What is norovirus?

Norovirus outbreaks occur throughout the year, although there is a higher incidence during the colder months in temperate countries. They infect people of all ages and cause outbreaks of acute gastroenteritis frequently, as well as sporadic cases.

Acute norovirus gastroenteritis

Acute gastroenteritis is a very common disease and its causes can be very diverse, including viruses, bacteria and parasites. Currently it is considered that one of the main causes of gastroenteritis in people of all ages are the so-called human caliciviruses, which include the norovirus and sapovirus genera. In 1972, a new virus was discovered using specific laboratory techniques in feces collected from an outbreak of gastroenteritis that occurred in a Norwalk (Ohio, USA) elementary school. For this reason, this detected virus was called Norwalk virus and is currently considered the prototype of the norovirus genus. There are strains that infect humans and others that infect animals.

It should be noted that not everyone is susceptible to a norovirus infection. Up to 20% of Europeans are considered resistant to this infection. Observational studies suggest that certain characteristics of the individual are important in the development of the disease. Children, the elderly and immunosuppressed patients are considered risk groups.

Norovirus contagion

The mode of most important transmission is the fecal-oral route. The first cases of an outbreak often appear after exposure to contaminated food or water, and subsequent person-to-person contacts spread the infection. Food can be contaminated directly from its source (eg shellfish, vegetables ...) or by food handlers who have become infected. Mollusks (oysters, clams, mussels ...) are especially dangerous because they actively concentrate the virus by filtering large volumes of water and are often eaten raw or undercooked. But nevertheless, the main foods that transmit norovirus are prepared and ready-to-eat foods, especially those that require handling, but not cooking. Noroviruses have a series of characteristics that facilitate their spread in epidemic outbreaks:

• Its infective dose is very low (it is estimated that 10 virus particles are enough to cause infection).
• The elimination of the virus by the body fluids of the affected person is very intense and persists for a long period, even after the symptoms have disappeared (up to 2 weeks).
• The stability of viruses in the environment (outside the human body) is high, and their infectivity can persist over a wide range of temperatures (from freezing to 60ºC).
• In addition, they resist acidic pH well and are relatively resistant to disinfectants such as ethanol (alcohol) and chlorine.
• It is added that the same person can suffer multiple reinfections.
• Norovirus infection spreads very rapidly in establishments such as hospitals, schools and nurseries, hotels or residences, producing epidemic outbreaks.

Norovirus: signs and symptoms

The incubation period for a norovirus infection is generally 24 to 48 hours. The disease is characterized by the sudden onset of: • nausea (79% of those affected) • Vomiting (69%) • not bloody (66%) • Fever (37%) • Abdominal pain (30%) These symptoms can persist for four to six days. Serious cases that have led to the death of elderly patients have also been described in outbreaks that occurred in nursing homes.

Treatment

There is no treatment as such, but while the gastroenteritis condition lasts, it is about carrying out a series of recommendations aimed, above all, at maintaining optimal body hydration. Currently, there are many promising challenges in developing a potential vaccine.

• Adequate hydration with abundant intake of preparations rich in salts and sugar (homemade or sold in pharmacies) and natural juices.
• Children are offered fluids frequently, preferably in small amounts at a time, to
• Avoid the intake of solids the first hours.
• Once the first symptoms have been controlled (less than 4-5 stools / day), an astringent diet can be started with foods such as toasted white bread, grilled or steamed white fish, grilled lean meat, white rice, puree carrot, roasted apple, ripe banana. Milk, fried foods, sweets and raw vegetables should be avoided.
• It is not recommended with antibiotics or antidiarrheals if it is not under medical prescription.
• If there is severe abdominal pain, you can take paracetamol.

And, above all, in the presence of high fever, very frequent diarrhea, signs of dehydration, presence of blood or mucus in the stool or in very young children, medical assistance should be sought. The insurances have a 24-hour Medical Guidance service to be able to make any questions regarding your health.

The epidemiological criteria that lead to suspicion of an outbreak of gastroenteritis are:
• More than half of those affected evolve with vomiting.
• The incubation period is 24-48h.
• The duration of the disease is 12 to 60 hours.
• Absence of detection of bacterial germs in stool culture samples.

Diagnosis

It has not been possible to isolate or cultivate norovirus human in cell culture, which makes its study difficult. One of the most important advances was in 1990 the cloning of the Norwalk virus genome. This caused the laboratory technique called ‘PCR-TR’ to become the reference technique for its diagnosis, allowing us to detect norovirus in fluid and environmental samples, in water and food, being particularly useful to discover the origin of the outbreak. In recent years, important advances have been made in the knowledge of the biological characteristics of human noroviruses. However, it would be desirable to have rapid, sensitive, specific and inexpensive diagnostic methods that would make the detection of these viruses more affordable for most laboratories. Many acute gastroenteritis with negative stool culture would then find an explanation for its cause.

Norovirus Prevention

You can act on the following levels: • Control and removal of contaminated food or water. • Maintenance of strict hygiene by food handlers and adequate disinfection of surfaces. • Reduction of secondary cases by minimizing contact between people. • Measures to avoid contamination of mollusks at source by prohibiting the discharge of sewage from boats.