The actual data (and risks) behind listeriosis. Is it as serious as it seems?

The listeriosis outbreak caused by the consumption of meat mecha of the brand La Mechá adds patients by tens and alarm throughout Spain. The bacteria that causes the disease, Listeria monocytogenes, is dangerous and worries in the food industry, because the figures show that in recent years the cases do not stop increasing.

A recent study published by the Carlos III Health Institute and the Ramón y Cajal University Hospital in Madrid draws the real incidence of the disease in Spain. Between 1997 and 2015, 5,696 hospitalizations were recorded. In principle, they do not seem many, considering that this figure includes a total of 19 years and that in this period the Spanish population exceeded 46 million, but the authors clarify that the number of affected is much higher, because the vast majority of the cases are mild and do not require admission.

However, the most significant data is that of the evolution of the number of hospitalized patients: while in 1997 the ratio was 0.67 per 100,000 inhabitants; in 2013 it was 1.01. The increase is slow but steady over the years.

People over 65 years accumulate 50% of hospitalizations by listeriosis. In addition, this age group is also the one that has suffered a most marked increase in the number of cases in the last two decades. Other risk groups are immunosuppressed people for various reasons (such as cancer, diabetes or liver disease). In addition, pregnant women account for 7% of hospitalizations and newborns, 4%.

The severity of listeriosis is best understood with other data: 17% of these hospitalizations ended in death. Again, those over 65 get the worst, with 67.5% of deaths. We also found important geographical variations: northern Spain is most affected. Catalonia is the community with the highest number of hospitalizations, followed by Cantabria, La Rioja, the Basque Country and Galicia. On the contrary, Murcia, the Valencian Community and the Canary Islands are the ones that register fewer cases.

Data from the European Food Safety Authority (EFSA) indicate that there is “across the continenta growing and statistically significant trend of confirmed cases of listeriosis ”, at least during the period 2008-2017, according to Teknautas, a spokesman for this entity, who is responsible for the scientific analysis of food risks.

The latest annual report on zoonotic infections and outbreaks of food-related diseases, prepared by EFSA and the European Center for Disease Prevention and Control (ECDC) and published at the end of last year, indicates that in 2017 2,480 cases were registered in the European Union. Recently, other countries have gone through a similar situation to which Spain lives these days, with an outbreak of listeriosis from consumption of salmon and smoked trout that affected five countries last June (Denmark, Estonia, Sweden, Finland and France) and caused several deaths.

The causes of the increase recorded in recent years are not clear. “It may be due to a increase in prepared food products, ready to consume, more susceptible to contamination ”, explains Miguel Ángel Lurueña, specialist in food technology, consultant and disseminator. "But it is also true that we are diagnosing better and better and that is now when we started to have good statistics, because in Spain listeriosis has not been mandatory until 2015," he adds.

EFSA says that this disease "is still relatively rare compared to other foodborne infections," but admits that It is one of the most serious for its consequences, especially for vulnerable people.

Why is it so dangerous

The truth is the mortality rate of listeriosis is extremely high when comparisons are made According to Lurueña, another foodborne bacteria, called Campylobacter (usually related to gastroenteritis and diarrheal diseases), only causes death in 0.22% of cases diagnosed in Europe.

However, Listeria monocytogenes is a very peculiar bacterium. “He only dies with heat. It is able to resist the salt of sausages, the acidity of lemon and vinegar and the low temperatures ”, he emphasizes. While other microorganisms are unable to reproduce in the refrigerator, the listeriosis bacteria continues to multiply. Therefore, in theory, it could appear in foods that have not been subjected to thermal processes, "Like sausages or salads that are already packaged in the supermarket, ready to eat."

However, we must start from the basis that All foods sold are safe.. "Of course accidents can occur, as in this case, but I think that an exaggerated alarm is being generated, we are talking about an outbreak that starts from a single company," says Lurueña, as confirmed by the Ministry of Health, Consumer Affairs and Social welfare

"The problem is that generates distrust in the food industry in general and in the end people are afraid, "he acknowledges," but so far there has never been such a large outbreak in Spain. " Although the number of deaths from listeriosis is around 70 a year in our country, almost all are due to isolated cases that are not related to each other, as has happened just these days with the death of a man in Cantabria, a case that does not It is linked to the products of the Sevillian company that sells the La Mechá brand.

What can fail to happen

Taking into account all the controls that pass the products that are put on the market, it is worth asking where the fault is. “In this case, the roasted meat is cooked, so a possible explanation could be an error in the oven temperature control, so that the center of the product did not reach the 65 degrees Celsius required to destroy the bacteria, ”he puts as an example. However, this explanation does not seem to make much sense, since the meat was well made. "Most likely, contamination has occurred between cooking and packaging, but it should be checked," says Lurueña.

This hypothesis would imply that Some part of the facility suffers a cleaning problem Technically known as 'biofilm': it occurs when microorganisms accumulate and create a film that protects them. Although a surface is apparently clean, it may contain this bacterial film, very difficult to eradicate. In fact, the food industry invests many resources in disinfecting and, sometimes, even has to end up replacing machinery. "The bacteria can persist in food processing environments for prolonged periods, contaminating a wide range of foods, especially during the processing stage," confirms the EFSA spokesperson.

Although the industry is responsible for food safety, consumers also have to do their part: "The fact that a prepared salad is safe does not mean that we can take it to the beach and leave it five hours in the sun before consuming it, we are also responsible for what we do as consumers," says Lurueña.


The first tip is to wash the foods that are going to be consumed raw, such as fruits and vegetables, in addition to the utensils we use to prepare them and our own hands. The second is to separate food, for example, "we should not cut raw chicken and tomatoes on the same table ". The third recommendation is to refrigerate: although the bacteria can reproduce cold, low temperatures will always make it more difficult. And finally, in those foods that we cook, heat enough until they are well done.

To this it should be added that risk groups should exercise some of these precautions, for example, disinfecting vegetables with water and bleach that are going to be consumed raw or peeling the fruit. In the case of pregnant women, it would be advisable to dispense with raw foods, such as sushi or sausages.