Foodborne viruses can be tough to prevent and mitigate. Some can’t be cultured, so they are difficult to analyze. Others aren’t affected even by strong disinfectants, so intervention is ineffective. In the past decade, an additional virus, hepatitis E, joined norovirus and hepatitis A as a top three concern for human food safety.

To tackle these challenging foodborne viruses that can cause serious human illnesses, the Food and Agriculture Organization of the United Nations and the World Health Organization (FAO/WHO) are holding a series of meetings focused on microbial risk. The first Joint FAO/WHO Meeting on Microbiological Risk Assessment (JEMRA) convened in September 2023 in Rome and focused on foodborne viruses of top concern for public health, analytical methods, and contamination indicators. The second meeting, which took place in February 2024 in Geneva, discussed prevention and intervention measures for these viruses. A third meeting is planned for later in 2024 and will focus on evaluating risk.

The final reports for the first two meetings are still in progress, with only summaries released so far. Experts involved in the meetings said significant advances have been made in the study of foodborne viruses; these have helped researchers understand the science of viral mitigation since the inaugural JEMRA meeting 16 years ago, a milestone event that was the first time the issue of viruses in foods was brought to international attention.

“We have improved norovirus surrogates and ways to study human norovirus, and we have better detection methods, like digital PCR,” says Kalmia Kniel, PhD, associate chair of the department of animal and food sciences at the University of Delaware in Newark. She adds that thermal treatments are often relied on to inactivate viruses, but there are promising non-thermal technologies being studied, including cold plasma, chlorine dioxide, and some chemical disinfectant combinations.

The Biggest Threats

Dr. Kniel chaired the 2023 meeting and was a member of the expert committee that reviewed recent scientific developments, data, and evidence associated with foodborne viruses. JEMRA will update and provide scientific advice to the Codex Committee on Food Hygiene, which requested the series of meetings. The Codex committee will use the information for its international recommendations and standards. The expert committee also considered trade implications of possible standards to ensure that food safety does not become a trade barrier.

In reviewing viruses associated with human foodborne illness, the expert committee identified human norovirus as the leading cause of viral foodborne illnesses, followed by hepatitis A and hepatitis E. The ranking considered the frequency of illness, the clinical severity of the disease, and the food most often linked to the virus; however, while hepatitis A and hepatitis E were ranked equally behind norovirus in terms of frequency, they were higher than norovirus in terms of clinical severity. The committee lacked sufficient data to rank other viruses, including rotavirus and sapovirus.

In terms of the foods most associated with the viruses as a potential public health threat, prepared food, frozen berries, and shellfish—in that order—are associated with norovirus. For hepatitis A, linked foods are shellfish, frozen berries, and prepared foods. Those two viruses are transmitted via contamination by feces exposure. For hepatitis E, a zoonotic virus, pork and wild game are associated, and the virus is transmitted from animal to human.

The committee considered only water used in food production, in processing, in preparation, or as an ingredient, not water intended only for drinking, in its assessments.

Viral foodborne disease has a substantial impact on morbidity and mortality globally, but surveillance data is sparse, and there is the potential for asymptomatic shedding, so it is difficult to craft prevention and control strategies.

Norovirus causes about 125 million cases of foodborne illness and 35,000 deaths worldwide annually, according to the committee’s summary, including severe outcomes such as hospitalization and death, especially in children younger than five years old, the elderly, and immunosuppressed people, who may shed the virus for extended periods. Hepatitis A causes about 14 million cases of foodborne illness and 28,000 deaths each year globally, but there are significant regional differences attributable to endemic prevalence, vaccine use, and international food trade. There are no global estimates for hepatitis E, which can damage the liver, the meeting summary said.

“The JEMRA committees discuss foodborne viruses in a global context,” Dr. Kniel said. “We need to keep in mind that our food system is global in nature, which means we need better surveillance of viruses in all countries in order to help each other.”

Dr. Kniel said that since the 2008 JEMRA report, international and national standard methods have been developed and validated to detect and quantify human norovirus and hepatitis A virus in foods. Methods released since that report include the International Standards Organization’s ISO-15216-1:2017 and ISO-15216-2-2019. These are used widely to detect norovirus and hepatitis A in leafy greens, soft fruits, and shellfish, and as a benchmark to validate new methods, the committee’s summary said. There is no ISO method for prepared foods. Methods to detect hepatitis E in meats are under development.

The committee said infectivity assays are needed for wild-type viruses, as there still is no definitive way to tell infectious from noninfectious viruses using molecular amplification.

It recommended that countries consider building capacity to help with adopting and training in methods for detecting viruses in foods and the environment. “Appropriate global actions will help alleviate the anticipated increase in public health risk from viral foodborne illness arising from population growth, the climate crisis, and globalization of food supply chains,” the summary from the 2023 meeting said.

