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Norovirus outbreak linked to oysters in Canada last month has put health authorities on high alert. According to Science Alert, health officials said that more than 200 people have been sickened by the virus.

California Department of Public Health (CDPH) May 1 has warned people to avoid eating raw oysters from British Columbia after around 100 people fell sick in the state.

Norovirus is highly contagious and one can contract the virus by coming into close contact with infected patients or by consuming food and water carrying the virus. Oysters and shellfish are often responsible for spreading the disease.

Oysters are often linked to norovirus outbreak, which has led to scientists to conclude that these oysters are probably living in polluted water.

According to reports, shellfish often carry the virus when they are exposed to untreated human sewage. Oceans are often polluted by septic systems, when untreated wastewater is drained in oceans, and even when callous beachgoers excrete in the sea.

Shellfish find food by filtering water through their bodies. This process makes the norovirus particles accumulate inside the organism, said Washington State Department of Health.

Experts have advised people to make sure that the food they are eating is washed properly. In case if they are eating some shellfish, they should cook it thoroughly until the food reaches an internal temperature of at least 63 degrees Celsius (145 degrees Fahrenheit).

Symptoms of norovirus infection can range from diarrhea, vomiting, and nausea to fever and body ache, according to Centres for Disease Control and Prevention (CDC). Also, according to its estimation, each year 19 to 21 million people are contaminated, which leads to 570 to 800 deaths.