What is the norovirus natural habitat or host? how does it start up an outbreak? where does it go when outbreaks die down?

Norovirus: Norovirus is the most common cause of viral gastroenteritis. Person to person transmission is the most common route, although it can also be transmitted from bad food or water. it is often passed by being in the same room as someone who vomits. Since it is passed fromperson to person, an outbreak never "dies down" completely. Contaminated shellfish and salad are the most common infected foods.

CDC: The studies I read on the CDC's website suggested the most common mode of transmission is foodbourne, with restaurants, schools, hospitals, and long-term care facilities being at the top of the list of most common places to contract it. It most likely always is alive in some food or someone but transmission is held at bay or can be increased depending on contact and hand washing.