A dozen more people have been infected with salmonella that officials from the Centers for Disease Control and Prevention say is a result of ingesting tainted kratom products.

The latest addition since the first announcement Feb. 20 brings the total to 40 sickened people in 27 states. Nearly half of those sickened were hospitalized, and no one has died.

Kratom is an herbal supplement that can be smoked, sipped in tea, or taken as tablets. People who take it have said that it helps relieve chronic pain and depression, and it can work as a replacement for opioids. Some people take it for its stimulating effects.

The drug is legal in the U.S. and has not been scheduled by the Drug Enforcement Administration.

But the Food and Drug Administration has warned the public against taking it. The FDA also has issued reports about deaths associated with kratom, though supporters of keeping the drug legal for research purposes note that the death certificates often mention the possible involvement other drugs.

CDC has not found a common brand or supplier of kratom responsible for the salmonella infections. It detected salmonella in leftover kratom powder from people who had gotten sick in North Dakota and Utah, bought on the websites soapkorner.com and kratoma.com. Not all people who were sickened have admitted to taking kratom.

The FDA explained in a release that to arrive at their conclusions, health officials interviewed people about the foods they ate and other exposures they had before they became ill. Of the 24 people interviewed, 17 reported that they took kratom in the previous week. A CDC representative said that proportion was “much higher ... than would be expected for a healthy group of people.”

Health officials are collecting other kratom samples to test it for salmonella and say that the investigation is ongoing. The illness is a type of food poisoning that results in diarrhea, fever and stomach pain, and can be particularly dangerous for people who have weakened immune systems as a result of HIV or chemotherapy.

The CDC recommended people abstain from taking the drug "because the source of salmonella contamination has not been identified."