Prevention and Mitigation

Prevention is the preferred focus now, given the difficulty and expense of mitigating infected foods, says Lee-Ann Jaykus, PhD, rapporteur of the March 2024 meeting and a member of its expert committee. She says the viruses are not culturable organisms and cannot be grown in a lab like bacteria can, nor can they be culturally enriched. There is no host cell in a culture with which to propagate them. It’s necessary to concentrate and purify them from a sample and use reverse transcription polymerase chain reaction to detect the viruses. “We have standardized methods to detect these viruses in selected commodities, but they have some inherent disadvantages because of the limitations of not having a culture,” Dr. Jaykus says.

Limitations include the fact that even when a viral nucleic acid is detected, it doesn’t necessarily mean there is an infectious virus, she said. Real-time polymer chain reaction (RT-PCR) is a complicated method, and it is easy to lose viruses in the first steps, so it is not as sensitive as needed. “These are limitations not because the science is bad,” she says. “The science is the best it can be as it currently stands. There are limitations because we can’t grow these things.”

One focus of the second meeting was contamination routes for the virus to humans. Fecal matter and vomit from infected humans are the primary sources of contamination for norovirus and hepatitis A to get to humans through affected waters, food handlers carrying the viruses, and surfaces, because the viruses can live for weeks on surfaces, Dr. Jaykus says. The zoonotic hepatitis E virus is present in the meat, organs, tissues, and excretions of infected swine and game animals and gets transmitted through exposure.

Because the viruses persist in the environment for long periods and are resistant to many treatments, prevention is the key strategy to control foodborne viruses, Dr. Jaykus says. One example of prevention is reducing the viral load in shellfish by treating wastewater, but that requires infrastructure investment. Another is using production-related strategies to reduce contamination of fresh and frozen produce. Virus inactivation methods also are under investigation.

The committee recommended some directions for future research and development, including early identification of contamination hotspots using wastewater surveillance, for example, and technologies such as satellite imagery and hydrographic dye studies to predict virus dispersion. It also recommended using emerging scientific data to develop surface disinfectants and hand sanitizer formulations with greater efficacy against environmentally stable viruses. After all, hand sanitizers were effective in reducing transmission during the COVID-19 pandemic.

“Following up on the COVID-19 pandemic, it is critical that we launch surveillance studying the health of animals, humans, and the environment to identify important zoonotic viruses before the next pandemic,” says Dr. Kniel, who, like Dr. Jaykus, was surprised to see the hepatitis E virus added to the list of top foodborne virus concerns since the inaugural JEMRA meeting 16 years ago. “It is frustrating to continually talk about the need for better surveillance to better understand foodborne virus transmission and the attribution of disease to a specific virus.”

Table 1: Foodborne viruses and foods of highest public health concern

Source: FAO/WHO.

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FDA, along with Centers for Disease Control and Prevention and state and local partners are investigating a multistate outbreak of hepatitis A infections in the United States linked to fresh organic strawberries.

These potentially contaminated strawberries were imported from Baja California and branded as FreshKampo and HEB by a common supplier; they were purchased between March 5, 2022, and April 25, 2022. The Public Health Agency of Canada and the Canadian Food Inspection Agency are also investigating an outbreak of hepatitis A; imported fresh organic strawberries have been identified as the likely source of that outbreak.

Currently, the potentially contaminated FreshKampo and HEB products are past shelf life. Consumers who purchased these brands of fresh organic strawberries between March 5, 2022, and April 25, 2022, and then froze those strawberries for later consumption should not eat them.

These products may have been sold at the following retailers, including, but not limited to:

• HEB
• Kroger
• Safeway
• Sprouts Farmers Market
• Trader Joe’s
• Walmart
• Weis Markets
• WinCo Foods

Epidemiologic and traceback data show that fresh organic strawberries are a likely source of illness in this outbreak. Illness onset dates range from March 28 to April 30, 2022. Records from outbreak-associated cases in California and Minnesota show cases having purchased FreshKampo brand fresh organic strawberries prior to becoming ill.

This investigation is ongoing, and additional products may be included. FDA will provide more information as it becomes available.

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The FDA is collecting samples of frozen berries from processors, distribution centers, warehouses, and retail locations throughout the year to test for hepatitis A virus and norovirus.

The sampling assignment began in November and is estimated to last approximately 18 months. FDA is collecting domestic samples of frozen berries. It is also collecting import samples from ports of entry, importer warehouses, or other storage facilities where foreign goods are cleared for entry into the country. The agency plans to collect and test 2,000 samples in all.

Some consumers use frozen berries as ingredients in foods without first cooking them, increasing their risk of exposure to harmful viruses, says FDA. The agency reported three hepatitis A virus outbreaks and one norovirus outbreak linked to frozen berries in the U.S. from 1997 to 2016.

Strawberries, raspberries, and blackberries are delicate and may become contaminated with bacteria or viruses if handled by an infected worker who does not use appropriate hand hygiene, or if exposed to contaminated agricultural water or a contaminated surface, like a harvesting tote. Freezing preserves berries but generally does not kill viruses, which can survive at low temperatures.

