A multistate salmonella outbreak may be linked to oysters. What people should know

By Katia Hetter, CNN

(CNN) — A multistate outbreak of salmonella infections likely linked to raw oysters has sickened more than 60 people across 22 states, according to a US Centers for Disease Control and Prevention health advisory.

Health officials are working to identify the source of those contaminated raw oysters, the advisory issued December 23 said.

What is salmonella, and how does it make people sick? How do oysters become contaminated, and is it ever safe to eat them? What should you know if oysters are on the menu for upcoming social gatherings? Which groups of people are most vulnerable to severe illness? What other types of seafood can carry similar risks, and how can you reduce your chances of getting sick?

To help with these questions, I turned to CNN wellness expert Dr. Leana Wen. Wen is an emergency physician and clinical associate professor at George Washington University. She previously was Baltimore’s health commissioner, with responsibilities that included overseeing food safety.

CNN: What is salmonella, and how does it make people sick?

Dr. Leana Wen: Salmonella is a group of bacteria that causes one of the most common foodborne infections in the United States. People usually become infected after eating food contaminated with the bacteria. Once inside the body, salmonella triggers inflammation that leads to gastrointestinal illness.

Salmonella is often associated with undercooked poultry, eggs and contaminated produce, but it can also be found in seafood, including oysters. Because the bacteria are invisible and do not change the smell or taste of food, people typically have no warning that what they are eating may make them sick.

CNN: What kind of symptoms do people experience, and how is the illness treated?

Wen: Symptoms of salmonella infection usually begin within six hours to several days after exposure. Common symptoms include diarrhea, stomach cramps, fever, nausea and vomiting. Many people also feel fatigued and dehydrated. In most healthy adults, symptoms last four to seven days and resolve on their own without specific treatment.

Care is primarily supportive in nature. The most important step is staying well-hydrated, especially if diarrhea is frequent. Oral rehydration solutions can help replace lost fluids and electrolytes. Over-the-counter fever reducers such as acetaminophen or ibuprofen can help manage discomfort as long as they are used appropriately and do not exceed recommended amounts. Antibiotics are not recommended except for people with severe illness or at high risk for complications because they may prolong the time someone carries the bacteria.

CNN: Who is most vulnerable to severe illness from salmonella?

Wen: While most people recover quickly from salmonella infection, certain groups are at much higher risk for severe disease. These include adults over age 65, infants and young children, pregnant individuals, and anyone with a weakened immune system due to conditions such as cancer, diabetes, or kidney disease or medications that suppress immunity.

In these vulnerable people, salmonella is more likely to spread beyond the intestines into the bloodstream, leading to serious infections that require hospitalization and antibiotic treatment. If you’re pregnant, infection can also increase the risk of fetal complications. Because of these risks, people in high-risk groups should avoid eating raw oysters altogether.

CNN: How do oysters become contaminated, and is it ever safe to eat them?

Wen: Oysters are filter feeders, meaning they pull in large volumes of water to extract nutrients. If the water where they are harvested is contaminated with bacteria from sewage runoff, those pathogens can accumulate inside the oyster. Unlike some other foods, oysters are often eaten raw or lightly cooked, which means there isn’t the heating step to kill bacteria.

Cooking oysters thoroughly greatly reduces the risk of infection because heat kills salmonella and other pathogens. Eating oysters raw always carries some degree of risk, even when they are harvested from approved waters and handled according to regulations. Testing and monitoring reduce risk but cannot eliminate it entirely. That is why health officials consistently warn that raw or undercooked oysters are never completely safe to eat.

CNN: What should you know if oysters are on the menu for social gatherings?

Wen: If oysters are being served, it’s important to know whether they are raw or fully cooked. Cooked oysters should be steaming hot and prepared in a way that ensures they reach safe internal temperatures. Oysters in the shell should be steamed for four to nine minutes in a steamer that’s already steaming. Shucked oysters should be boiled, broiled or fried for at least three minutes.

If you are hosting, consider offering cooked seafood options instead of raw oysters or clearly labeling which items are raw or undercooked so guests can make informed choices. Avoid cross contamination by keeping raw seafood separate from cooked foods and using different utensils.

In addition, if oysters are served raw, they should be kept cold until serving. Discard them after they have been left out for more than two hours, or one hour if the environment is very warm.

CNN: Does using hot sauce or lime or lemon juice kill salmonella?

Wen: No. The only way to be sure to kill salmonella and other pathogens is through cooking until the internal temperature reaches at least 145 degrees Fahrenheit (about 63 degrees Celsius) for at least 15 seconds.

CNN: What other types of seafood can carry similar risks?

Wen: Raw or undercooked seafood can carry a variety of bacteria and viruses, not just salmonella. Raw shellfish such as clams, mussels and scallops can contain pathogens picked up from contaminated water. Certain fish may carry parasites if eaten raw or undercooked. And seafood products can pose risks if not handled or stored properly.

Beyond seafood, similar food safety principles apply to other high-risk foods. Unpasteurized dairy products, undercooked meat and poultry, and raw eggs are common sources of foodborne illness. The key theme across these foods is that pathogens are more likely to survive when foods are eaten raw or improperly cooked.

CNN: How can people reduce their chances of getting sick from salmonella?

Wen: The most effective way to reduce risk is to avoid raw or undercooked seafood, including oysters. Good-food handling practices also matter. Wash hands with soap and water before and after handling raw seafood. Clean and sanitize cutting boards, knives and surfaces that come into contact with raw foods. Keep raw seafood and meat separate from cooked and ready-to-eat foods to prevent cross contamination. Refrigerate promptly and never leave perishable foods out for extended periods.

For people who choose to eat raw oysters despite the risks, it is especially important to pay attention to public health advisories and recalls. If you experience symptoms such as bloody diarrhea, high fever or so much vomiting you can’t keep fluids down, seek medical care, especially if you are in a higher-risk group.

My takeaway is that seafood can be part of a healthy diet, but it needs to be prepared and consumed safely. During outbreaks like this one, extra caution is warranted. Making informed choices now can help ensure that holiday celebrations end with good memories rather than an unexpected illness.

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