Is the Norovirus the Same as the Flu?

What Is Norovirus?
What Is Norovirus?.

Whenever I have a patient come in with a stomach virus, they usually think it is from the flu virus and wonder why their flu shot did not prevent their illness. The Norovirus, another gastrointestinal virus, is often confused with the flu, but is a completely different group of viruses.

Norovirus is a name given to describe a group of related viruses which are the most common cause of viral gastroenteritis (infection of the stomach or the intestines) in the United States.

Most who are infected suffer a short course of illness, however, others can become infected and remain asymptomatic.

By the Numbers

While the misery that can be associated with Norovirus infections is typically short-lived, the overall disease burden is staggering. The below statistics represent the cumulative impact caused by Norovirus annually in the United States.

  • 21 million illnesses
  • 800 deaths
  • 71,000 hospitalizations
  • 400,000 emergency room visits
  • 1.9 million outpatient visits

To put these statistics into perspective, it is estimated that an average American living to 79 years old can expect to experience approximately 5 episodes of gastroenteritis caused by Norovirus during his or her lifetime! In fact, it is estimated that 90% of young adults have already developed antibodies to Norovirus.  In spite of this, immunity does not last since Norovirus is a group of multiple viruses rather than a single virus so repeated infections are common.

Symptoms and Course of Illness

Norovirus is the most frequent cause of gastroenteritis in the United States. The onset of symptoms is usually abrupt and occurs within 12 to 24 hours of exposure. The chief complaints associated with infection are vomiting and non-bloody diarrhea. Other symptoms can include nausea, fever, fatigue, headache and body aches, or generally feeling “blah.” While most people develop both vomiting and diarrhea, some do present with one of these symptoms alone.

Those who do experience diarrhea may report up to 8 to 12 stools per day.

Diagnosis is usually made based on the presenting symptoms with treatment aimed at symptom management. While not routinely used in the management of single episodes affecting only one individual, in the case of suspected mass outbreaks, stool samples can confirm the presence of Norovirus as opposed to other similar viruses or infections caused by a bacterial origin. In fact, the presence of the virus can be found in the stool even before symptoms occur and can be shed in the stool for as long as weeks following recovery.

Most cases of Norovirus are self-limiting and tend to resolve just as quickly as they began, usually within 48 to 72 hours. Since the infection is viral in nature, antibiotics will not speed up recovery. However, symptom management can help. This includes prevention of dehydration since vomiting and diarrhea can quickly lead to fluid loss. Those most susceptible to complications include young children, persons of advanced age, and those who have underlying chronic conditions or weakened immune systems.

In Case You’re Wondering…

Are you wondering just how Norovirus causes vomiting and diarrhea? If so, here is the scoop.

Norovirus wreaks havoc on the digestive system in a couple of ways. First, it can delay gastric emptying of food and liquid from the stomach, which explains why more than half of those infected report illness associated with vomiting episodes. Second, it can cause changes in the jejunum (the middle of three segments of the small intestine) which impairs absorption of food and decreases enzyme production. Together, these can result in a change in intestinal secretions which can lead to frequent watery stools.

Managing Norovirus

Norovirus is highly contagious, and can spread through an oral-fecal route, and even through the air via vomit.

  This is the reason you hear about it on the news when a large outbreak happens, like on a cruise ship.  A food server may not even know they have been affected and when they prepare food, an outbreak can take place. 

Scientists are currently researching vaccines and conducting clinical trials in hopes of one day offering immunity from Norovirus. Until then, awareness of a possible infection and strict handwashing is the only way to control the virus.

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