If FDA detects hepatitis A virus or norovirus in a sample, the agency will notify the firm of the finding(s) and work with the firm to take appropriate action. Upon detecting a positive test result, FDA may also take actions such as placing a firm on an import alert, overseeing a recall, or issuing public warnings.

The FDA will post the sampling results on its FY 19-20 Frozen Berries Assignment page on a quarterly basis and will publish an analytical report once the assignment is complete.

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Image Credit: © whitestorm – Fotolia.com

The Hepatitis A virus (HAV) is a non-enveloped, single stranded RNA virus that is classified in the Picornaviridae family. HAV is a liver disease that results from exposure to virus particles. The virus is primarily spread via the fecal-oral route—when an uninfected person ingests water or food that is contaminated with the feces of an infected person. HAV can be spread through contaminated water, inadequate sanitation, or poor personal hygiene by food handlers.

Severity of illness from HAV can range from a mild illness lasting a few weeks to a severe illness lasting several months. Symptoms of Hepatitis A include: fever, fatigue, abdominal discomfort, nausea and vomiting, joint pain, loss of appetite, jaundice, clay-colored bowel, and dark urine.

According to the World Health Organization, HAV is one of the most frequent causes of foodborne infection, with a yearly estimate of 1.4 million cases worldwide. The largest foodborne outbreak of HAV occurred in Shanghai in 1998, affecting 300,000 people. The source of that outbreak was determined to be clams harvested from sewage-polluted waters.

The most common sources of foodborne HAV contamination are oysters, mussels, fruits, and vegetables. Fresh produce, such as salad, strawberries, raspberries, blueberries, and vegetables, have increasingly been implicated in foodborne outbreaks of Hepatitis A.

Risk

Individuals who have not been vaccinated or previously infected are at risk to contract HAV. In developed countries, such as the U.S., good sanitation and hygiene conditions keep HAV infection rates low. However, in developing countries, HAV is endemic and a majority of infections occur during childhood. Once infected with the virus, individuals develop antibodies to the virus, resulting in a lifelong immunity from contracting HAV again.

Hepatitis A in foods is a result of fecal contamination. Individuals infected with HAV excrete large numbers of virus particles in their feces, which may continue for several months even after symptoms have subsided. The long duration of virus particle shedding is the main source of spreading HAV via the fecal-oral route or through water contaminated with sewage.

Foodborne contamination with HAV typically occurs when the produce is grown in a region of the world where there is a high incidence of Hepatitis A. Any food that is handled using poor hygienic practices or harvested under poor sanitation conditions could potentially become contaminated.

Any food that is handled using poor hygienic ­practices or harvested under poor sanitation conditions could potentially become contaminated.

Fruits and vegetables are typically consumed raw and can become contaminated with fecal matter at any point during the growing, harvesting, packing, or serving of fresh produce. Therefore the regions of the world where produce is grown as well as potentially infected food handlers with poor hygiene practices can be potential sources of foodborne HAV contamination.

In the last decade, documented HAV outbreaks have been linked to lettuce, strawberries, blueberries, raspberries, and green onions. Since 2012, frozen berries have been linked to several outbreaks in Europe, totaling 601 cases with three deaths. It was also linked to frozen berries in the U.S. In 2013, pomegranate seeds from Turkey were linked to an outbreak that affected 159 people.

Image Credit: © Julián Rovagnati – Fotolia.com

As recently as February of this year, a HAV outbreak occurred in Australia affecting at least 14 people. Once again, frozen berries were identified as the most likely source of the contamination. The implicated product contained raspberries that were packed in China; however, the exact source of the contamination has not yet been identified.

Prevention

Strategies designed to reduce or prevent the risk of foodborne outbreaks of Hepatitis A should focus on preventing foods from becoming contaminated during growing, harvesting, and packaging. In developing countries, clean water should be used for the irrigation, washing, and processing of produce.

Food handlers should be trained on proper hygiene, such as washing hands frequently and wearing gloves when handling ready to eat foods. The application of good agricultural practices is needed to improve hygiene in primary production areas. Providing workers in the fields with basic employee hygienic needs, such as toilet paper and handwashing facilities, can contribute to reducing the risk of contamination.

Moreover, in developing countries, it is important to keep young children, who may be asymptomatic carriers of HAV, away from areas where fresh produce is being grown and harvested.

The spread of HAV can be reduced by irrigating, growing, and processing produce in safe water using proper sewage disposal and training workers on proper personal hygiene. Food companies should be aware of the risk of HAV and knowledgeable about how they source fresh produce. It is recommended that businesses confirm that suppliers have proper hygiene measures in place and monitor the supply chain of their fresh fruits and vegetables. Monitoring can be done by periodically testing their produce for HAV using the current rapid detection methods available to screen for HAV.

Cipriani is research project leader for Merieux NutriSciences. Reach her at andrea.cipriani@mxns.com.

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