CDC Investigates Hepatitis A Outbreak Potentially Linked to Imported Frozen Black Clams

A multistate outbreak of hepatitis A is being investigated by U.S. health authorities after dozens of people became sick and many required hospitalization. Federal officials say epidemiological evidence points to a possible connection with imported frozen black clams, particularly products that were eaten raw or undercooked.

As of September 17, 2026, the Centers for Disease Control and Prevention (CDC) had identified 37 illnesses across four states. Thirty of those patients, or about 81 percent, had been hospitalized. No deaths had been reported. The affected states are Massachusetts, Minnesota, New York, and Pennsylvania.

Health officials are continuing to investigate the outbreak and trace potentially contaminated products. The CDC has also warned that the actual number of infections could be higher because some people with hepatitis A may recover without seeking medical attention or may not be tested for the virus.

What the CDC Has Found

The investigation began in May 2026, when the CDC, the U.S. Food and Drug Administration (FDA), and state and local health authorities started looking into a possible multistate hepatitis A outbreak associated with frozen clams. Investigators have been examining the foods that infected people consumed before becoming ill.

The CDC says people were asked about foods they ate during the 15 to 50 days before they developed symptoms. Among those interviewed, 77 percent said they had eaten ceviche, which can contain raw fish or shellfish marinated in citrus juice.

Another 76 percent reported eating raw or undercooked shellfish, while 47 percent reported eating raw or undercooked conchas negras, commonly known as black clams.

These figures were higher than consumption levels reported in a CDC FoodNet population survey. According to federal investigators, the difference provides evidence that raw or undercooked clams may have played a role in the outbreak.

However, the investigation remains ongoing. The CDC describes the outbreak as potentially linked to frozen clams and says traceback work is continuing to determine the source or sources of the products consumed by people who became sick.

Which Clam Products Are Involved?

The FDA has issued a safety alert concerning La Serranita-brand concha negra, or black shell, shell meat imported from Ecuador.

The affected product is described by the FDA as fresh frozen shell meat sold in 16-ounce plastic packages. The agency says the product was distributed to restaurants and retailers in Connecticut, Massachusetts, New Jersey, New York, Ohio, and Pennsylvania. The FDA also warns that the product may have been distributed more widely.

Consumers, restaurants, retailers, and food-service businesses have been advised not to eat, sell, or serve the affected product.

The FDA recommends that potentially contaminated products be discarded or that businesses contact their distributors to arrange for destruction. Anyone who handled the product should also carefully clean and sanitize surfaces and containers that may have come into contact with it.

One important point is that contaminated food does not necessarily look, smell, or taste unusual. This means consumers cannot determine whether a particular product is safe simply by inspecting it.

Why Raw Shellfish Can Present a Risk

Shellfish can become contaminated with viruses and bacteria because they filter water as they feed. If the surrounding water is contaminated, microorganisms can accumulate inside the shellfish.

Hepatitis A is caused by the hepatitis A virus, or HAV. The infection primarily affects the liver and can spread when someone consumes food or water contaminated with the virus. It can also spread through close personal contact with an infected person.

Eating shellfish raw or only partially cooked can increase the risk of exposure when the product is contaminated. Cooking food thoroughly can reduce the risk associated with many foodborne pathogens, although consumers should always follow official food safety instructions and product-specific recalls.

The current investigation does not mean that all clams or all shellfish are contaminated. Rather, federal officials are focusing on specific products and possible sources associated with the outbreak.

Symptoms Can Take Weeks to Appear

One reason hepatitis A outbreaks can be difficult to identify quickly is the delay between exposure and illness.

According to the CDC, symptoms generally appear between two and seven weeks after exposure. The FDA similarly notes that illness can occur 15 to 50 days after consuming contaminated food or water.

Symptoms can include fatigue, fever, loss of appetite, nausea, vomiting, abdominal pain, diarrhea, joint pain, dark urine, pale or clay-colored stools, and jaundice.

Jaundice causes the skin or whites of the eyes to turn yellow and is one of the more recognizable signs of hepatitis A.

Not everyone infected with hepatitis A develops noticeable symptoms. Adults are more likely to experience symptoms than young children, according to the CDC. Most people recover from hepatitis A, although illness can last from several weeks to several months.

In uncommon cases, hepatitis A can cause serious complications, including liver failure. Severe illness is more likely among older adults and people with certain underlying liver conditions.

What Consumers Should Do

The CDC recommends that people who have eaten frozen La Serranita-brand concha negra shell meat raw or undercooked within the previous 14 days and who are not vaccinated against hepatitis A contact a local health department or healthcare provider.

Medical professionals can discuss whether post-exposure treatment is appropriate.

People who have potentially consumed the recalled product should not wait for symptoms before seeking advice when they fall within the CDC's recommended exposure window.

Consumers should also check their freezers and refrigerators for the affected product and avoid tasting it to determine whether it is safe. If the product is present, it should be handled according to FDA disposal recommendations.

Restaurants and retailers should similarly check their inventory and follow the FDA's instructions regarding disposal and sanitation.

The Investigation Is Still Underway

Although investigators have identified a strong epidemiological association between the outbreak and consumption of raw or undercooked clams, federal authorities have not indicated that every illness has been conclusively traced to one particular package or supplier.

The CDC says traceback investigations remain underway. Officials are also warning that the outbreak may extend beyond the four states where cases have been identified.

The agency believes additional infections may not yet have been detected because some people recover without medical care, while recently occurring illnesses may take time to be diagnosed and linked to an outbreak.

For consumers, the key message is to pay attention to official recall information and avoid eating the affected La Serranita-brand concha negra product. People who believe they may have been exposed should contact a healthcare professional or local health department, particularly if they are within the CDC's recommended 14-day post-exposure window.

Sources: CDC and FDA.

Disclaimer

This article is provided for general informational purposes and is not medical advice. Information about the outbreak can change as federal and state health authorities continue their investigation. Consumers should rely on the latest guidance from the CDC, FDA, state health departments, and their healthcare professionals for decisions concerning potential exposure, vaccination, treatment, or symptoms.