Norovirus Symptoms and Testing

 As the name suggests, norovirus is a virus.  It causes an infection in the digestive tract.  This infection will often irritate the stomach and intestines, gastroenteritis, and is often incorrectly thought to be a stomach bug or the stomach flu. There are many common symptoms of the norovirus, including diarrhea, nausea, sudden stomach pain, and vomiting. 

The norovirus is extremely contagious and will spread through ingesting contaminated liquids or foods, touching contaminated surfaces, and coming into close contact with infected people.  Those who are contagious may spread the virus for much longer than they are actually ill with it.  This is due to norovirus being present in the stool before signs and symptoms are exhibited, and for up to two weeks after the person starts to feel better. 

The CDC (or the Centers for Disease Control) believes that norovirus affects approximately 20 million people in the US each year.  This makes it the most common cause of food poisoning in the country.  It is also considered the most common cause of acute diarrhea in healthy adults. 

As norovirus can rapidly spread, outbreaks in college dorms, daycare centers, schools, nursing homes, cruise ships, and other places where food is served, and people stay in close contact can occur.  People who live in these settings are at a higher risk of catching this virus.  

Drinking and eating in a place where food handling procedures are unsanitary is another common cause of infections.   

Anyone can become infected, but most people will recover in a few days.  However, the elderly, young children, and people who have underlying health conditions and weakened immune systems, can have further problems.  The infection can cause serious complications such as severe dehydration that can be fatal if not treated.  After being infected, people do not become immune and can be re-infected multiple times throughout their lives.   

The Symptoms 

People who have been infected by the norovirus will start to show signs within 12 to 48 hours following exposure.  The symptoms of this virus will last for one to three days on average.  Some of the common symptoms and signs include: 

  • Nausea 
  • Diarrhea 
  • Fever 
  • Body aches 
  • Stomach pain 
  • Vomiting 
  • Headache 

As the norovirus causes diarrhea and vomiting several times a day, it can easily lead to dehydration.  The signs of dehydration include less frequent urination, dizziness, and dry mouth.  Dehydration can be dangerous to the elderly, young children, and people who have underlying medical conditions. 

Laboratory Testing 

Usually, norovirus is diagnosed clinically, by considering the person’s signs and symptoms, the severity and duration of the symptoms, and what the person has recently eaten. 

Laboratory testing is not usually performed except if the person has a higher risk for complication from infections or if the symptoms may be part of a broader outbreak, may be caused by a different condition with the same type of symptoms, are severe and/or last more than a few days. 

If public health authorities suspect an outbreak, testing may be conducted to figure out whether it is norovirus or another microbe causing the illness.   Also, testing may be implemented to manage/contain outbreaks or to track cases and their locations. 

Infected people who are at a higher risk for complications and those with severe illness should have a stool sample analyzed in a laboratory.  There is a range of tests that can be used to diagnose norovirus and rule out any other type of infection. 

Gastrointestinal pathogens panels will look for multiple gastrointestinal microbes that cause disease and show in stool samples.  

Individual molecular tests, including PT-PCR, will look specifically for norovirus in the stool sample.  These are the preferred tests for diagnosing any norovirus infection. 

Stool culture tests will look for several bacterial pathogens that are common, including Shigella and Salmonella.  These infections can cause symptoms that are similar to the norovirus.   

Stool WBC (or white blood cells), as the name suggests, looks at the number of white blood cells in the stool, which can be an indicator of infection from parasites and bacteria.  People who are infected with norovirus will generally not have these cells in their stool. 

O&P (or ova and parasite exam) is done to rule out any potential parasite infections because the symptoms of these infections are similar to the norovirus.  This is a good test for anyone who had traveled internationally before their symptoms appeared. 

FOBT (or fecal occult blood test) is ordered in cases where bloody diarrhea occurs and identifies the illness causing the bloody stool.  Occult blood will not be present in a stool that has norovirus.   

There are other general tests that will also be performed should someone become very ill.  This includes when a person suffers from dehydration and a high fever.   

Blood cultures are sometimes ordered to rule out any bacterial infections which spread into the blood. 

BMP (or basic metabolic panel) is a test panel used to monitor potassium and sodium as well as acid-based imbalances in people who suffer from severe dehydration to ensure proper organ function. 

CBC (or complete blood count) is a panel that is sometimes ordered to determine if there is an increase in white blood cells pointing to bacterial infections. 

Preventing Norovirus 

To protect against getting this highly contagious virus and the accompanying infection, a person should: 

  • Thoroughly wash hands often, especially after handling diapers or using the restroom and prior to handling or eating food. 
  • Stay away from contaminated food and water, and food prepared by someone who has, or has recently had, norovirus. 
  • Cook seafood thoroughly and wash vegetables and fruits. 

People who have had recent norovirus infection should: 

  • Use a chlorine bleach solution to disinfect virus-contaminated surfaces. 
  • Stay at home – don’t go to work and avoid other activities, especially food handling. 
  • Keep sick children at home. 
  • Avoid traveling until signs and symptoms have passed and keep washing hands. 

Treating Norovirus 

Like many food and waterborne illnesses, norovirus does not usually require treatment beyond supportive care like drinking fluids and resting.  The symptoms will often go away within a few days in otherwise healthy people. 

Antibiotics are not effective because norovirus is not a type of bacteria. People older than 65 may be prescribed anti-diarrheal medication.  Intravenous fluids may be required in cases of severe symptoms and significant dehydration, along with hospitalization.