Norovirus is a highly contagious virus that causes flu-like symptoms of nausea, vomiting, diarrhea and abdominal cramping.

(Image from CDC website)

The dreaded “stomach flu” that hits particularly hard in winter is not a flu at all. It is norovirus, a highly contagious virus that causes symptoms of diarrhea, vomiting and stomach cramping. According to the Centers for Disease Control and Prevention (CDC), the illness often begins suddenly and lasts for one to two days with no long-term adverse health effects. True “flu” is a respiratory disease caused by the influenza viruses; sometimes the “true flu” can also cause gastrointestinal symptoms similar to norovirus. Getting an annual flu vaccine can help prevent flu; unfortunately, there is no vaccine for the norovirus and antibiotics, useful only for bacterial infections, do not help.

Norovirus is extremely common and has gained notoriety as a vacation cruise spoiler and an unwelcome visitor in child and adult care facilities, schools, restaurants, hospitals and dormitories. Norovirus particles are extremely small and are discharged by the billions in the stool or vomit of infected people, according to CDC. Yet, fewer than 100 virus particles are highly likely to make a person sick. The virus spreads through direct contact with an infected person or when an individual touches a contaminated surface and then touches their mouth or even their nose.

A 2011 study found norovirus is the leading cause of foodborne illness in the US, responsible for 5.5 million cases each year. In many cases, sick food handlers are responsible for these outbreaks. Eating foods contaminated with norovirus is a leading cause of hospitalizations.

Recipe for an Outbreak

Close quarters and a breakdown in sanitation is the simple recipe for a norovirus outbreak. Attention to surface disinfection is critical to controlling the spread of norovirus. Proper hand washing is another “must” as the virus can be transmitted easily via contaminated hands. It is important to know that a norovirus carrier can infect others for at least three days after recovery.

These steps, from CDC, can help reduce your risk of contracting norovirus:

• Wash your hands carefully with soap and water, especially after using the toilet and changing diapers and always before eating or preparing food.
• Carefully wash fruits and vegetables, and cook oysters and other shellfish thoroughly before eating them.
• If infected with norovirus, do not prepare food for others while experiencing symptoms and for three days after recovery (see Norovirus: Food Handlers).
• After throwing up or having diarrhea, immediately clean and disinfect contaminated surfaces by using a solution made with chlorine bleach and water:

Disinfecting against Norovirus with Chlorine Bleach

• Immediately remove and wash clothing or linens that may be contaminated with vomit or stool. Handle soiled items carefully—without agitating them—to avoid spreading the virus. If available, wear rubber or disposable gloves while handling soiled clothing or linens and wash hands after handling. Soiled items should be washed with detergent at the maximum available cycle length and then machine dried.

Joan Rose, PhD, is the Homer Nowlin Chair in Water Research at Michigan State University and a member of the Water Quality and Health Council.

¹http://emergency.cdc.gov/disasters/disease/pdf/diarrhea-evac.pdf
²http://health.utah.gov/epi/diseases/norovirus/Guidelines_for_Environmental_Cleaning_125846_7.pdf

Scientists confirmed this theory recently in a report published in The Journal of the American Medical Association, which found that one-third of California patients hospitalized with H1N1 flu were given a rapid test that came back negative. A different test that uses more sophisticated technology confirmed they had H1N1.

The discrepancy is caused by the high specificity (80-90 percent) and the low sensitivity (10-70 percent) of the rapid test for influenza A. The test often does not identify influenza A, especially in adults, who don’t shed as much virus as children. Therefore, correctly identifying those with influenza A, which could be either H1N1 or seasonal flu, is the real issue with the rapid tests. Since about 90 percent of circulating influenza A is H1N1, doctors can be fairly sure that anyone with flu-like symptoms who is also positive for influenza A – either on the rapid or more advanced tests – has H1N1 flu. But, there is still a 10 percent chance that it is seasonal flu.

Regardless, many are not taking the chance that their illness could be something other H1N1. Dartmouth pediatrician Hank Bernstein, who’s on the American Academy of Pediatrics’ infectious diseases committee, said in a recent USA Today article, if symptoms look like the flu, “it’s H1N1 until proven otherwise, almost.”

Stephen Baum, an infectious-disease physician at New York’s Albert Einstein College of Medicine, in the same USA Today story, says: “If you test positive, you got it. If it’s negative, you may still got it.”

Therefore, it is important to understand the symptoms of flu versus a common cold. Those symptoms, not the test results, should be the trigger to take relevant action – either treatment or protecting others from exposure. Further, a negative test shouldn’t make one complacent in taking steps to prevent spreading the flu. Learn what you can do to keep your family healthy this winter by visiting the “Prevention and Treatment” section on the Centers for Disease Control and Prevention H1N1 website.

(Jerod M. Loeb, PhD, is Executive Vice President, Division of Quality Measurement and Research, The Joint Commission, and a member of the Water Quality & Health Council).