Norovirus

This information has been prepared by Adair Hoover, Program Assistant, Food Safety and Preservation, Clemson University and Dr. Susan Barefoot, Professor Emerita & Leader, Food Safety & Nutrition, Clemson University, 08/13.

HGIC 3743

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Introduction

Norovirus is a virus that causes gastrointestinal illness. It is highly contagious and one of the most common foodborne pathogens. Norovirus is responsible for more than 50% of foodborne outbreaks, causes at least 5.4 million illnesses, 14,600 hospitalizations and 149 deaths annually. The virus is often referred to as the “stomach flu” but is not related to influenza which is a respiratory illness caused by the influenza virus. You can become sick with a norovirus illness many times in your life.

Symptoms of Illness

The primary symptoms of norovirus infection are nausea, vomiting, diarrhea and abdominal cramps. Some people may have additional symptoms including, headaches, fever, chills and muscle pain. The norovirus illness is usually brief in healthy individuals (1 to 3 days) but can be serious for children and older adults. Symptoms of norovirus illness usually develop within hours or a few days after you are infected and last a couple of days. People infected with the norovirus are contagious from the moment they begin feeling ill and will remain contagious for a minimum of 3 days and up to two weeks. 

Dehydration & the Norovirus

Most people who get the norovirus recover completely without any long-term problems. However, people who are unable to drink enough fluids during the course of the illness may become dehydrated. Dehydration can lead to serious problems and severe dehydration can sometimes require hospitalization. Infants, young children and disabled or elderly people who are unable to care for themselves are particularly susceptible to becoming dehydrated. Also, people who are immune-compromised risk dehydration because they may experience a more serious illness, with greater vomiting or diarrhea. They may need to be hospitalized for treatment to correct or prevent dehydration.

How the Norovirus is Spread

Norovirus is spread when the feces or vomit from an infected person is transferred to another person. This most often occurs by person-to-person contact but the following environments also support the spread of illness:

  • Food Preparation - Food does not create the virus but becomes contaminated when an ill person handles food. An infected person can easily shed norovirus particles onto food and work surfaces. It only takes a small number of particles (fewer than 100) to contaminate food. People who have the norovirus illness are capable of shedding billions of particles. Similarly, foods can become contaminated when placed on counters or surfaces that have the infectious particles on them.
  • Natural Environment - It is possible for fresh foods to become contaminated in their natural environment. For instance, shellfish that are harvested in polluted waters can become contaminated. Oysters are particularly problematic because they are often served raw or quick steamed. Noroviruses are relatively heat resistant and can survive temperatures as high as 140°F. So quick steaming, a process that is common when cooking shellfish, may not be adequate to kill the virus. Fruits and vegetables can become contaminated with norovirus in the field, where they are grown and harvested. The failure to thoroughly clean and/or cook contaminated produce before consumption can cause illness.  
  • Waterborne Outbreaks - Sewage contamination of wells and recreational water in communities has been known to cause the norovirus illness to spread.  

It is very common for a norovirus outbreak to occur in community settings. Common locations include: restaurants, catered events, nursing homes, day-care facilities, schools, vacation sites and cruise ships. This virus is very contagious and can spread rapidly throughout these environments. Workers in day-care centers and nursing homes should pay special attention to children or residents who have the norovirus illness. Restaurant workers and caterers who have been sick should not prepare food for others for at least 3 days after recovery.

People infected with the norovirus are contagious from the moment they begin feeling ill. They will remain contagious for a minimum of 3 days and up to two weeks after illness.

Medical Treatment for Norovirus

Currently there is no antiviral medication available to inhibit the development of norovirus, there is no vaccine to prevent infection and the infection cannot be treated with antibiotics. The most significant treatment for norovirus is to prevent dehydration (the loss of fluids). Dehydration is the most common health affect developed from the norovirus infection and can be serious for young children, the elderly, and people with a compromised immune system. Fluid replacement should begin at home with the onset of symptoms. Drinking oral rehydration fluids (ORF), juice or water can reduce the chance of becoming dehydrated. For specific information on rehydration fluids that are best suited for you, contact your physician. Additionally, The Centers for Disease Control (CDC) recommends that families with infants and young children keep a supply of oral rehydration solution (ORS) at home at all times and use the solution when diarrhea first occurs in a child. ORS is available at pharmacies without a prescription. Follow the directions on the ORS package and use clean or boiled water. Medications, including antibiotics (which have no effect on viruses) and other treatments, should be avoided unless specifically recommended by a physician.

Prevention of the Norovirus

You can reduce the chance of getting infected with norovirus by practicing extra strict cleansing. Frequent hand washing, prompt disinfection of contaminated surfaces and immediate washing of soiled clothing will help control the spread of the virus. Norovirus is resistant to normal sanitation solutions so a chlorine bleach solution that contains 5-25 tablespoons of household bleach (5.25%) per gallon of water is required to eliminate the pathogen on surfaces that have been exposed to fecal matter or vomit. Avoid food or water that is thought to be contaminated. Sanitize cutting boards and other food surfaces as needed with 1-teaspoon liquid chlorine bleach per quart of water. Immediately remove and wash clothing or linens that may be contaminated with the virus after an episode of illness (use hot water and soap).

People who are infected with the norovirus should not prepare food or care for others while they have symptoms and for three days after they recover. Food that may have been contaminated by an ill person should be disposed of properly.

Proper Hand Washing:

  • Wet hands thoroughly with warm water.
  • Apply soap generously.
  • Rub hands for at least 20 seconds.
  • Scrub under nails with a clean nailbrush.
  • Rinse hands well with warm water.
  • Dry hands using a clean paper towel.

Norovirus & the CDC

For more information on norovirus including current outbreaks and emerging strains, visit the norovirus information site at the Centers for Disease Control and Prevention (CDC) http://www.cdc.gov/norovirus/

Sources:

  1. Centers for Disease Control and Prevention, http://www.cdc.gov/norovirus/
  2. Ranking the Risk: The 10 Pathogen-Food Combinations with the Greatest Burden on Public Health. M.B. Batz, S. Hoffman and J.G. Morris, Jr. April 28, 2011. University of Florida Emerging Pathogens Institute.   http://www.epi.ufl.edu/sites/www.epi.ufl.edu/files/RankingTheRisksREPORT.pdf
  3. National Institute of Allergy and Infectious diseases, http://www.niaid.nih.gov/topics/norovirus/Pages/symptoms.aspx

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