Gastroenteritis: these 5 surprising facts to know to escape it

It's a great winter classic: in recent weeks, gastroenteritis has made a comeback in France, as in all European countries. Between Christmas and the New Year, the rate of consultations in general medicine for acute diarrhea jumped by 39%, according to Public Health France. The viruses responsible for this intestinal infection are of course prevalent all year round, but even more so in winter, when the cold increases our promiscuity. “It had calmed down considerably in recent years with the confinements, and it has been increasing since 2022. This year could be a big year for gastroenteritis,” predicts Professor Alexis de Rougemont, director of the National Reference Center for gastroenteritis viruses. -enteritis at Dijon University Hospital. Duration of contagiousness and immunity, mode of contamination... Whether or not you have already been affected, it is time to read this article to avoid a bad time.

If someone tells you they have just recovered from “gastro”, be wary... because they may still be contagious! Indeed, the incubation period (time between contagion and the appearance of symptoms) is very short (24 hours on average), as is that of the disease (2 to 3 days), but the period of contagiousness is fearsomely long. And contrary to what one might believe, it is not at all correlated with the presence of symptoms. The peak of excretion of the virus in the stools occurs 3 to 10 days after infection, but the patient continues to shed it two to three weeks after the symptoms disappear! In babies and the elderly, this period can be extended to 6 weeks. As for immunocompromised people, they can emit norovirus (the main cause of gastroenteritis) in their stools beyond the age of 2.

Even if the illness is for you more than an ugly memory left in your rearview mirror, it is better to continue to wash your hands meticulously (especially before cooking or taking public transport) and to clean potentially contaminated, such as toilets. The ideal is not to share the little corner with others during this risky period.

The viruses responsible for gastroenteritis (norovirus and rotavirus) are very contagious. They are transmitted very easily and quickly, mainly by the fecal-oral route. The mechanism is simple: a sick person vomits or has diarrhea. One way or another, she ends up with many copies of the virus on her hands. If she ignores their methodical washing, she will sow the virus everywhere behind her: on door handles, in public transport, on her kitchen utensils... But not only does a patient emit large quantities of virus (several million particles per milliliter of stool or vomited matter), but noroviruses are also extremely resistant in the environment. They then just have to wait patiently for another human – by touching an infected surface, then bringing their hands to their mouth – to offer them a new base. You can also be contaminated by direct contact with the patient (note that the virus can also be found in saliva). And to be contaminated, you don't need a large quantity of virus: “less than 100 particles are theoretically enough to cause the disease,” emphasizes Professor Alexis de Rougemont.

You recently saw this friend who told you that his partner had just come out of a bad “gastro” episode. There too, distrust. Because he could also be infected, even if he doesn't look like it! “Among people in contact with the virus, a significant proportion will not develop symptoms, but they can still shed the virus in significant quantities,” warns Professor Alexis de Rougemont. We then speak of “asymptomatic” cases, as is the case for Covid-19. It seems like nothing, these lucky people are actively participating in the growth of the epidemic. So if one or more people in your household get sick and you don’t, consider yourself lucky and still wash your hands well!

This is good news: only about half the population is susceptible to norovirus, the main cause of gastroenteritis. This is partly explained by the fact that some people develop very effective immunity at the intestinal level, from the start of the infection. For others (around 20% of the population), this protection is due to a genetic particularity which gives them natural resistance to norovirus. “We normally have an enzyme which synthesizes ligands on the surface of intestinal cells,” explains Professor de Rougemont, “These ligands are essential for the virus to be able to replicate. However, some people have a mutation in this enzyme, they do not produce a ligand and are therefore naturally protected.”

If you belong to the other category, not only is immunity following infection short (a few months to a year), but it is also very partial. Noroviruses in fact represent a large family of viruses, and the immunity acquired following infection by one of its members does not work on the others. It is therefore entirely possible to have two “gastros” very close together, due to two different viruses.

Also read: Food safety: health controls in question

You may have experienced the scene during the holiday season: one of your loved ones got sick after eating an oyster. A few days later, other family members developed the same symptoms. But this time, the oysters could not be incriminated since a period of a few days had passed since their consumption, or perhaps they themselves had not eaten any... How to explain that they were still affected?

If humans are the main reservoir of noroviruses, oysters can be considered secondary and temporary reservoirs. “We have demonstrated the existence of specific ligands in oysters which allow noroviruses to attach to them,” explains Soizick Le Guyader, head of the Health, Environment and Microbiology laboratory at Ifremer, specialist in noroviruses. But there is nothing to detect the presence of the virus with the naked eye. “Contaminated oysters are not diseased, the virus is not capable of multiplying there. This does not change their appearance or smell at all,” the scientist further specifies. However, the virus is indeed present there, and capable of making you sick. However, oysters should not be too blamed: their contamination by viruses causing “gastro” is always secondary to the release of contaminated fecal matter into the environment by populations, while an epidemic of gastroenteritis is rife. This is why every winter, shellfish production areas find themselves closed to sale.