Hepatitis A is one of the oldest and most important foodborne and waterborne viral diseases known to public health. Unlike many food poisoning pathogens, Hepatitis A is not a bacterium that multiplies in food, produces toxins, or causes illness within hours. It is a human virus that uses food, water, hands, surfaces, and close contact as vehicles to move from one infected person to another. Its target is the liver, but its route of travel is usually the mouth. That combination makes Hepatitis A both biologically distinctive and epidemiologically difficult to control. A microscopic amount of fecal contamination can be enough to spread the virus, and because infected people can shed virus before they know they are sick, outbreaks often begin silently.
Hepatitis A virus, commonly called HAV, causes an acute infection of the liver. The word “hepatitis” simply means inflammation of the liver, but the causes of hepatitis vary widely. Alcohol, medications, autoimmune disease, toxins, and several different viruses can inflame the liver. Hepatitis A is different from Hepatitis B and Hepatitis C because it does not usually become chronic. A person infected with HAV generally either clears the virus and recovers or, in uncommon severe cases, suffers acute liver failure. The infection is therefore usually time-limited, but that does not mean it is trivial. For adults, older persons, people with chronic liver disease, and immunocompromised individuals, Hepatitis A can be severe, prolonged, relapsing, disabling, and occasionally fatal.
HAV is an RNA virus classified as a picornavirus. One of its most important traits is its environmental toughness. Many viruses are fragile outside the body, but Hepatitis A can persist outside a human host for extended periods depending on environmental conditions. It can survive in water, on surfaces, in sewage-contaminated environments, and in or on foods. It is relatively stable under acidic conditions and at cold or frozen temperatures. This helps explain why frozen food products, shellfish, produce, and ready-to-eat foods have all been implicated in outbreaks. Freezing may preserve the virus rather than destroy it. A consumer may assume that a frozen product is safer because bacterial growth is halted, but HAV is not behaving like a multiplying bacterium. It may simply remain present and infectious until the contaminated food is eaten.
The central route of Hepatitis A transmission is fecal-oral spread. That phrase is blunt but essential. HAV is shed in the feces of infected people. If the virus contaminates hands, food, water, utensils, surfaces, or shellfish-growing waters, another person can ingest it. The amount necessary for transmission can be extremely small. This is why handwashing, sanitation, sewage control, shellfish regulation, and vaccination are the pillars of prevention. The virus is not generally spread by coughing, sneezing, or ordinary casual proximity. Instead, it moves through contamination: a food worker who does not wash hands adequately after using the bathroom; a household member caring for an infected child; contaminated water used to wash produce; shellfish harvested from sewage-impacted waters; or close personal and sexual contact involving fecal exposure.
Once HAV is swallowed, it passes through the gastrointestinal tract and ultimately reaches the liver. There it replicates in liver cells and is excreted through bile into the intestines, where it leaves the body in stool. This creates a public-health problem: the highest levels of virus shedding often occur before the person becomes visibly ill. In other words, the period when a person is most infectious may precede the period when the person realizes something is wrong. By the time jaundice, dark urine, nausea, abdominal pain, fever, or fatigue appear, the infected person may already have exposed household contacts, sexual partners, restaurant patrons, co-workers, or others.
The incubation period of Hepatitis A is unusually long compared with many bacterial foodborne illnesses. Symptoms typically appear about four weeks after exposure, but the range is broad—roughly two to seven weeks. This long delay makes outbreak investigation difficult. A person sick today may have eaten the contaminated food a month ago. They may not remember the meal, the restaurant, the shellfish dish, the grocery item, or the event where exposure occurred. Investigators must often reconstruct weeks of food history, travel history, household contacts, and restaurant exposures. When the vehicle is a frozen imported product with a long shelf life, the problem becomes even harder because the same contaminated lot may remain in freezers and continue to be served or sold.
The symptoms of Hepatitis A can range from none at all to severe liver disease. Young children are often asymptomatic or mildly symptomatic, which means they may spread the virus without being recognized as cases. Adults are much more likely to become visibly ill. Typical symptoms include fatigue, fever, loss of appetite, nausea, vomiting, abdominal discomfort, dark urine, pale or clay-colored stools, joint pain, and jaundice. Jaundice—the yellowing of the skin and eyes—occurs when the inflamed liver cannot process bilirubin normally. Many patients describe profound fatigue, sometimes lasting weeks or months. For people whose work requires physical energy, concentration, travel, or food handling, Hepatitis A can become a major disruption even when it does not become life-threatening.
