Listeria Facts, Outbreaks, Symptoms, and All You Need To Know About This Foodborne Disease

History of Listeria

Listeria was first discovered in England in 1926 by E.G.D. Murray and his colleagues during a laboratory investigation of sudden deaths in young rabbits [4]. However, it was identified as a severe source of foodborne illness only in 1986 [5]. Listeriosis is the disease caused by eating food contaminated with listeria monocytogenes [6,7].

The pathogen’s name changed several times until 1940 when it was officially called listeria after Joseph Lister, the ‘father of modern surgery’ who devised a way to reduce infections during surgery.

Epidemiology and Prominent Outbreaks of Listeriosis and Listeria Infection

The most recent notable outbreak was in South Africa from January 2017 to July 2018. The listeria outbreak in South Africa was caused by contaminated polony. Polony (or Bologna) is a sausage made of pork, beef, or other meats. There were 1060 lab-confirmed cases of Listeriosis in South Africa, with 216 reported deaths [3].

Another notable listeria outbreak occurred from August 2021 to January 2022 in the United States and was linked to packaged greens. In total, 18 people fell sick, 16 of them were hospitalized, and there were three deaths. The Centers for Disease Control and Prevention (CDC) declared the outbreak over on April 4, 2022. You can access the case count map on GIDEON. On average, there are around 1,600 reported cases of listeria infections, with 260 people dying from it each year [6].

How is it Spread? What Does Food Have to Do with It?

Listeriosis is usually transmitted by eating food contaminated with Listeria monocytogenes. People most at risk are those with a weak immune system (including those undergoing treatment for cancer, HIV, and other immune deficiency diseases), older adults, pregnant women, and infants [5,6,8].

Pregnant women are 20 times more likely to be infected than normal adults [6]. Listeriosis can be transmitted from a woman’s body to the fetus through the placenta during pregnancy, resulting in a miscarriage or stillbirth [7,8]. Sometimes, babies may be born with severe systemic infections [9]. Additionally, people with HIV are 300 times more likely to contract listeriosis than healthy individuals [6].

Biology of the Disease

Listeria monocytogenes can be found in soil, water, and animals [10]. Raw and unpasteurized milk, cheeses, and other dairy products are the common sources of listeria in our food [10]. Raw and processed vegetables are also usual suspects.

Fruit and vegetables can pick up bacteria from the soil [11]. Since listeriosis is a food-borne disease, the primary site of entry for the bacteria in the host is the gastrointestinal tract [7]. For mild illness (gastroenteritis), the infection usually begins 20 hours after eating the contaminated food. Whereas in the case of a severe illness, the incubation period is around 20 to 30 days [7].

Listeria spreads by invading the macrophages and tissue cells of infected persons. Once the bacteria enter the host’s living cells, they exit the phagosomal compartment and enter the cytoplasm. This is how the bacteria travel from one cell to another [12].

The bacteria spread through the small intestine mucus membrane and permeate the lymph nodes and blood cells. Listeria’s main target is the liver — where the bacteria multiply. As they proliferate, they cause prolonged infection in the bloodstream, particularly in people with a weak immune system [12].

Symptoms

Symptoms of listeria can take a few days or even 90 days to show up, but on average, the incubation period is one to two weeks [1]. According to the CDC, the symptoms experienced by pregnant women infected by listeriosis include:

• Fever
• Flu-like symptoms like fatigue and muscle pain [13].

Signs of listeria infections in people other than pregnant women include:

• Fever
• Muscle aches
• Headaches
• Stiff neck
• Confusion
• Loss of balance
• Convulsions [13]

The three commonly observed clinical manifestations of listeriosis include:

• Infection in the bloodstream
• Infection of the central nervous system
• Maternal-fetal listeriosis [2]

Diagnosis

Diagnosis of listeria infections is complicated because of its incubation period and different clinical manifestations.

When the listeria bacteria is suspected of being the source of infection, blood samples are collected and used as a medium to culture the bacteria. It usually takes 24 to 48 hours for the bacteria to grow.

Depending on the type of clinical manifestation, different mediums like joint, peritoneal, and cerebrospinal fluids can be used to culture the organism [2].

Treatment

Since listeriosis is associated with a high mortality rate, medical professionals will need to start treatment early [2]. Most people with mild symptoms of listeria, do not require treatment and often get better on their own. Serious illnesses require hospital care, and about one in five infected people die [14]. People diagnosed with a listeria infection are usually given antibiotics like ampicillin. In some cases, ampicillin is combined with gentamicin [14].

The dosages at which these antibiotics are administered vary depending on the severity level. The duration of the treatment also varies depending on the level of severity and the individual. Depending on the clinical manifestations of the patients undergoing the treatment, the doctor can take a call on whether to prolong the treatment after the first two weeks or not [3].

Prevention

Prevention is always better than cure. But in order to prevent ourselves and our loved ones from listeriosis, we need to be aware of how the infection spreads. In the US, the spread of listeriosis is linked to unpasteurized milk and cheeses, ice creams, raw or processed vegetables and fruits, raw or undercooked poultry, raw fish, and other seafood. Sometimes, even cooked food items can get contaminated during packaging [15].

Storing food contaminated with listeria monocytogenes in a refrigerator for an extended period of time causes further contamination [15]. Setting the temperature of the refrigerator to 40℉ can help slow down bacterial multiplication [14,15]. Here are some preventive measures to protect against listeriosis:

• Regular cleaning and sanitizing of shelves and walls inside the refrigerator
• Regular cleaning and sanitizing of chopping boards and other utensils used to store or prepare food
• Regular cleaning and sanitizing of the shelves used where the utensils are kept
• Drying utensils before putting them back onto their shelves
• Wash hands with soap before handling any food items
• Wash hands with soap after handling pet food and clean dishes as soon as the pets are done eating
• Heating certain food items like deli meals and hot dogs until steaming hot before eating
• Refrigerate leftovers within two hours to avoid any sort of contamination
• Avoid raw or uncooked meat, and raw or unpasteurized dairy products (mostly advisable for pregnant women and people with a weak immune system) [14, 15]