Shellfish, fresh produce, and frozen berries are the foods most consistently linked to hepatitis A outbreaks worldwide. The virus spreads through fecal contamination of food or water, and it thrives in items that are eaten raw or only lightly processed. What makes certain foods riskier than others comes down to how they are grown, harvested, and handled, and to an unusual trait of the virus itself: it is remarkably hard to kill.
Shellfish and the Filter-Feeding Problem
Oysters, clams, mussels, and cockles top the list of hepatitis A-associated foods, and they have for decades. These animals are filter feeders, meaning they pull large volumes of water through their bodies to extract nutrients. If that water contains even trace amounts of sewage, the shellfish concentrate the virus in their tissues at levels far higher than what exists in the surrounding water. One study examining experimentally contaminated oysters found that even after seven days of depuration (the industry-standard cleansing process, where shellfish are held in clean water to purge contaminants), the virus was still detectable in over 90% of the digestive glands and gills.1International Journal of Food Microbiology. Localization and persistence of hepatitis A virus in artificially contaminated oysters
The reason depuration falls short is that the virus lodges deep inside shellfish tissue, not just on surfaces. Researchers found hepatitis A virus in the digestive diverticula, connective tissues, stomach, intestine, and gills of oysters.1International Journal of Food Microbiology. Localization and persistence of hepatitis A virus in artificially contaminated oysters Work on mussels showed similar results: depuration reduced viral levels by roughly 90%, but the remaining contamination was still high enough to cause infection.2PubMed. Effectiveness of depuration for hepatitis A virus removal from mussels (Mytilus galloprovincialis) A separate study comparing how quickly different microorganisms are purged from oysters and clams found that common bacterial indicators like E. coli left shellfish tissue much faster than hepatitis A virus did.3PubMed. Removal of Escherichia coli, Enterococcus fecalis, coliphage MS2, poliovirus, and hepatitis A virus from oysters (Crassostrea virginica) and hard shell clams (Mercinaria mercinaria) by depuration This matters because regulatory testing often checks for bacteria as a stand-in for viral safety. Shellfish that pass bacterial tests can still carry infectious hepatitis A.
Green Onions and Fresh Produce
The largest documented foodborne hepatitis A outbreak in United States history was traced to green onions served at a Pennsylvania restaurant in November 2003. The contaminated onions had been imported from a farm in Mexico, and by the time the outbreak was contained, hundreds of people were sick.4PubMed. An outbreak of hepatitis A associated with green onions What made that outbreak so revealing, beyond its sheer size, was follow-up research showing how the contamination likely happened. Investigators demonstrated that the virus can be taken up through the roots of growing onions and incorporated into the plant’s internal tissues, not just deposited on the surface.5PubMed. Green onions: potential mechanism for hepatitis A contamination Once inside, washing has no effect. You could scrub those onions thoroughly and the virus would still be there.
Fresh vegetables more broadly become contaminated when grown in or irrigated with water containing sewage. A study in Egypt detected hepatitis A virus in both fresh vegetables and the irrigation water used to grow them, underscoring that this is a live concern wherever water sanitation is unreliable.6Biomedical Journal of Scientific & Technical Research. Detection of Hepatitis A Virus in Fresh Vegetables and Irrigation Water: An Unseen Health Risk in Damanhur, Egypt Lettuce, herbs, and salad greens are often mentioned in outbreak reports because they are eaten raw, giving the virus a direct route into your body without any cooking step to reduce it.
Frozen Berries and Imported Fruit
Frozen berries, especially strawberries, have caused repeated multinational outbreaks and deserve their own category on the risk list. Freezing does not destroy hepatitis A; the virus survives cold storage easily, so contaminated berries remain infectious indefinitely in your freezer. Two outbreaks in the United States in 2022 and 2023 were both traced to fresh and frozen organic strawberries from a single grower in Baja California, Mexico.7PubMed. Investigation of Two Outbreaks of Hepatitis A Virus Infections Linked to Fresh and Frozen Strawberries Imported from Mexico – 2022-2023
Europe has dealt with the same pattern. In 2018, twenty hepatitis A cases appeared across six counties in Sweden over three months. Investigators identified imported frozen strawberries produced in Poland as the source, and genetic sequencing confirmed that the virus strain in the patients matched the strain found in the berries. Sharing that genetic data internationally turned up fourteen additional cases in Austria linked to the same producer.8PubMed Central. Hepatitis A outbreak linked to imported frozen strawberries by sequencing, Sweden and Austria, June to September 2018 A 2013 outbreak in Ireland was linked to frozen berries consumed in multiple forms: berry cheesecake, whole frozen berries, and yogurt containing frozen berries. Over 90% of the people who got sick had consumed at least one product containing frozen berries.9PubMed. Outbreak of hepatitis A infection associated with the consumption of frozen berries, Ireland, 2013–linked to an international outbreak
The recurring theme with frozen berries is that the contamination typically happens at the point of harvest or packing in a country where hepatitis A is common and sanitation practices may be inadequate. Because the berries are frozen soon after and exported internationally, a single contaminated batch can end up in kitchens across multiple countries. And because people often eat frozen berries without cooking them, in smoothies, on cereal, or in desserts, the virus reaches the consumer intact.