Most people recover fully from Hepatitis A and then have long-lasting immunity. That is one of the virus’s distinctive features: it generally does not establish a chronic carrier state. This contrasts sharply with Hepatitis B and C, which can become chronic and cause cirrhosis, liver cancer, and long-term liver failure. Hepatitis A is usually acute, but acute does not mean mild. A patient can be hospitalized for dehydration, severe vomiting, abnormal liver enzymes, coagulopathy, or signs of liver failure. Some patients experience prolonged or relapsing disease, with symptoms recurring after apparent improvement. Rarely, HAV causes fulminant hepatitis, a rapid and severe liver failure that can require transplant or result in death.
The severity of Hepatitis A is strongly influenced by age and underlying health. Children under six often have mild or unrecognized infection. Older children and adults are more likely to have symptoms, and older adults are more likely to have severe outcomes. People with chronic liver disease, including chronic Hepatitis B or C, fatty liver disease, cirrhosis, or alcohol-related liver disease, face greater risk because their liver has less reserve. When HAV inflames an already compromised liver, the consequences can be much more serious. This is why public-health authorities often emphasize vaccination for people with chronic liver disease and others at increased risk.
Foodborne Hepatitis A outbreaks occupy a special place in outbreak investigation because the virus has no smell, taste, or visible warning sign. Contaminated food may look completely normal. HAV does not necessarily spoil food. It does not make shellfish smell bad, discolor produce, or change the appearance of a frozen product. A beautifully prepared ceviche, salad, berry dessert, or ready-to-eat sandwich can transmit the virus if contamination occurred at the source, during processing, through sewage-contaminated water, or by an infected food handler. This invisibility is one reason foodborne HAV outbreaks can be shocking to consumers: the food may appear fresh, carefully prepared, and safe.
Shellfish are a particularly important vehicle for HAV because of how they feed. Clams, oysters, mussels, and similar shellfish filter large volumes of water. If the water contains human sewage or fecal contamination, viruses can concentrate in the tissues of the shellfish. This biological concentration is different from ordinary surface contamination. A contaminated clam may contain virus internally, not merely on its exterior. Eating raw or lightly cooked shellfish therefore carries special risk. Acidic preparations such as ceviche may change texture and flavor but should not be assumed to reliably inactivate HAV. The fact that shellfish may be imported, frozen, repacked, distributed through multiple wholesalers, and served in restaurants adds layers of traceback complexity.
Hepatitis A also spreads efficiently through person-to-person contact. Household transmission can occur when family members share bathrooms, prepare food, change diapers, or care for someone who is ill. Sexual transmission can occur, particularly through practices involving oral-anal contact. Transmission has also occurred in outbreaks among people experiencing homelessness and people who use drugs, where barriers to sanitation, handwashing, vaccination, and stable medical care can intensify spread. These outbreaks show that Hepatitis A is not solely a foodborne disease. It is a human disease that exploits weaknesses in hygiene, vaccination coverage, sanitation, and social infrastructure.
Vaccination is the most effective prevention tool. Hepatitis A vaccines are highly effective and are used both for routine prevention and, in certain circumstances, after exposure. In the United States, Hepatitis A vaccination is recommended for children and for various groups at increased risk of infection or severe disease. Vaccination is especially important for international travelers to areas where HAV is more common, people with chronic liver disease, certain occupational groups, people experiencing homelessness, people who use drugs, men who have sex with men, and others identified by public-health guidance. In outbreak settings, rapid vaccination of exposed or at-risk groups can reduce further transmission.
Post-exposure prophylaxis is another distinctive part of Hepatitis A control. Because the incubation period is long, there is sometimes a short window after exposure when vaccination or immune globulin may prevent illness or reduce severity. Public-health authorities generally focus on whether exposure occurred within the prior two weeks. That creates a race against time. When a restaurant exposure is discovered, officials must identify dates, notify patrons, determine who is already immune, assess risk factors, and recommend vaccination or immune globulin where appropriate. Delayed recognition can narrow or eliminate that opportunity.
Diagnosis requires laboratory testing. Clinicians cannot reliably distinguish Hepatitis A from other forms of viral hepatitis based only on symptoms. Blood tests are used to identify acute HAV infection, usually by detecting IgM antibody to HAV. Liver enzymes, bilirubin, and clotting studies may help assess severity. In outbreak investigations, molecular methods can sometimes help determine whether cases are genetically linked. This is particularly useful when multiple patients are scattered across jurisdictions and investigators need to know whether they share a common source.
