RECENT REPORTS OF Listeria monocytogenes (Listeria) contamination in ice cream and other food products have renewed interest in protecting the food supply and safeguarding the public against this life-threatening pathogen.1Listeria is a bacterium normally found in soil and water. It's also found in cattle and poultry without making the animals ill.2
Listeriosis occurs when a person consumes food or liquids contaminated with Listeria. Every year in the United States, more than 1,600 people become ill with listeriosis, with 1,400 related hospitalizations.3,4 Listeriosis is the third leading cause of death from food poisoning, resulting in 250 annual deaths.3,4
Foods that have a high risk of Listeria contamination include:
- uncooked vegetables and meats
- raw (unpasteurized) milk and cheeses
- food made from unpasteurized milk
- raw sprouts
- cooked or processed foods (such as certain soft cheeses, ready-to-eat meats and hot dogs, and smoked seafood).2,5
Who's at risk?
Older adults, pregnant women, newborns, and people with weakened immune systems are at highest risk for becoming ill from listeriosis. Rarely, people without these risk factors also become ill.5
Approximately 58% of Listeria infections affect adults age 65 and older.6 This age group is four times more likely than the general public to become infected.6
About 14% of Listeria infections occur during pregnancy, which can result in premature delivery, miscarriage, stillbirth, and additional health problems for the neonate.7 Pregnant women are about 10 times more likely than the general population to become ill from listeriosis.6 Pregnant Hispanic women have an even higher risk and are about 24 times more likely than the general population to become ill.6
Individuals at high risk for contracting listeriosis due to immunocompromise include those who have cancer, liver, or kidney disease; diabetes; alcoholism; and HIV/AIDS, as well as those being treated with steroids, chemotherapy, or radiation.6
Diagnosing and treating listeriosis
The incubation period for Listeria ranges from 3 to 70 days, with illness lasting from days to weeks. Signs and symptoms of listeriosis include fever, nuchal rigidity, confusion, weakness, and vomiting, which is sometimes preceded by diarrhea.2 The prolonged incubation period makes it difficult for an individual to identify foods that may have contributed to the illness. The clinical diagnosis is confirmed after identifying the pathogen from blood, cerebrospinal fluid, amniotic fluid, or placenta; culturing stool specimens isn't recommended.8 Standard precautions are used while caring for patients with listeriosis.
Treatment of listeria infection varies, depending on the severity of the signs and symptoms. Most individuals with mild symptoms require no treatment.9 Gastroenteritis may not be routinely treated unless a susceptible host (such as a pregnant woman) is involved; in that case, oral amoxicillin or trimethoprim/sulfamethoxazole is recommended.10 For severe illness, I.V. ampicillin, with possible gentamicin for synergy, is administered.10 No vaccine currently exists to prevent listeriosis.
Listeria infections must be reported to the department of health by the microbiology lab performing the testing. In 2014, 769 cases of listeriosis were reported in the United States.11 Investigators use a standard questionnaire about high-risk foods when interviewing patients to determine the potential contaminated food source.
Listeria is killed by cooking foods at their recommended temperature, pasteurization, and proper sanitation of food contact surfaces. This organism has been found growing even in a cold refrigerator.2 Listeria can live for years in a food processing factory if sanitation breakdowns occur.12
To prevent listeriosis and other foodborne illnesses, advise patients to:
- thoroughly cook raw meat, poultry, and seafood to a safe internal temperature.
- store refrigerated and frozen foods at proper temperatures.
- properly wash and rinse raw vegetables under running tap water before eating.
- wash hands with soap and water before and after handling foods.
- eat only pasteurized dairy products.
- sanitize all food contact surfaces (cutting boards, countertops) and equipment/utensils immediately after use.
- keep uncooked meats, poultry, and seafood separate from vegetables, fruits, cooked foods, and ready-to-eat foods.
- heat hot dogs, cold cuts, and deli meats before eating them (for those in high-risk groups).
- discard food products that have passed their “Use By” dates.2,13