Update (May 10, 2:00 p.m. Eastern): North Carolina’s Department of Public Health laboratory confirmed on Thursday that the ongoing Salmonella Paratyphi B outbreak linked to Smiling Hara unpasteurized tempeh was caused by contaminated packages of spore culture used in the product’s fermentation process.

At least 63 people in four states have been sickened in this outbreak.

According to the Buncombe County Department of Health, the U.S. Food and Drug Administration is now tracing the origin of the culture to identify the source of the contamination. The FDA is also investigating the potential for other outbreaks linked to the culture.

Update (May 4, 5:00 p.m. Eastern): The Buncombe County Health Department has declared Smiling Hara tempeh the source of the Salmonella Paratyphi B outbreak originating in Asheville, NC.

The number ill has risen to 46, with seven being hospitalized.

In a joint press conference with Smiling Hara, the county health department announced that the Salmonella strain found in a sample of Smiling Hara unpastuerized tempeh matches the outbreak strain.

Smiling Hara said they are waiting for test results on ingredients to determine the exact source of the Salmonella. According to the company’s website, their product is made with three ingredients: beans, vinegar and culture.

The company will continue to work with public health officials as the investigation continues.

The following article was published on the morning of May 4 before public health officials had determined the source of the outbreak. It explores how the tempeh — then a suspected source — may have been contaminated:

The outbreak of a rare, typhoidal Salmonella strain that originated in North Carolina’s Buncombe County grew to 40 confirmed illnesses on Thursday as the state and county health departments continue their investigation and anticipate additional infections will surface by the day. 

The strain, Salmonella Paratyphi B, is a less severe but especially contagious form of Salmonella that can lead to Typhoid fever in some of those it infects. According to Buncombe County Department of Health spokeswoman Gibbie Harris, many of those sickened contracted their infections through person-to-person contact.

On Monday, North Carolina-based company Smiling Hara recalled 12-ounce packages of unpasteurized tempeh as a cautionary measure after a sample of the company’s soybean tempeh tested positive for Salmonella. The tempeh remains a potential outbreak source until the state health laboratory can determine whether or not the strain of Salmonella in the tempeh is Paratyphi B.

State and county health officials have said tests might identify the strain sometime Friday, though they may take until Monday.

Either way, more than half of the cases involve individuals who say they did not consume tempeh during the outbreak window, Harris told Food Safety News. She said the health departments continue to investigate other potential sources, though it is clear that infections have come from “several different routes of transmission.”

Because public health officials are still interviewing victims, the health departments cannot confirm the exact number of individuals connected to the tempeh. Buncombe Country Public Information Officer Gaylen Ehrlichman said officials expected the majority of the new cases to result from person-to-person transmission.

Illnesses have been reported in North Carolina, South Carolina, Tennessee and New York. The first case was reported on February 28.

Smiling Hara has temporarily halted production of its tempeh and has been working with public health officials throughout the investigation. They have recalled all tempeh made between January 11 and April 11 with best-by dates of July 11 through October 25.

A raw food intended to be cooked

Smiling Hara’s tempeh was first fingered as a suspect in the outbreak after routine tests conducted by the state agriculture department came back positive for Salmonella.

When the initial test results came in, the company immediately warned customers and restaurants not to eat the soybean product until the Salmonella test could be confirmed. When they learned on Monday that the sample was indeed contaminated, they issued a complete recall.

“Smiling Hara has been absolutely cooperative. They’re incredibly socially conscious,” Harris said.

Sarah Yarney, marketing director for Smiling Hara, told Food Safety News that lab tests show the Salmonella could be coming from one of their ingredients and they should have more detailed information soon. The company’s website states that they only use three ingredients: beans, vinegar and culture.

Just weeks before their routine inspection, Smiling Hara revised its labels to include a notice to customers that read, “THIS IS A RAW FOOD AND IS INTENDED TO BE COOKED,” along with cooking instructions on the back, Yancey said. The decision to include that information was not related to any illnesses.

Tempeh is a firm, caked bean product often made from soybean that sometimes functions as a meat substitute in meals. Its production involves natural culturing and fermentation to bind the beans together and theoretically help eliminate bacteria.

While many brands of tempeh are pasteurized to kill potential pathogens before sale, Smiling Hara’s is sold unpasteurized in an effort to retain digestive enzymes and probiotics, the company’s website states. The website also informs customers that they need to cook the food before eating.

Assuming the tempeh may be linked to the outbreak, Harris fears many customers might have made simple mistakes in handling the tempeh, even if they cooked it.

“Many people think of tempeh as a vegetable, so they don’t feel the need to clean a cutting board or other surface before cutting vegetables there and that’s an opportunity for cross contamination,” Harris said. “With this outbreak, people are being educated that tempeh is a protein source and should be treated like meat.”

Contamination remains a mystery

Until the public health investigation unearths more details, even experts can only hypothesize over how the tempeh could have become contaminated with Salmonella, whether it’s related to the Paratyphi B outbreak or not.

North Carolina State University food science professor Fletcher Arritt told Food Safety News that tempeh production can vary significantly from one manufacturer to another. The number of variables involved makes it essentially impossible to predict how contamination might occur.

As Arritt explained: Unlike fermentation processes that acidify products, tempeh’s  process instead eliminates the acidity provided by the vinegar, elevating the product’s pH back to one that supports microbial reproduction. Combine that with an incubation of 12 to 36 hours at 80 or 90 degrees, and you have a potential breeding ground for bacteria.

“At what point in time does the pH get high enough? When’s the crossover point and how many hours of incubation does that leave? It varies from producer to producer,” Arritt said. “In the event that you have contamination at the point of incubation, there’s the possibility for [pathogen] growth.”

Arritt pointed out that some scientific literature points to the antimicrobial qualities of Rhizopus, the fungus inoculated in tempeh fermentation, as a deterrent to gram-positive bacteria growth including Staphylococcus aureus (staph infection) and Bacillus subtilis.

That literature, however, appears to be incomplete. Rhizopus may eliminate Staphyloc
occus, but is it as effective against Salmonella?

“In my reviewing of the literature, there are certainly circumstances where [Rhizopus] may be effective, but I don’t know if there’s enough antimicrobial ability to overcome any contamination,” Arritt said. “There’s also always a potential for post-process contamination.”

As the investigation into Smiling Hara’s tempeh continues, the details may help answer some of these questions about Rhizopus, he added.

Big questions await answers

Arritt has worked with food producers at the commercial kitchen facility, owned by Blue Ridge Food Ventures, where Smiling Hara produces its tempeh. Blue Ridge halted all production at the facility upon learning of the Salmonella investigation in order to conduct “extensive” environmental testing.

“Blue Ridge has been very proactive. They’ve done swab tests and they’ve got safety policies and procedures in place,” said Daniel Ragan, director of the North Carolina Department of Agriculture’s Food & Drug Protection Division.

The results of those swab tests should be available soon, the company has said. Approximately 20 local food companies rent kitchen space to make products at Blue Ridge’s facility.

The department of agriculture inspects all food producing facilities once a year. Their annual inspection prompted the testing of Smiling Hara’s tempeh sample in the first place.

“Smiling Hara has been very cooperative, too,” Ragan added. “Until we make a connection to the outbreak, all we have is a product that tested positive for Salmonella.”

Arritt agreed that the questions will remain until test results provide more answers in the coming days.

“This is an unfortunate thing for the company. They’re trying to do the right thing,” he said. “There seems to be a possible connection [to the outbreak], but we’re going to have to wait for all the facts to get out on the table.”