An outbreak of listeria has led to the deaths of three adults in Washington.
Two others have been hospitalized. A common food source has not been identified as the cause.
“The Washington State Department of Health, Tacoma-Pierce County Health Department and Thurston County Public Health and Social Services are investigating a cluster of illness in five adults over 60 years of age who developed severe infections with Listeria monocytogenes (listeriosis),” the state health agency said in a statement on July 21. “All five had compromised immune systems and three of the individuals have died. Genetic fingerprinting results (whole genome sequencing) indicate they likely have the same source of infection.”
The five infected people – two women and three men – became ill between February 27 and June 30, 2023. Four of the cases were recorded in Pierce County. The other was reported in Thurston County. Health officials in both counties interviewed the patients and their families in an effort to “help identify any common exposures.”
The Centers for Disease Control and Prevention estimates 1,600 people contract listeriosis each year, most commonly after eating contaminated food. Pregnant women, newborns, adults over the age of 65 and people with weakened immune systems are at higher risk of becoming ill. In particular, pregnant women are reported to be 18 times more likely to get listeriosis than the average healthy adult.
The bacteria become an invasive illness once it has spread beyond the gut, typically within two weeks of eating contaminated food. Symptoms included fever, muscle aches, and fatigue. Non-pregnant infected people may also experience loss of balance, confusion, headache, stiff neck, and seizures.
The illness is diagnosed with a bacterial culture from body tissue or fluid and treated with antibiotics.
The CDC recorded five outbreaks of listeriosis in 2022, four in 2021, two in 2020, and three in 2019.
According to the Food and Drug Administration:
The bacteria are able to live in a wide range of conditions and environments—they can tolerate both acidic and salty conditions, both high and low temperatures, and a fairly low moisture content. These characteristics allow L. monocytogenes to survive a long time in a variety of food products and food processing plants. Because the bacteria can multiply and persist in food processing plants for years—even more than 10 years in one documented case—L. monocytogenes is especially hard to control and can result in intermittent contamination of food.
Unlike most bacteria, L. monocytogenes can grow and multiply at low temperatures, making the bacteria a potential problem even in properly refrigerated food. One study also found a relatively high percentage of frozen raw beef products contaminated with L. monocytogenes. This finding highlights the ability of the bacteria to thrive in cold environments.
The agency notes listeria typically contaminates raw meat, refrigerated pates, ready-to-eat smoked seafood and raw seafood, soft cheeses made with unpasteurized milk, unpasteurized milk and milk products, and melons.
