Listeriosis

Listeriosis is an infection caused by the bacterium Listeria monocytogenes. Outbreaks of this disease are generally related to the ingestion of foods containing large amounts of this bacterium.

It is a relatively rare disease, since its incidence is quite low compared to other diseases associated with foodborne micro-organisms.

However, Listeriosis is of special interest and concern because in its invasive form it is a serious disease, with very high lethality rates (between 10% and 30%). Moreover, Listeria monocytogenes is an opportunistic pathogen that almost always affects the population at risk, while in the general population its infection does not usually lead to the development of the disease.

 

Risk groups: – Pregnant women – Newborns – People with weakened defences: o Chronically ill people o Elderly people o Persons undergoing certain medical treatments · The probability of contracting the disease is about 20 times higher in pregnant women than in other healthy adults. · Patients with HIV/AIDS are 300 times more likely to suffer from listeriosis than people with a normal immune system. · People over 65 years of age represent 62% of those affected, with a mortality rate of 19%.

Incidence of Listeriosis

The rate of human Listeriosis in the European Union in 2019 has a Prevalence of 0.46 cases per 100,000 people (EFSA 2020).

The EU trend of confirmed cases of Listeriosis has remained stable over the last three years (2621 cases in 2019).

 

 

Trend in reported confirmed human cases of listeriosis in the EU/EEA, by month, 2009– 2019

On the other hand, global data (WHO 2018) show low prevalence (0.01-0.1 cases per 100,000 people) but very high mortality (20 – 30%) in susceptible individuals.

Infective dose

The infective dose is not determined and depends on factors such as strain, host susceptibility (immune status, age,…) or the food matrix involved.

According to a model used by EFSA, 92% of cases of invasive Listeriosis would be attributable to doses above 100,000 colony forming units (CFU) per serving.

Therefore, assuming an average serving size of 50 g, this would correspond to a concentration of Listeria monocytogenes above 2,000 CFU/g at the time of consumption.

However, it is likely that less than 1,000 CFU/g can cause disease in susceptible individuals.

Incubation period

Gastroenteritis caused by Listeria monocytogenes has a relatively short incubation period, ranging from a few hours to 2 or 3 days.

On the other hand, in the severe, invasive form of the disease, the incubation period is usually 1 to 2 weeks, but can range from a few days to 3 months.

This prolonged incubation period makes it difficult to identify the food at the origin of the infection.

Symptoms of Listeriosis

Listeriosis causes two forms of disease in humans:

• Non-invasive: a mild form that affects mostly healthy people. Symptoms are diarrhoea, fever, headache and muscle aches.
• Invasive:it is more severe and affects high-risk groups. It is characterised by severe symptoms and a high mortality rate (20-30%). Symptoms include fever, muscle aches, septicemia and meningitis.

Pregnant women may experience mild flu-like symptoms (fever, fatigue and muscle aches) but Listeria can be transmitted to the fetus causing miscarriage, stillbirth, premature delivery or life-threatening infections in the newborn (bacteremia and meningitis). One third of confirmed cases of maternal-fetal Listeria monocytogenes infections result in miscarriage or fetal death.

Treatment for Listeriosis

Listeriosis can be treated if diagnosed early. Antibiotics are used to treat severe symptoms such as meningitis. When infection occurs during pregnancy, immediate administration of antibiotics prevents infection of the fetus or newborn.

Transmission of Listeriosis

Listeria monocytogenes can be transmitted to humans by vertical (mother-child transmission through the placenta), zoonotic and/or nosocomial routes. Currently, 99% of cases of human Listeriosis are foodborne through the consumption of food of animal origin (meat, fish, milk, etc.) contaminated with pathogens.

How to prevent listeriosis?

In general, the prevention of Listeriosis is similar to the prevention of other foodborne diseases and, for this reason, it is important to follow the five keys to food safety defined by WHO:

1. Maintain
2. Separate raw and cooked foods.
3. Cook completely:

• At-risk groups should be aware of the foods that present risk and avoid consumption or consume them after heat treatment at more than 70°C.

4. Keep food at safe temperatures:

• Always keep the refrigerator temperature below 4°C (39°F).

5. Use water and safe raw materials:

• Respect the expiry dates of foods kept refrigerated.

In addition, people in high-risk groups should:

• Avoid consuming dairy products made with unpasteurised milk; cold cuts and ready-to-eat meat products such as sausages, hams, pates and spreads, as well as cold-smoked seafood (such as smoked salmon);
• Respect the shelf life and storage temperature written on the labels of ready-to-eat foods;
• Cooking before eating is another very effective way to kill bacteria.

Conclusiones

• Listeriosis is a relatively rare disease but its invasive form is a serious disease, with high fatality rates especially in at-risk groups.
• Its infective dose is not completely determined and its incubation period can vary from a few hours to almost 3 months.
• To prevent the disease, we should be aware of the foods that present risk and follow the five keys to food safety proposed by the WHO.

PROQUIMIA, through its wide range of detergent and disinfectant products for surfaces and hands, develops customised Cleaning and Disinfection plans for each process and installation, in order to guarantee the maximum hygienic conditions of food.

Sources

• ACSA bulletin brief no.9 may-june 2018. 2018. https://bit.ly/2Sc0jt3
• Published in the EU zoonoses report “One Health” 2019. 2021. https://bit.ly/3vyuFqS
• EFSA Journal. The European Union One Health 2018 Zoonoses Report. 2019. https://bit.ly/34XukE8
• EFSA Journal. The European Union One Health 2019 Zoonoses Report. 2021. https://bit.ly/3wIRPw0
• One Health Report on Zoonoses in Europe 2019. 2021. https://bit.ly/3iMRdl3
• Listeria. https://bit.ly/2HFPZaJ
• Listeriosis. 2018. https://bit.ly/3xkCfGW

AUTHOR: Agustí Capdevila