Introduction
Fresh and frozen common berries (i.e., blackberries, blueberries, raspberries, and strawberries) are popular and healthy foods. When berries are picked for fresh consumption, they are either placed directly in retail containers in the field or packed in a packinghouse without washing because they are highly perishable. Berries may be washed before freezing, but they are not usually blanched or heat-treated unless they are used in preserves or other processed products. Thus, there is typically no "kill step" that would eliminate pathogens in fresh or frozen berries.
Berries may be served mixed with other foods, such as in salads or desserts, and these foods may contain more than one kind of berry or other fruit. Epidemiologists have more difficulty accurately determining the food vehicle during a foodborne illness outbreak when the outbreak is associated with mixed foods, such as mixed berries. The viral and parasitic pathogens that have caused outbreaks associated with consumption of berries are difficult to detect in foods. The laboratory methods used to detect these pathogens have only recently been developed or are still under development. In November 2018, FDA began a 2-year survey of frozen berries (strawberries, raspberries, and blackberries) for the presence of norovirus and hepatitis A. As of September 30, 2019, 812 samples (339 domestic and 473 imported) had been screened. Of the frozen berries sampled, genetic material from hepatitis A virus was found in five samples (three domestic: one strawberry, one raspberry, and one blackberry; two imported: two raspberry) and genetic material from norovirus in eight samples (three domestic: one strawberry, two raspberry; five imported: two strawberry, one raspberry, two blackberry). At the time of publication, testing is ongoing; the FDA's plan is to test 2,000 samples (1,000 domestic and imported each) over 2 years.
This publication serves as a reference for anyone concerned about the safety of fresh and frozen berry products. Providing information for those who grow, harvest, process, transport, and serve berries to consumers is important for improving science-based food safety programs for the entire supply chain. Table 1 lists the reported outbreaks of foodborne illness from 1983 through 2019 in which specific berries or mixed berries have been identified as the food vehicle. Table 2 lists the reported outbreaks in which berries were likely the food vehicle.
Credit: © Peter Close (iStock)
References
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Falkenhorst, G., L. Krusell, M. Lisby, S. B. Madsen, B. Bottiger, and K. Molbak. 2005. "Imported Frozen Raspberries Cause a Series of Norovirus Outbreaks in Denmark, 2005." Euro Surveill. 10 (9): E050922.2.
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Maunula, L., M. Roivainen, M. Keranen, S. Makela, K. Soderberg, M. Summa, C. H. von Bonsdorff, M. Lappalainen, T. Korhonen, M. Kuusi, and T. Niskanen. 2009. "Detection of Human Norovirus from Frozen Raspberries in a Cluster of Gastroenteritis Outbreaks." Euro Surveill. 14 (49): pii:19435.
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Murrow, L. B., P. Blake, and L. Kreckman. 2002. "Outbreak of Cyclosporiasis in Fulton County, Georgia." Georgia Epidemiol. Rep. 18 (1): 1–2.
Niu, M. T., L. B. Polish, B. H. Robertson, B. K. Kanna, B. A. Woodruff, C. N. Shapiro, M. A. Miller, J. D. Smith, J. K. Gedrose, M. J. Alter, and H. S. Margolis. 1992. "Multistate Outbreak of Hepatitis A Associated with Frozen Strawberries." J. Infect. Dis. 166 (3): 518–524.
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Oregon Public Health. 2011. "Fresh Strawberries from Washington County Farm Implicated in E. coli O157 outbreak in NW Oregon." Accessed September 2013. https://web.archive.org/web/20121012143345/http://www.oregon.gov/OHA/news/2011/2011-0808.pdf.
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Rothschild, M. 2012. "BC Issues Warning about Pomeberry Frozen Berries." Food Safety News. Accessed April 2013. https://www.foodsafetynews.com/2012/04/bc-issues-warning-about-pomeberry-frozen-berries/.
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Terry, L. 2011. "Oregon Confirms Deer Droppings Caused E. coli Outbreak Tied to Strawberries." The Oregonian. Accessed September 2013. http://www.oregonlive.com/washingtoncounty/index.ssf/2011/08/oregon_confirms_deer_droppings.html.
Tables
Foodborne illness outbreaks associated with common berries as the food vehicle, 1983 through 2019.