Around 3,000 listeriosis cases per year in the EU: the “cruel survivor” of cold stores

While the food industry is developing at a rapid pace, a small but tenacious enemy is causing an increasingly serious headache for authorities, laboratories and manufacturers alike. Listeria monocytogenes is not just one of many pathogens: this bacterium multiplies where others die and causes an extremely serious, sometimes fatal disease: around 3,000 cases are registered in the European Union every year – listeriosis is rare, but one of the most serious foodborne infections. The danger is not theoretical: recently in France, an outbreak linked to soft cheeses infected at least 21 people and caused two deaths, while in Hungary, refrigerated foods – such as fish products – had to be recalled from the market several times due to the Listeria risk.

Listeriosis: more than just an upset stomach

The root of the problem lies in the insidiousness of the disease called listeriosis. While the average food poisoning will pass in a few days, Listeria infection can have an incubation period of up to 90 days. In healthy adults, it often causes only flu-like symptoms, but for vulnerable groups – the elderly, pregnant women or patients with weakened immune systems – the outcome can be fatal. The bacteria can cross the blood-brain barrier, causing severe meningitis, and in pregnant women, reaching the fetus, it can cause miscarriage or severe neonatal damage. For this reason, public health experts emphasize that the presence of Listeria in the food chain is treated with an extremely low risk tolerance, so prevention and continuous laboratory monitoring are key.

Authority strictness and domestic experiences

The Hungarian authority, Nébih (National Food Chain Safety Authority), is also paying special attention to the pathogen. The Nébih product recall data are reminiscent of the 2018 European Listeria outbreak, which started in Hungary: several hundred tons of products had to be withdrawn from circulation worldwide due to quick-frozen vegetable mixes produced in a domestic refrigeration plant. This case highlighted that the bacterium’s tenacity is the biggest challenge: it is able to form a biofilm layer and settle in hard-to-clean areas of plants, such as floor drains, from where it can invisibly contaminate finished products.

The Invisible Line: What Happens in the Lab?

In a strict regulatory environment, the role of independent, accredited testing laboratories is crucial because it means real safety for both manufacturers and consumers. But what does a laboratory do behind the scenes, and why does this work require engineering precision?

Laborhírek asked experts from a Budapest testing laboratory how they can fight the insidious survivor. The staff of the microbiological laboratory of Hamilton Hungária Kft. told the professional blog that they are trying to filter out the infection with the combined power of several methods, in synergy if you like, in order to verify the conformity of the products with the lowest possible error rate.

Ready-made food can arrive at the laboratory, but often surface samples from the production environment – ​​so-called swab tests – can also be used. With the help of these, the experts not only check the product, but also the production environment, so the source of the infection can be identified during production.

The most important step in the laboratory then follows: “waking up” the bacteria. Listeria often enters the sample in a damaged state – for example, after cooling or freezing – and is therefore propagated in special enrichment media. These media are designed to promote the growth of Listeria but inhibit the growth of other microorganisms.