In the U.S. between 2011 and 2023, non-dairy fermented foods (NDFFs) caused 39 foodborne illness outbreaks, resulting in 509 illnesses, 132 hospitalizations, and four deaths, according to a new analysis.

The analysis was authored by researchers with the U.S. Food and Drug Administration’s Human Foods Program (FDA’s HFP) and the U.S. Centers for Disease Control and Prevention’s National Center for Emerging and Zoonotic Infectious Disease (CDC’s NCEZID) and was published in the Journal of Food Protection. It provides novel information on NDFF outbreaks that can be used to better understand the safety of this food type and inform microbiological contamination control efforts.

Fermented and Cultured Food Illness Knowledge Gap

Fermented and cultured foods represent approximately one-third of the human diet, yet foodborne illnesses attributable to fermented foods may be underrepresented in the literature, according to the study.

Because food vehicles of illness are typically categorized by food type rather than how they were processed, cultured and fermented foods may not be distinguished from their raw ingredient source in outbreak reporting. The study sought to close this knowledge gap by determining the burden of illness attributable to NDFFs.

Clostridium, Salmonella—Most Prominent Pathogens

The researchers analyzed outbreaks reported to the Foodborne Disease Outbreak Surveillance System (FDOSS) from 2011 to 2023 for association with a nondairy fermented or cultured food vehicle. NDFF-associated outbreaks were further categorized by food vehicle type using the Interagency Food Safety Analytics Collaboration (IFSAC) Food Categorization Scheme. Outbreaks with unknown food vehicle sources or mixed sources were excluded from the analysis.

The 39 total outbreaks included in the analysis included 509 illnesses, 132 hospitalizations, and four deaths.

Clostridium botulinum caused the greatest number of outbreaks at 16 (or 47 percent of single-etiology outbreaks). Salmonella enterica caused the most illnesses at 307 (making up 64 percent of illnesses in single-etiology outbreaks).

Pathogen–Food Pairs Emerge 

Among the 28 confirmed, single-etiology outbreaks associated with an NDFF, the most frequently occurring pathogen–food category pair was C. botulinum linked to the “Other Aquatic Animals” category in six outbreaks involving goods like seal oil and whale. At the same time, S. enterica and cured pork products emerged as the pathogen–food pair responsible for the highest number of outbreak-associated illnesses (134) and hospitalizations (34), across two outbreaks.

Of the four deaths reported, two were attributed to C. botulinum; one linked to “Other Aquatic Animals” (i.e., whale) and one linked to “Fish” (i.e., fermented fish heads). The remaining two deaths were linked to L. monocytogenes-contaminated country-style deli ham and the other was linked to L. monocytogenes and Italian-style deli meats.

Also of note, four outbreaks linked to NDFFs were caused by meat and dairy alternatives, including cashew cheese in two outbreaks, and tempeh and fermented tofu in one outbreak each.

Outbreak Trend: Traditional Alaskan Fermented Products

Interestingly, Alaska reported NDFF outbreaks more frequently than any state, with 38 percent of all outbreaks (15) being in Alaska. Identified food vehicles included traditional Alaskan foods, including fermented black bear meat, fermented fish, fermented seal, and fermented whale.

The researchers explained in the study that C. botulinum has been cultured from coastal Arctic soils and fish, and that some preparation practices (e.g., seawater rinsing, holding meat on coastal rocks before fermentation) may provide additional opportunities for contamination. It has also been speculated that the transition from traditional woven baskets to plastic containers for food fermentation may support an anaerobic environment where spores may germinate more effectively.

Drivers of Fermented, Cultured Food Outbreaks 

With fermented foods of any kind, microbial contamination can occur before or during fermentation, including contaminated starting product or inadequate processing; after fermentation (postprocess cross-contamination); or when consumers handle the product. Because NDFFs are intended to be consumed without further cooking, the researchers stressed that proper fermentation practices and the use of preventive controls are essential for food safety.