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Fact Sheet: Norovirus in Schools

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Noroviruses are a group of viruses that cause gastroenteritis (GAStro-en-ter-I-tis), in people. Norovirus is known incorrectly as the “stomach flu”. Norovirus is NOT related to the flu (influenza), which is a respiratory illness caused by a different virus. The term norovirus was recently approved as the official name for this group of viruses; previously it had been referred to as “Norwalk virus” or “Norwalk-like virus.”



Norovirus is spread when material contaminated by stool or vomitus from an infected person is ingested. Norovirus is extremely infectious. It takes only a few particles, so small that they cannot be seen with an ordinary microscope, to cause illness. Millions of particles are present in the stool or vomitus of someone who is sick. Excretion of virus in stool begins a few hours before the onset of symptoms and reaches amaximum 24-72 hours after exposure. The virus may continue to be present in the stool of infected persons for a week or more, even after they recover, but people are most infectious up to 48 hours after symptoms resolve. The virus is spread primarily through contamination of the hands of person who are ill. Good hand washing with soap and water is essential. Hand sanitizers are not effective in killing the virus. Vomiting will also suspend viral particles in the air, resulting in contamination of the environment. Norovirus can remain infectious on environmental surfaces for many days and are relatively resistant to disinfection, heat and cold.



Yes, norovirus can also be transmitted by food and water. Food preparers or handlers who have norovirus may contaminate food, especially if they do not wash their hands regularly after using the bathroom or do not wear gloves while handling food. Cold foods such as salad and sandwiches have been a source for outbreaks. Drinking water can also be contaminated due to faulty plumbing and be a source of these viruses.



Norovirus cannot be diagnosed by traditional stool cultures or examination of stool for ova and parasites. Norovirus can be identified by a method called polymerase chain reaction (PCR). This requires fresh refrigerated (unfrozen) stool. PCR can remain positive for at least a week after the symptoms have resolved. While PCR can be completed within a day or two of receiving 4-10 stool specimens, decisions to institute control of a possible outbreak should not be delayed while waiting for results.



Schools should establish and maintain a program of surveillance for norovirus illness. An outbreak of norovirus should be suspected when two or more students in one classroom and/or staff have vomiting and diarrhea with onset within one to two days. Vomiting, often projectile, is present in at least half of those ill. Other symptoms may include nausea with or without vomiting and lowgrade fever.



Interrupting person-to-person transmission controls the outbreak of norovirus. The following recommendations may assist school personnel in controlling an outbreak of norovirus.

  1. Limit transmission when initial cases of norovirus are suspected.
    1. Notify the Principal
    2. Confine symptomatic students to a room or segregated area until they can leave.
    3. New cases should be recorded daily.
    4. Notify the local health department (513-946-7923) and consult with them about laboratory testing and control of the outbreak.
  2. Institute control measures when a norovirus outbreak is suspected.
    1. Minimize movement of students.
    2. Persons experiencing symptoms should not be involved with food preparation or food handling.
    3. Students and staff experiencing symptoms should not attend school until 48 hours after symptoms have stopped.
    4. Limit group gatherings until the incidence of new cases has reached zero.
    5. Increase frequency of cleaning bathroom and shared common areas. Consider the use of respiratory protection for cleaning staff where aerosols may be present following vomiting, or be generated by cleaning activity.
      1. Clean and disinfect vomit and fecal spillages promptly.
      2. Use an Environmental Protection Agency-approved disinfectant or a freshly prepared sodium hypochlorite solution (household chlorine bleach in a 1:100 {500ppm} to 1:10 {5,000ppm} dilution) to disinfect surfaces contaminated with feces or vomitus. Doorknobs, light switches, handrails should also be disinfected.
      3. Metal chairs/desks and stationary furniture residing in classrooms of persons who have been vomiting should be washed with disinfecting solution.
      4. All bathroom surfaces, including floors, should be disinfected.
      5. Clean carpets and soft furnishings with hot water and detergent or steam clean. Dry vacuuming is not recommended.



For more information contact the Disease Prevention Division at 513.946.7849 or 7887.


Download a printable version of this fact sheet here.


250 William Howard Taft Road
2nd Floor, Cincinnati, OH 45219
Phone 513.946.7800 Fax 513.946.7890