A virus. (NEJM Review). There are two human genogroups: genogroup I includes Norwalk virus, Desert Shield virus and Southampton virus; and genogroup II, which includes Bristol virus, Lordsdale virus, Toronto virus, Mexico virus, Hawaii virus and Snow Mountain virus. Other animals have their own genogroups,
Nausea, vomiting and diarrhea. It really opens up the sluices at both ends (PubMed).
Eating and drinking contaminated food and water; cruise ships have had outbreaks. Oysters are a good source as they concentrate the virus and the virus is not killed by either freezing or the quick cooking required for a good oyster.
"It is likely that the time and temperature of cooking required to inactivate norovirus in oysters may render the food unpalatable to consumers" (PubMed).
Vomiting spews norovirus into the air where it can infected those around the aerosolized puke or what the aerosolized puke lands on (PubMed)
Don't think bottled water is protective; in Spain it was the source of norovirus (PubMed).
Some strains cause more severe disease.
It is much harder for blood group AB to get disease.
The immunoincompetent (transplant, hematologic malignancy) can have prolonged, chronic diarrhea (PubMed).
Different strain have variable morbidity and mortality with Genogroup 2 Genotype 4 more likely to cause hospitalization and death (PubMed).
And it can be found in harbor porpoises (PubMed). So avoid porpoise sushi.
Or any sushi, as in Japan outbreaks are due to nori (dried seaweed) and the ever so hardy virus suvives the seeweed drying proceedure quite nicely (PubMed).
New strains for which there is no herd immunity pop up, or maybe poop up, from to time to cause new epidemics/pandemics. Just like influenza. Many seem to be coming out of Asia, with new strains every couple of years.
Diarrhea nausea and vomiting, fevers not uncommon. Asymptomatic shedders are not important for spread of disease (PubMed). PCR is diagnostic.
Symptoms start 12 to 48 hours after exposure and lasts for 24–72 hours.
There are multiple genotypes and unfortunately, immunity is limited to the genotype only
After an outbreak of norovirus, those affected have increased incidence of dyspepsia, constipation, and GERD (PubMed).
Very infectious, as few as a dozen viral particles can cause disease. In one study it was estimated each case infected 14 others (PubMed) .
It can survive for weeks on hard surfaces, twelve days on fabrics, and it can survive for months or years in water.
Relevant links to my Medscape blog
Last Update: 04/28/18.