Treatment is supportive because there is no specific antiviral cure for Hepatitis A. Patients are generally advised to rest, maintain hydration and nutrition, avoid alcohol, and avoid medications or supplements that may stress the liver unless approved by a healthcare provider. Severe cases may require hospitalization. Monitoring is especially important for patients with signs of liver dysfunction, confusion, bleeding problems, persistent vomiting, dehydration, or very high liver enzyme abnormalities. The absence of a curative antiviral drug makes prevention—vaccination, sanitation, safe sourcing, hand hygiene, and rapid outbreak response—especially important.
Food businesses have a major role in preventing HAV spread. Restaurants and food retailers should buy shellfish only from approved, traceable, certified sources. Shellfish tags, invoices, import records, and supplier information matter because traceback can determine whether a contaminated product is still in commerce. Food workers should follow strict handwashing rules, stay home when ill, and comply with public-health exclusion rules if diagnosed with Hepatitis A. Ready-to-eat foods deserve particular care because they may not receive a cooking step before consumption. In the case of shellfish, raw or undercooked service should be treated as inherently higher risk.
Consumers also have a role, though many risks are beyond ordinary consumer control. Vaccination is the most reliable personal protection. Consumers can reduce risk by avoiding raw or undercooked shellfish, especially if they are older, pregnant, immunocompromised, or have liver disease. They can ask restaurants about shellfish sourcing, pay attention to recall notices, and discard products identified in public-health alerts. However, it is unrealistic to place the entire burden on consumers. Hepatitis A prevention depends heavily on upstream controls: safe sewage disposal, approved growing waters, lawful importation, proper refrigeration and documentation, sanitary processing, and effective regulatory oversight.
The Outbreak of HAV Linked to Imported Concha Negra Blood Clams
The recent outbreak associated with imported concha negra blood clams illustrates many of these principles. According to the attached New Jersey Department of Health notice circulated through the Interstate Shellfish Sanitation Conference, New Jersey was notified of a cluster of Hepatitis A cases in New York. The illnesses occurred between August 2025 and February 2026 and were associated with consumption of clam ceviche made from fresh frozen blood clams, also known as black clams, black conch, or concha negra. The clams were reportedly illegally imported from Ecuador. The notice stated that no Hepatitis A cases associated with the product had been identified in New Jersey at the time of the release.
The same notice described traceback efforts involving NJDOH, New York shellfish authorities, and the U.S. Food and Drug Administration. The fresh frozen blood clams were labeled as concha negra and had been shipped to a New York dealer from a New Jersey dealer/importer, then distributed to numerous wholesale and retail establishments in New York and New Jersey, with the possibility of further distribution. The New Jersey shellfish dealer identified in traceback contacted customers and recalled distributed product, while investigators continued working to identify any additional importers and wholesale distributors.
Public-health officials also focused on locating and removing product from commerce. NJDOH asked local and county health departments to look for packaged fresh frozen concha negra from Ecuador during routine inspections. If found, inspectors were asked to report establishment and supplier information and arrange for voluntary destruction or return to the supplier for destruction because the product was from an unapproved source. The package described in the release included the words “La Serranita,” “Concha Negra,” “Shell Meat,” “Fresh Frozen,” and “Net Weight 16 oz (454 g).”
FDA later issued a safety alert advising restaurants, retailers, and consumers not to eat, serve, or sell La Serranita-brand concha negra fresh frozen shell meat from Ecuador because it may be contaminated with Hepatitis A virus. FDA reported distribution to restaurants and retailers in several states and warned that the product may have been further distributed. The agency also emphasized that food contaminated with HAV may look, smell, and taste normal. That warning captures the central danger of Hepatitis A in food: the virus announces itself only after incubation, illness, laboratory diagnosis, and epidemiologic investigation. By then, the contaminated product may have moved through a complex distribution chain and reached consumers who had no way to detect the hazard on their own.
The concha negra outbreak is therefore more than a shellfish recall. It is a case study in the unusual behavior of Hepatitis A. A human virus likely associated with fecal contamination can persist in frozen shellfish, survive long enough to be distributed across jurisdictions, be consumed in a raw or lightly prepared dish such as ceviche, and cause illnesses weeks later. The long incubation period obscures the source, the product’s normal appearance masks the danger, and the shellfish supply chain complicates traceback. The lesson is the same one Hepatitis A has taught for decades: vaccination, sanitation, lawful sourcing, shellfish controls, and rapid public-health investigation are not optional safeguards. They are the defenses that stand between a microscopic virus and a preventable outbreak of liver disease.
