A new study revealed tempeh was the source of a salmonella outbreak in 2012 that sickened 89 people. The Centers for Disease Control and Prevention linked a tainted batch of tempeh to the outbreak in North Carolina.

Tempeh is a popular vegetarian substitute for meat and is made from fermented and cooked soybeans. According to the New York Times’ Well Blog, the tempeh was unpasteurized and the Rhizopus oligosporus starter culture from Indonesia was the source of the contamination. At the time of the outbreak, the tempeh manufacturer, Smiling Hara, from Asheville, N.C., had voluntarily recalled the product.

The Salmonella outbreak started in North Carolina and spread to five other states between Feb. 29, 2012 and May 8, 2012. Of the infected, 81 lived in North Carolina. According to the CDC, the standard reporting form did not include meat substitutes as an item of interest, contaminated meat, poultry or raw vegatables are usually the focal point of salmonella outbreaks, but the individuals did state they ate vegetarian cuisine. A CDC survey of the first 50 patients revealed the possible source of contamination to be tempeh.

After visits to three restaurants in Buncombe County by the CDC, and further testing and site visits in other states, the government determined cross-contamination was at the heart of the outbreak. Many treated the unpasteurized tempeh as another ingredient and did not wash the cutting board after use or washing one’s hands after handling the product. The CDC reports states, “The role of cross-contamination in foodborne outbreaks is well established. Bacteria can be transferred from surfaces to food products hours after surface contamination. Ready To Eat foods typically do not include a heating or cooking step to kill pathogens; consequently, raw vegetables and salads are commonly associated with foodborne outbreaks caused by cross-contamination.”

Most tempeh is pasteurized, killing the bacteria, but the CDC warns there should be more awareness about handling unpasteurized tempeh. For vegetarians, treat unpasteurized tempeh as you would meat, washing knives, cutting boards and hands after handling the product.