Tainted Tempeh

Tempeh found to be Salmonella vehicle for first time in 2012 outbreak

/ Author:  / Reviewed by: Joseph V. Madia, MD Beth Bolt, RPh

(RxWiki News) Salmonella, the notorious foodborne bacteria, is often associated with animal products like chicken or eggs. But a recent study from the CDC explored a new vehicle for the bacteria — a vegetarian meat substitute called tempeh.

Researchers found that contaminated tempeh caused 89 Salmonella infections in a 2012 North Carolina outbreak. 

This study highlighted the need for careful handling of the product and warned against the dangers of cross-contamination, which can happen when Salmonella or another bacteria moves to surfaces or utensils and then on to other foods. 

"Clean kitchen work surfaces and utensils carefully."

This study, led by Stephanie E. Griese, MD, of the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia, closely examined the tempeh-spread outbreak of Salmonella enterica in 2012.

According to the study authors, tempeh is "a fermented bean product that is usually pasteurized and cooked before consumption."

A total of 89 infections were reported in the outbreak, which led to eight hospitalizations and luckily, no deaths. The patients all became ill between February 29 and May 8, 2012.

Five states reported Salmonella infections connected to the outbreaks, but the vast majority (81 patients) were residents of North Carolina. More specifically, 80 had traveled to or lived in Buncombe County (home to the city of Asheville) during the period they were likely exposed to the bacteria. 

Two of the patients were healthcare providers, 10 were food service workers and 39 were students of or visitors to a university in Buncombe County.

Symptom-related information was available for 86 of the patients. All 86 of these patients experienced diarrhea lasting from two to 24 days. Of the 82 patients who responded to a question about bloody diarrhea, 30 (37 percent) experienced this symptom. 

According to the study authors, the patients commonly reported eating vegetarian foods. Questions about meat substitutes like tempeh and tofu were not routine in Salmonella investigations, so an outbreak-specific questionnaire was created to help pin down the source of the infections. 

Of the 41 initial patients to answer the questionnaire, 18 (44 percent) noted that they had eaten tempeh. Twelve reported eating the product at a restaurant, four at the university and two noted they had sampled tempeh in a grocery store. Two of the patients who had consumed tempeh were food service workers who handled the product at their jobs. 

Investigators visited the three restaurants most identified by the patients and noted some issues in the handling of the product.

"Interviews with managerial staff and observation of food preparation identified multiple opportunities for cross-contamination, including preparation of uncooked, unpasteurized tempeh on the same surfaces used to prepare ready-to-eat foods; failure to perform handwashing after handling uncooked tempeh; and bare-hand contact with ready-to-eat foods," reported Dr. Griese and team.

As the investigation continued, it was then discovered that the North Carolina Department of Agriculture and Consumer Services had found evidence of Salmonella in a certain brand of tempeh ("Brand A") during routine food testing. The unpasteurized (meaning it did not undergo a heating treatment to block certain bacteria) tempeh was produced in Buncombe County and served at 34 restaurants across the state, plus several grocery stores in other states and the university cafeteria. 

According to the study authors, the process of creating Brand A tempeh involved beans, vinegar and a starter culture for fermentation called Rhizopus spp. The starter culture tested positive for Salmonella.

Dr. Griese and team reported that both the finished tempeh and the Rhizopus spp. starter culture were voluntarily recalled once they were identified as a Salmonella source. 

This study brings to light the possibility of unpasteurized tempeh to serve as a vehicle for Salmonella, and highlights the dangers of cross-contamination, during which bacteria transfers to surfaces and then to other uncooked (ready-to-eat) foods, like salad ingredients. 

The study authors noted that in this outbreak, less than half of the responding patients remembered eating or handling tempeh, but all of them had eaten at a venue which served the product. This points to cross-contamination as a likely method of transmission. 

"Control measures addressing bare-hand contact with ready-to-eat foods, sanitation of food contact surfaces, and separation of raw and ready-to-eat foods were provided to restaurants that received Brand A tempeh and to the local Independent Restaurant Association," Dr. Griese and team noted.

"Although tempeh can be part of a healthy diet, public health considerations should focus on safe handling of unpasteurized tempeh to prevent illness," they concluded.

This study was published August 14 in the CDC journal Emerging Infectious Diseases. No conflicts of interest were reported.

Review Date: 
August 12, 2013
Last Updated:
August 15, 2013