September 26th 2016

Norovirus is one of the most contagious causes of gastrointestinal illness known to man. Among the very young, the very old, and the immunocompromised, norovirus infection can be severe and life-endangering. Because more than 80% of norovirus infections occur between November and April, it’s time for clinicians to prepare.

Norovirus is one of the most contagious causes of gastrointestinal illness known to man. Among the very young, the very old, and the immunocompromised, norovirus infection can be severe and life-endangering. Because more than 80% of norovirus infections occur between November and April, it’s time for clinicians to prepare.

Between 19 and 21 million Americans are infected with norovirus annually. Approximately 10% of them are so ill that they seek acute care. In years when a new strain emerges, statisticians record about 50% more cases. Large pandemics in 2002-2003 and 2006-2007 were particularly virulent, but a new pandemic strain emerges every 3 to 4 years.

About half of norovirus outbreaks are related to contaminated food. Usually, the source is leafy greens, fresh fruit, or shellfish. The virus can appear in the stool before the patients develops symptoms and remain in the stool for about 2 weeks.

Once an individual is infected, his or her contacts are at high risk for infection. They can pick it up by touching surfaces or objects contaminated with norovirus and then touching mucous membranes, or simply having contact with someone who is infected with norovirus.

Why It Spreads

Patients who experience this infection’s gut-wrenching nausea, diarrhea, and vomiting are often angry at the individual(s) they perceive “gave it to them.” It’s difficult to explain to patients just how contagious this virus is, spreading at lightning speed. Its viral particle has a diameter of about 38 nanometers (3 norovirus particles can fit across the width of a single strand of hair).

A good way to explain its ability to travel is this: the molecule that creates the smell from freshly baked cookies is less than a nanometer in diameter, so small that gravity has minimal effect on it. That’s why you can smell cookies baking all through the house. Similarly, tiny, norovirus particles travel quickly and easily and land on all kinds of surfaces. Although its main route of transmission is fecal-oral, airborne transmission is possible.

Furthermore, norovirus lacks a lipid envelope—a trait that makes it resistant to hygienic control with alcohols and detergents—and has a single-stranded, positive sense RNA genome. Norovirus survives temperatures from freezing to 60°C (140°F). Only high heat and chlorine-based disinfectants inactivate norovirus quickly. Unfortunately, studies have determined that infected individuals infect more than a dozen others before those around them realize that sanitary precautions are needed.

Symptoms and Treatment

Concurrent diarrhea and vomiting are common. Most infected patients will experience a virulent bout of norovirus illness and recover within a few days, but approximately 10% experience more serious symptoms. Acute dehydration is a serious concern.

Supportive therapy is the sole available intervention at this time to treat norovirus infection. If the patient is able to drink, advise him or her to consume oral rehydration with fluids and electrolyte-containing beverages. Severe vomiting and diarrhea warrants a trip to the emergency room, where intravenous fluids must be started. If fever or other red flags develop, the patient may need hospitalization.

A final word about eating: For years, we’ve advised patients who have diarrhea not to eat for 24 hours at least. However, current studies reveal that early feeding decreases intestinal permeability caused by infections, reduces illness duration, and improves nutritional outcomes. So, if patients are hungry and can keep food down, they can and should eat.

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