Part 1 norovirus and shellfish

Speaking of things that cause the norovirus, what you think of what kind of ingredients?
I think many people the image of the "oyster" first and foremost.
Sometimes, I hear on the news coverage of food poisoning, and ｒaw oysters many cases that were infected with the virus in the cause for sure.
However, rather than confined to oysters, in the case of bivalve, or eaten raw, or when heating is not enough, there is a possibility that it is caused by infection with noroviruses.

Such as clams and oysters from, whether they are infected with the norovirus us, why, have you ever thought about you?
So, in the first place, why do you have a norovirus such as oysters?
In fact, that we, human beings are making the cause of the first place that I like.
The first route cause or whatever, a person infected with norovirus, symptoms of vomiting and diarrhea will be reported, it is supplied to the toilet is flushed into the sewage treatment plant in the end.
And, in the sewage treatment plant, so you can not remove all the viruses contained in the vomit or diarrhea, a slight virus we will flow into the sea or river.
Then, clams and oysters are eating plankton as food, in that case, I would breath in a large amount of water as well.
Virus remains, day by day, it is concentrated, and internal organs of oysters, accumulate.
Or eating raw shellfish that has been contaminated with norovirus, heating or if not enough, man is thus being contaminated.