Oyster poisoning: what is norovirus?

Norovirus is a highly contagious virus responsible for symptoms of gastroenteritis (diarrhea, vomiting, etc.) that can infect oysters.

Every year, around the time of holidaysof the Oysters are infected by norovirus and thus unfit for consumption (otherwise you run the risk of it happening sick). What is norovirus? What are the symptoms of poisoning? What must we do ? What are the risks of complications? How long are we contagious?

What is norovirus?

Norovirus is a virus belonging to the Caliciviridae family. These viruses were previously known as Norwalk, Norwalk-like, or Calicivirus viruses. According to a document from ANSESthese viruses – very resistant – form the main causes of acute gastroenteritis (inflammation of the stomach and intestines) in people of all age groups. It is also thethe infectious agent most often responsible for epidemics of gastroenteritis occurring in communities (daycare centers, hospitals, schools, retirement homes, cruise ships…). The majority of foodborne norovirus outbreaks are related to the consumption of contaminated shellfish during accidental leakage of wastewater or network distribution water after network failures. Noroviruses can only reproduce if they infect a human.

What are the symptoms of norovirus poisoning?

A norovirus infection can cause symptoms acute gastroenteritis as :

  • The sudden onset of vomiting and nausea
  • Diarrhea
  • Stomach cramps
  • A moderate fever (low reported in less than 50% of cases)
  • Sometimes headaches
  • Sometimes pain
  • Sometimes chills

In healthy people the disease lasts for a relatively short time. These symptoms last on average 2-3 days (sometimes more, up to 6 days, in children and the elderly). It’s the right thing to do please consult your doctor immediately if you have these symptoms, please mention the consumption of these oysters. Immunocompromised people (elderly or people with chronic pathologies, or very young children) should be particularly alert to these symptoms, which may indicate infection with norovirus. The diagnosis is based on clinical suspicion in a patient with typical symptoms, especially during an epidemic and further PCR tests on a stool sample.

Asymptomatic people can also shed the virus.

What are the risks of complications?

In immunocompromised people or young children, norovirus poisoning can lead to complications such as:

  • a dehydration with a (significant) weight loss.
  • a electrolyte imbalance (hypokalaemia).
  • a kidney failure which could lead to death.

Is norovirus contagious?

Yes, norovirus is a virus very contagious. The peak of virus excretion in feces varies 3 to 10 days depending on the individual. Indeed, “fecal excretion may be high (up to 1011 particles/g feces) and last longer over time (two to three weeks after symptoms have disappeared). Asymptomatic people (1/3 of poisoned people are asymptomatic) can also shed the virus in significant amounts. As a result, very large quantities of virus particles are present released during winter epidemics“, reports ANSES.

What is the incubation period of norovirus?

A norovirus infection can cause symptoms of gastroenteritis, the incubation period of which can vary from 10 to 50 hours (up to about 2 days)according to ANSES.

Transfer by fecal-oral route (from stool to mouth) is the most important. A person can become infected in several ways:

By having direct contact with a sick person (caring for a sick person, sharing food, drinks or utensils with a sick person)

By touching contaminated surfaces or objects by norovirus and then putting your fingers in your mouth (contaminated surfaces, handles or taps in the washroom)

By eating food or drinking liquids contaminated with norovirus (a sick food handler who contaminates food or drinks);

Treatment: what to do in case of norovirus poisoning?

Antibiotics are not effective.

No antiviral treatment There is currently no vaccine to treat norovirus infections to prevent infection. Antibiotics are not effective. According to the PACA Regional Health Agency, the only treatment is to prescribe supportive care, such as oral rehydration (water with a little salt and sugar, oral rehydration solution found in pharmaciesjuice, clear or more consistent soup, depending on tolerance), sometimes antiemetics And oral or isotonic IV fluids (electrolyte powder to quickly rehydrate the body). Of the anti-diarrheals (loperamide for example, can be given to adults but not to children under 18 years of age who have acute diarrhea and to any patient who has recently taken antibiotics, has bloody diarrhea or has diarrhea with fever.

What prevention to prevent norovirus poisoning?

Noroviruses are resistant to conventional food storage methods (refrigeration and freezing) and to temperature (30 minutes at 60°C) and pH variations. Generally recommended precautions to prevent bacterial growth have no effect on viral contamination. Anyway, Hygiene rules must be observed in case of a sick person in the household:

► Insist on careful hand washing when leaving the toilet, before preparing and consuming meals.

► Wash fruits and vegetables carefully

► Clean contaminated surfaces thoroughly immediately after an episode of illness (vomit, diarrhea) and then disinfect with bleach

► Immediately remove clothing, sheets or other fabrics that may be contaminated after a period of illness and clean them in warm water with dishwashing liquid

► Discard any regurgitated material or diarrheal feces in the toilet and ensure the area is always clean.

► People infected with norovirus should not touch food.

► Avoid consuming shellfish if it does not come from an authorized and controlled farming area, or after prolonged cooking.

Sources: Site Reminder Conso.gouv / ANSES fact sheet: norovirus / Questions and answers on noroviruses (viral gastroenteritis) for patients and health professionals, ARS PACA

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