Cases of norovirus have been surging around the United States in recent weeks. Norovirus is a very contagious pathogen that is the primary cause of diarrhea and vomiting in the US, according to the US Centers for Disease Control and Prevention (CDC). More than 2.2 million outpatient medical visits and 465,000 emergency department visits are due to this virus every year.
Norovirus infections can also cause stomach pain, dehydration, headache, fever, and dizziness. Anyone can be infected with the virus. There are an average of 2,500 norovirus outbreaks every year in the US alone, but over half of US norovirus outbreaks happen in long-term care facilities.
Although people can develop immunity against norovirus after being sickened by it, there are many subtypes of norovirus, so a person can get sick from different versions of it many times throughout their life. We also don't know how long immunity against norovirus may last.
There are no specific treatments for norovirus, and illnesses usually resolve on their own after one to three days. Since antibiotics only treat bacterial infections, they are not useful against norovirus.
People who have recovered from norovirus infections can remain contagious for a few days after recovery, however. So the CDC advises anyone with symptoms to stay at home for two days after symptoms have ended. Severe norovirus infections can also arise in people under the age of five, or individuals who have weakened immune systems.
Since individual cases of norovirus do not have to be reported to local health authorities, it can be very difficult to know exactly how many people are getting sick from the virus, since so many cases probably go unrecognized or undiagnosed. Clinics and hospitals also do not usually test for the virus.
There are some monitoring systems, however, which try to estimate how many people might be sick from norovirus at any given time, while another looks for changes in the norovirus genome.
Norovirus infections can be prevented with good handwashing practices, and it is advised to thoroughly wash fruits and vegetables before consumption. Some norovirus outbreaks have been due to contaminated leafy greens and fresh fruits. Laundry should also be washed in hot water, and contaminated surfaced should be disinfected. Raw and undercooked shellfish can also carry the virus, so anyone who wants to avoid the illness should not eat those foods, like raw oysters.
Sources: CDC, The Associated Press
