OKLAHOMA CITY (AP) — The Oklahoma State Department of Health says it's helping investigate a nationwide salmonella outbreak that's linked to a stimulant-like plant called kratom.

Officials say a total of 91 people in 36 states, including four cases in Oklahoma, have been linked to the outbreak.

Health officials say the outbreak is associated with kratom, a plant native to Southeast Asia that's consumed for its stimulant effects and as an opioid substitute. It may be brewed in a tea, chewed, smoked or ingested in capsules.

Epidemiologists obtained kratom powder from a store in Tulsa where a person who later became ill reported making a purchase. Officials say the epidemiologists found outbreak-associated strains of salmonella in both samples.

Salmonella poisoning causes abdominal cramps, diarrhea and vomiting.