Semi-Dried Tomatoes and Unexpected Culprits
Not all hepatitis A-associated foods are obvious. Semi-dried tomatoes, a product most people would not immediately associate with foodborne virus risk, caused outbreaks in France, Australia, and the Netherlands between 2009 and 2010.10PubMed Central. Hepatitis A Associated with Semidried Tomatoes, France, 2010 The virus survives the partial dehydration process used to make these tomatoes, and the product is typically eaten without further cooking.11PubMed. Comparison of two extraction methods for the detection of hepatitis A virus in semi-dried tomatoes and murine norovirus as a process control by duplex RT-qPCR
In principle, any ready-to-eat food handled by someone who is infected can become a vehicle. An early and well-documented case involved a picnic where tuna salad sandwiches prepared by an infected person made seven of eleven attendees sick. The number of sandwiches each person ate was inversely related to how long it took them to develop symptoms, meaning those who ate more got sick faster.12American Journal of Public Health. An outbreak of foodborne hepatitis A showing a relationship between dose and incubation period That finding underscores something worth remembering: hepatitis A from food is dose-dependent. The more virus you consume, the shorter the time before you feel it.
Why Hepatitis A Is So Hard to Remove From Food
The reason so many different foods appear on this list is that hepatitis A virus is unusually tough. Most foodborne pathogens can be managed by refrigeration, mild acidity, or standard kitchen hygiene. Hepatitis A shrugs off all three. It survives on fruits and vegetables for days, and research on hand-to-food transfer shows that brief casual contact between contaminated hands and clean food can move roughly 10% of the virus present on the skin to the food’s surface.13PubMed Central. Foodborne spread of hepatitis A: Recent studies on virus survival, transfer and inactivation
The virus is also resistant to heat, radiation, and chemical disinfectants compared to many other foodborne pathogens.13PubMed Central. Foodborne spread of hepatitis A: Recent studies on virus survival, transfer and inactivation Its acid stability is striking: highly purified hepatitis A virus remained infectious after eight hours of exposure to pH 1 at room temperature.14PubMed. Acid stability of hepatitis A virus For context, your stomach acid sits at roughly pH 1.5 to 3.5. This means the virus can survive the trip through your digestive system with relative ease, which is exactly why it spreads through the fecal-oral route so effectively.
Thorough cooking does reduce the risk. Heating food to an internal temperature above about 85°C (185°F) for at least one minute is generally considered sufficient. But the foods most commonly linked to outbreaks, raw shellfish, salads, fresh berries, green onions used as garnish, are precisely the ones people tend to eat without cooking or with minimal heat treatment. That is the crux of the problem: the virus is resilient, and the foods it contaminates are often the ones you eat raw.
How Contamination Happens Before Food Reaches You
There are two broad routes by which hepatitis A gets into food. The first is environmental contamination during growing or harvesting. Crops irrigated with sewage-tainted water, shellfish harvested from waters near sewage outfalls, and berries picked by workers without access to adequate sanitation facilities all fall into this category. The outbreaks tied to imported produce tend to follow this pattern: the contamination occurs at the source, often in a country where hepatitis A circulates at higher rates and where food safety infrastructure is limited.7PubMed. Investigation of Two Outbreaks of Hepatitis A Virus Infections Linked to Fresh and Frozen Strawberries Imported from Mexico – 2022-2023
The second route is direct contamination by an infected food handler. A person shedding hepatitis A virus can contaminate any food they touch, and since the virus is shed for about two weeks before symptoms appear, the person typically has no idea they are infectious. This is how restaurants and catering events become outbreak settings. It is also how foods that would otherwise have no connection to hepatitis A, sandwiches, salads, pastries, any dish assembled by hand, can become vehicles. The 10% hand-to-food transfer rate noted in research means even brief handling is enough.13PubMed Central. Foodborne spread of hepatitis A: Recent studies on virus survival, transfer and inactivation
Tracing Outbreaks Back to Specific Foods
One reason hepatitis A outbreaks are difficult to link to specific foods is the long incubation period. Symptoms typically appear two to six weeks after exposure. By then, the implicated food is gone, the leftovers have been thrown away, and the affected person may not even remember what they ate. Investigators rely on detailed questionnaires, statistical comparison of what sick people ate versus what matched healthy people ate, and increasingly on genetic sequencing of the virus itself.
