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Frozen berries are commonly used as ingredients in various foods. While they are often baked into pies and other goods, they are also used raw in fruit salads and smoothies, which have been linked to foodborne illness outbreaks. Between 1997 and 2016, the FDA reported three hepatitis A virus outbreaks and one norovirus outbreak linked to frozen berries. "While no enteric virus outbreaks associated with domestic berries have been reported in 35 years, there have been outbreaks linked to imported fresh and frozen berries," the FDA said in a statement. The most recent HAV outbreaks in the United States occurred in 2022 and 2023, with imported berries from the same grower identified as the source. "Outbreaks reported since 1997 have been linked to imported fresh and frozen berries. However, hygienic practices and challenges in controlling enteric viruses in berries and other hand-harvested produce apply globally." Enteric viruses, such as hepatitis A and norovirus, are primarily spread through the fecal-oral route, which occurs when food, water, or surfaces contaminated with fecal (or vomit) matter is consumed. For example, strawberries, raspberries, and blackberries can become contaminated with bacteria or viruses if handled by an infected worker who does not follow proper hygiene after using the toilet. Because berries are often eaten raw and are hand-harvested, they can be particularly vulnerable to contamination if strict hygiene practices are not followed. Contamination can also occur via water or surfaces during harvesting and packaging. Contrary to popular belief, freezing preserves berries but does not kill viruses, which can survive at low temperatures. Noroviruses, for example, can withstand temperatures as high as 145°F. According to the Centers for Disease Control and Prevention (CDC), norovirus outbreaks most commonly occur in healthcare facilities, restaurants, catered events, schools, childcare centers, and cruise ships, where food handling procedures maybe suboptimal due lack of training or compliance by workers.
What are Enteric Viruses?
Enteric viruses infect the digestive tract and cause symptoms such as nausea, diarrhea, vomiting, and stomach pain. Typically, a norovirus bout lasts 12 to 60 hours. These viruses are primarily spread through contact with feces or infected animals. People with weakened immune systems or underlying health conditions are at higher risk of severe illness. HAV symptoms can include fatigue, nausea, vomiting, abdominal pain, jaundice, dark urine, and pale stool.
The FDA attributed the contamination of imported berries to lapses in food safety systems and prevention measures by overseas suppliers. "Key factors to consider in preventing outbreaks include proper hygienic practices by field workers, management of sanitary facilities, prevention of cross-contamination during field and processing operations, and monitoring viral carriage among farm and facility workers," the agency stated.
HAV is a vaccine-preventable, short-term infection that does not become chronic. Most infected individuals recover completely within weeks. However, untreated infections can lead to severe complications in older adults, immunocompromised individuals, or those with underlying health issues.
FDA focuses on prevention and spread
To prevent future outbreaks, the FDA announced a strategy to minimize infection risks for the public. The plan includes:
- Promoting high compliance rates with FDA food safety requirements.
- Encouraging the berry industry to implement consistent pre- and post-harvest sanitary practices globally and to use root cause analysis when food safety failures occur.
- Expanding scientific knowledge about detecting and mitigating viruses in fresh and frozen berries, agricultural water, and production environments.
- Incentivizing public health measures, such as immunization programs, to promote worker health.
