently reported illness began on January 30. Due to the reporting time lag, more cases of illness may be reported, the CDC said.
No common brands or suppliers have been uncovered by the investigation, which is being conducted by the CDC along with several state health officials and the US Food and Drug Administration.
Kratom products are very loosely regulated by the FDA.
FDA Commissioner Dr. Scott Gottlieb warned the public about the herbal supplement in a statement this month, saying that "There is no evidence to indicate that kratom is safe or effective for any medical use." Gottlieb likened the chemical compounds of kratom to opioids. Some scientists have challenged the FDA's description of kratom as too broad. All agree that more research is needed.
In addition to alleviating pain, kratom is consumed for its stimulant effects and used to treat heroin or morphine dependence, as it is said to reduce withdrawal cravings. Kratom has found a following in the United States, where there are 3 million to 5 million users, according to the American Kratom Association. The supplement can be found in head shops and gas stations.
The investigation is ongoing, the CDC said.
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