Advances in whole genome sequencing have made source identification considerably more precise. A recent study developed methods to extract and sequence complete hepatitis A genomes from contaminated clam samples, even when viral levels were low.15PubMed Central. Whole genome sequencing of hepatitis A virus: adapting Illumina protocols for foodborne investigation Earlier work established methods for detecting the virus in shellfish at extremely low concentrations using nested reverse transcription PCR.16PubMed. Detection of hepatitis A virus in shellfish by nested reverse transcription-PCR Newer rapid-detection tools have been validated across multiple food types, including green onion, strawberry, mussel, and milk, with the ability to pick up very small amounts of virus.17PubMed Central. Rapid Detection of Hepatitis A Virus in Foods Using a Bioluminescent Assay in Real-Time (BART) and Reverse Transcription Loop-Mediated Isothermal Amplification (RT-LAMP) Technology
The practical value of these technologies was demonstrated clearly in the 2018 Swedish-Austrian strawberry outbreak. When investigators sequenced the virus from patient samples and found a 100% genetic match to virus recovered from a specific batch of frozen strawberries, there was no ambiguity about the source. That batch was withdrawn and the producer identified.8PubMed Central. Hepatitis A outbreak linked to imported frozen strawberries by sequencing, Sweden and Austria, June to September 2018 Without sequencing, linking cases spread across two countries to a single Polish strawberry producer would have been far harder.
Practical Steps That Actually Reduce Your Risk
If you eat raw shellfish regularly, your risk profile for hepatitis A is genuinely higher than average. Cooking shellfish thoroughly, steaming until shells open and then continuing for several more minutes, brings the internal temperature high enough to inactivate the virus. Eating oysters raw on the half shell is the highest-risk way to consume them.
For produce, thorough washing helps remove surface contamination but cannot reach virus that has been internalized during growth, as the green onion research showed. When you are traveling in regions where hepatitis A is common, sticking to cooked foods and peeled fruits is a well-established precaution. At home, the biggest controllable risk factor is hand hygiene during food preparation. The research on hand-to-food virus transfer suggests that careful handwashing, particularly after using the bathroom and before handling food, is one of the most effective preventive measures available.
Vaccination remains the most reliable form of protection. A single dose provides strong immunity within two to four weeks, and completion of the two-dose series provides long-lasting protection. For people who travel to high-risk areas, work in food service, or simply eat a lot of raw shellfish or imported produce, vaccination eliminates most of the worry about which specific food might carry the virus on any given day.
High-Pressure Processing and the Shellfish Industry
Because standard depuration fails to fully clear hepatitis A from shellfish, the food industry has explored alternative approaches. High-pressure processing, which subjects food to extremely high pressures without heat, has shown promise. Laboratory work demonstrated that hepatitis A virus could be reduced to undetectable levels in tissue culture medium after exposure to pressures above 450 megapascals for five minutes, and meaningful reductions occurred at pressures between 300 and 450 megapascals.18PubMed. Inactivation of hepatitis A virus and a calicivirus by high hydrostatic pressure This technology is already used commercially for some oyster products, where it has the added benefit of making the shells easier to open. Whether it can be scaled economically across the global shellfish supply is another question, but for consumers, seeing “HPP” or “high-pressure processed” on a shellfish product label means an additional layer of viral safety beyond what depuration alone provides.
The gap between what current industry-standard cleaning achieves and what would be needed to reliably eliminate hepatitis A from shellfish is real. Depuration works well for bacteria, which is what regulators traditionally test for, but the virus lingers in tissue compartments that clean water cannot reach efficiently. Until regulatory testing catches up with this mismatch, the safest approach for raw shellfish remains either thorough cooking, high-pressure processing, or sourcing from waters with robust sewage management, none of which fully eliminates the possibility but all of which substantially lower it.