Produce Spotlight: Blueberries

Blueberries are a major crop in Michigan and are popular throughout the United States. They are consumed fresh, frozen, or in processed food products. Because they are usually eaten raw, any contamination that occurs before, during or after harvest can affect the product consumers purchase. Although blueberries have caused relatively few foodborne outbreaks compared with other produce commodities, several outbreaks in the recent past show that they are not immune to contamination. As with other produce, proper handling during growing, harvesting, and packing is essential.

Recalls and Outbreaks

While outbreaks and recalls related to blueberries are not typically in the headlines, there have been issues in the past. On July 1st of this year, the FDA issued a recall of 12,000 pounds of organic blueberries due to positive tests for Listeria in the packing facility. Listeria was also involved in a recall of frozen blueberries in Oregon from several co-ops and markets, following routine environmental testing.

In 2010, six Salmonella cases were linked to fresh blueberries in Minnesota, all traced back to one grower. In 2009, a multi-state outbreak of Salmonella in blueberries was linked to 14 illnesses. In 2006, an E. coli outbreak tied to fresh blueberries led to six illnesses.

Crop Characteristics

Several characteristics of blueberries are important when creating an Agriculture Water Assessment:

• High moisture and soft skin: Berries have thin skin and high moisture content. When contaminated, pathogens can easily attach to or penetrate the surface of the berries.

• Grown in clusters: Blueberries are grown in clusters. This helps them retain water and moisture.

• Grown off ground: Blueberries are grown off ground, especially in high bush varieties. Leaving them less susceptible to flooding and ground splash during irrigation.

• Waxy coating: Blueberries have a waxy coating that repels water.

Other considerations:

• Ready‑to‑eat consumption: Blueberries are usually eaten raw or frozen. Freezing preserves pathogens rather than eliminating them, so contamination during harvest can remain through the point of consumption.

• Environmental contamination: Irrigation water from surface sources can be contaminated with pathogens. Fields may be exposed to wildlife, livestock, or poultry feces, which can harbor Salmonella, E. coli, and Listeria. Manure-based fertilizers and runoff from animal operations can also introduce pathogens.

• Human factors: Workers who harvest berries can transfer pathogens if they lack adequate, readily accessible toilet and handwashing facilities or proper hygiene training.

Practical Steps for Farmers to Reduce Risk

1. Implement Good Agricultural Practices (GAPs)

   Develop a food safety plan to assess water quality, soil amendments, worker health and hygiene, equipment sanitation, and recordkeeping. Use proper application intervals for irrigation water that may contact the harvestable portion of the crop and manures and composts. Completing an Agricultural Water Assessment will help determine and mitigate risks related to agricultural water.

2. Manage soil amendments carefully

   If using compost, ensure it has undergone a scientifically validated treatment process (e.g., ensuring compost has reached 131F for at least three days when static composting, or at least 15 days when turning, both followed by curing with proper management). If you choose to use raw (untreated) manure you must apply it in a manner that does not contact covered produce during or after application. Avoiding raw (untreated) manure applications during the growing season can help to minimize risks associated with human pathogens.

3. Control animal intrusion

   Install fencing to limit access by livestock and monitor for wildlife intrusion, mow the middle of the rows to reduce habitat for rodents, and remove cull piles promptly. Using bird and other animal deterrents where practical.

4. Provide and enforce worker sanitation

   Focusing on worker health and hygiene helps prevent contamination from employees. All farms should provide adequate, readily accessible handwashing facilities (112.130(a)) and ensure that employees use them before handling berries and throughout their work as required. Train all workers in proper handwashing techniques and ensure sick workers do not come to work. Regularly clean and sanitize harvest containers, especially if they have been contaminated.

Conclusion

While outbreaks linked directly to blueberries are rare, historical events show that contamination can occur. Developing a Food Safety Plan focused on training workers, monitoring environmental risks, cleaning and sanitizing of equipment and tools will help ensure that blueberries remain a safe and desirable crop.

Sources

Centers for Disease Control and Prevention. (2010). Multistate outbreak of Salmonella Newport infections linked to blueberries—Minnesota, 2010. https://pubmed.ncbi.nlm.nih.gov/23643117/

Food Poison Journal. (2020). A history of berry—especially strawberry—foodborne outbreaks. https://www.foodpoisonjournal.com/foodborne-illness-outbreaks/a-history-of-berry-especially-strawberry-foodborne-outbreaks-especially-hepatitis-a/

Food Safety News. (2023, July 18). Blueberries recalled over Listeria risk. https://www.foodpoisonjournal.com/food-recall/blueberries-recalled-over-listeria-risk/

Mody, R. K., Meyer, S., Trees, E., White, P. L., Nguyen, T., Sowadsky, R., ... & Griffin, P. M. (2011). Outbreak of Salmonella enterica serotype Newport infections associated with consumption of imported frozen raw ground tuna. Clinical Infectious Diseases, 54(5), 503–509.

University of California Agriculture and Natural Resources. (n.d.). Strategies for microbial decontamination of fresh blueberries and derived products. https://ucfoodsafety.ucdavis.edu

University of Maine Extension. (2020). Guidance on food safety for wild blueberry growers. https://extension.umaine.edu/blueberries/factsheets/food-safety/

U.S. Food and Drug Administration. (n.d.). Recalls [Data dashboard]. FDA Data Dashboard. https://datadashboard.fda.gov/oii/cd/recalls.htm