At least 27 people sickened and 6 dead in latest US listeria outbreak. What you should know

(CNN) — Six people have died due to a multistate outbreak of listeria linked to recalled prepared pasta meals sold at major grocery chains, including Albertsons, Kroger, Sprouts Farmers Market and Trader Joe’s.

The warning by federal health officials noted at least 27 reported cases of infection across 18 states, and health officials said that a pregnant woman lost her fetus after becoming ill.

I wanted to know more about listeria contamination and why it’s dangerous. What symptoms should people watch for, and how is the infection diagnosed and treated? Who is most at risk for severe illness, and what foods are most often linked to outbreaks like this one? And as we head into the holiday season, what can people do to reduce their chances of getting sick from foodborne bacteria?

To help me 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 served as Baltimore’s health commissioner, where her responsibilities included overseeing food safety.

CNN: What is listeria, and why is it dangerous?

Dr. Leana Wen: Listeria monocytogenes is a type of bacteria found in soil, water and certain foods that can cause a serious infection known as listeriosis. Unlike many other foodborne pathogens, listeria can grow at refrigerator temperatures, which means it can survive and multiply in foods that are already cooked or stored cold. It most often contaminates ready-to-eat foods such as deli meats, soft cheeses, smoked fish, unpasteurized dairy products and refrigerated prepared meals.

For most healthy adults, a mild infection may cause only brief flu-like symptoms, but for certain people, including pregnant people, newborns, older adults and those with weakened immune systems, listeriosis can be severe. It can cause bloodstream infections, meningitis, or pregnancy complications like preterm labor, miscarriage and stillbirth. Listeria infection is the third leading cause of death from foodborne infection in the United States, according to the US Centers for Disease Control and Prevention. Each year, about 172 people die from infection.

CNN: What symptoms should people watch for?

Wen: Symptoms of listeriosis often start with fever, chills, muscle aches, nausea or diarrhea. In more serious cases, the infection spreads beyond the gut and can cause severe headache, stiff neck, confusion, seizures and whole-body infection resulting in organ failure. Pregnant patients may experience only mild flu-like symptoms, but the infection can be devastating to a developing fetus.

CNN: How is listeria diagnosed and treated?

Wen: Doctors diagnose listeriosis through laboratory testing, usually by identifying the bacteria in a blood sample, spinal fluid or other body fluid. In mild cases, treatment may not be necessary beyond monitoring symptoms, but in more severe cases, antibiotics are required. Pregnant people, newborns, older adults and immunocompromised individuals may be hospitalized for closer monitoring and supportive care. Early diagnosis and treatment significantly improve outcomes.

CNN: What should consumers do if they have the recalled products at home?

Wen: Anyone who purchased the recalled pasta meals should not eat them, even if they look or smell fine. The bacteria can’t be seen, smelled or tasted. And just because someone else has eaten it and has not gotten sick doesn’t mean that it’s safe for you to eat.

Check your refrigerator and freezer for any recalled brands or packaging, and either return them to the store or throw them away in a sealed plastic bag to prevent cross-contamination. Wash and sanitize any surfaces, shelves or containers that may have come into contact with the recalled products. If you or a family member has eaten one of the recalled foods and developed symptoms consistent with listeriosis, contact your health care provider.

CNN: As we head into the holiday season, what can people do to reduce their chances of getting sick from foodborne bacteria?

Wen: The high-profile outbreaks that make headlines can give the impression that foodborne illnesses mainly come from restaurants or packaged foods purchased in stores. In reality, only a small portion of cases are traced to commercial products; most occur in our own kitchens, where bacteria and viruses can easily spread through everyday handling of food. Practicing careful hygiene and safe cooking habits at home is one of the most effective ways to reduce the risk of infection.

Among all foodborne pathogens, norovirus is the most common cause of gastrointestinal illness in the US. It spreads quickly from person to person and through contaminated food, especially when infected individuals handle meals before or during preparation.

Frequent, thorough handwashing with soap and water is essential, especially before cooking, after using the bathroom and after touching shared surfaces. Anyone with symptoms such as nausea, vomiting, diarrhea or stomach cramps should stay home and avoid preparing or serving food to others until they have been symptom-free for at least two days. This applies not only to norovirus but to other contagious gastrointestinal ailments as well.

Undercooked meat, poultry and seafood are another leading source of foodborne illness, including infections from bacteria such as salmonella, campylobacter and E. coli. Cooking foods to their proper internal temperatures kills these pathogens: Chicken, turkey and other poultry should reach 165 degrees Fahrenheit (74 degrees Celsius); fish should be cooked to 145 F (63 C); and ground meats such as beef or pork should reach at least 160 F (71 C). Using a food thermometer is the most reliable way to ensure these temperatures are met.

Cross-contamination is also a frequent problem. Cutting boards, knives and plates that have been in contact with raw meat, seafood or poultry should never be reused for cooked or ready-to-eat foods unless they have been thoroughly washed in hot, soapy water. Keeping separate utensils and cutting surfaces for raw and cooked foods greatly reduces the risk of spreading bacteria.

Fresh fruits and vegetables should always be washed, even if they’ll be peeled before eating. Rinsing under running water is usually sufficient; avoid using soaps or household cleaners, which can leave residues that are unsafe to consume. For firm produce like melons or cucumbers, using a clean brush can help remove dirt and bacteria from the surface.

Proper storage is another key part of prevention. Perishable foods should be refrigerated within two hours of cooking — or within one hour if the air temperature is above 90 F (32 C). Leftovers should be stored in shallow containers so they cool quickly, and refrigerators should be kept at 40 F (4 C) or lower. Freezers should be set at 0 F (-18 C) or below. Food left out too long provides ideal conditions for bacteria such as listeria and staphylococcus to multiply rapidly.

Avoid unpasteurized milk and dairy products, as well as juices or ciders that have not been pasteurized, since these can contain harmful bacteria. Pregnant people, older adults and anyone with a weakened immune system should be particularly careful to avoid these products, as they carry a higher risk of serious illness.

Finally, pay attention to local and national health advisories. Health departments and the CDC frequently issue alerts when contaminated foods are identified or when outbreaks are detected at local restaurants or grocery chains. Following these updates and checking your kitchen for recalled items can help you act quickly to prevent illness.

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