One of the recurring news stories every summer is the spike in foodborne foodborne illnesses, usually associated with the season's high temperatures. But unlike the salmonellosis headlines of other years, the summer of 2019 will go down in history as having seen the largest outbreak of listeriosis on record in Spainwith a issue of cases that possibly has not yet reached its peak, taking into account that the incubation period of the disease can last up to 70 days.

Listeriosis is a foodborne disease caused by the ingestion of food contaminated with the bacterium Listeria monocytogenes. In the healthy population the disease presents as a mild gastroenteritis, with symptoms such as diarrhea, fever and muscle pain. However, the invasive form manifests itself mainly in the immunocompromised population (elderly, children, transplant recipients, chronically ill and pregnant women), and can lead to severe syndromes such as encephalitis, meningitis, endocarditis, septicemia and miscarriages. For this reason, although the incidence of listeriosis is much lower than campylobacteriosis and salmonellosis (the main foodborne diseases in Europe), the mortality rate is 13% according to the latest report of the European Food Safety Authority (EFSA), compared to 0.04% and 0.25% in cases of campylobacteriosis and salmonellosis, respectively.

While Salmonella bacteria do not need presentation, Listeria monocytogenes is a pathogen unknown to most of the population. It is a very ubiquitous microorganism and has been isolated from soil, water, vegetables and intestine of humans and animals, among other environments. This great dissemination makes its presence frequent in fresh foods (meat, fish, milk, fruits and vegetables), although fortunately for us, this bacterium is easily destroyed with heat (65ºC-70ºC) and with chlorinated disinfectants for food use. The problem is found in processed and ready-to-eat foods, which may have been contaminated with the microorganism during processing, distribution and storage and which are consumed directly without any additional culinary treatment subject . Thus, food groups that have been implicated in outbreaks of listeriosis include cheeses, smoked salmon, pates, cold cuts, sandwiches, as well as the larded meat in the recent episode. These foods are usually kept refrigerated because the cold acts as a barrier to prevent or slow the growth of pathogens. However, this is not the case with Listeria monocytogenes. This bacterium has the characteristic of being able to multiply at refrigeration temperatures (which gives it the nickname of psychrotrophic bacteria), although the more leave is the temperature of the refrigerator, the slower its growth rate will also be. That is, it is more difficult for it to multiply at 4ºC than at 8ºC and of course it will multiply faster at ambient temperatures (if the cold chain is broken, the pathogen will reach risk concentrations in a few hours). For this reason, most manufacturers of ready-to-eat foods indicate on label "keep between 0 and 4ºC".

When food alerts such as the one we are experiencing occur, we always wonder if the food we consume is really safe. The truth is that there has never been more food safety as we have in our days, with surveillance, controls and inspections at different levels. The food industry is ultimately the manager to ensure the safety of the products it produces and according to Regulation (EC) 852/2004 must have implemented self-monitoring systems to detect hazards, control them and minimize risks. Regulation (EC) 2073/2005 on microbiological criteria for foodstuffs further specifies that "food business operators producing ready-to-eat foods likely to pose a risk to public health from Listeria monocytogenes must always take samples from production areas and equipment, as part of their sampling plan, in order to detect the possible presence of the bacterium". Public administrations ensure compliance with the legislation and carry out regular inspections.

However, 0 risk does not exist because it is not possible to analyze 100% of the food we consume. Therefore, consumers must also be aware of their active role in food safety. On the one hand, by respecting basic hygiene rules during food processing and preservation, such as thorough cooking, cleaning and disinfection of surfaces and utensils, storage of raw materials and processed foods at safe temperatures and prevention of cross-contamination. This implies avoiding the contact between raw and cooked food and paying special attention to the use of cloths and cloths that can be a source of dispersion of microorganisms in our kitchen. And on the other hand, to know which subject food could be more dangerous due to the potential presence of pathogens and/or our condition of population at risk. Thus, the immunocompromised population should be aware of the risk they assume when eating ready-to-eat foods that do not require any treatment that destroys an eventual presence of Listeria monocytogenes. And the general population should know which is the coldest shelf in their refrigerator to safely store these food groups until the time of consumption.

Although this outbreak of listeriosis can be considered exceptional because of the issue number of people affected, the truth is that the latest EFSA reports show an upward trend in the issue number of cases of listeriosis reported each year, probably associated with the increase in the population at risk and new consumption habits. Food safety is guaranteed from different areas and it is in the hands of the food industry, public administrations and the consumers themselves to reduce the incidence of food poisoning. core topic