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Delaware Health Alert Network #286

December 3, 2012 8:37 am

Health Advisory

The Delaware Division of Public Health (DPH) is issuing this health advisory to provide healthcare providers with information regarding a potential increase in acute gastroenteritis associated with norovirus and recommendations for testing patients with gastroenteritis.


In March 2012, a new norovirus variant was identified in Australia. Through national laboratory surveillance, the Centers for Disease Control and Prevention (CDC) reported that this norovirus variant has been associated with outbreaks occurring in the United States (U.S.). There is a potential for the circulation of this new norovirus variant to lead to an increase in acute gastroenteritis in Delaware and across the country.


Norovirus is the leading cause of foodborne illness in the U.S., responsible for about 21 million cases of acute gastroenteritis, 70,000 hospitalizations, and 800 deaths annually.  Noroviruses are a group of viruses that cause gastroenteritis marked by an acute onset of severe vomiting, watery diarrhea, and nausea, which occurs 12 to 48 hours after exposure to the virus and lasts 24 to 72 hours after onset of symptoms. Noroviruses spread very rapidly. Young children, the elderly, and people with other medical conditions are at highest risk for severe or prolonged infection. Norovirus illness often occurs during the winter months. Shedding of the virus (peak: 2-5 days after onset) occurs primarily in stool but also in vomitus and is transmitted by contaminated food/water, person-to-person, fomites, and aerosols (from vomiting). There is no specific therapy for norovirus infections available aside from supportive care.

Healthcare facilities (including long-term care facilities) and other institutional settings such as daycares and schools are particularly at risk for outbreaks because of increased person-to-person contact. Most foodborne outbreaks of norovirus illness are caused by eating food contaminated by a food handler. However, outbreaks of norovirus can also be caused by food such as oysters, raspberries, and leafy greens that were contaminated at their source.

In addition to concerns regarding the circulation of this new variant of norovirus, healthcare providers may want to consider ordering stool culture and Norovirus PCR tests for any patient with signs/symptoms of gastroenteritis who works in (or attends/is a resident of) a sensitive environment (e.g. food establishment, hospital, daycare, school, or others as determined by the attending healthcare provider) in which this organism can be readily spread to at-risk populations.

Given the potential for an increase in acute gastroenteritis associated with norovirus and to prevent the spread of the virus and reduce the burden of the disease on high-risk populations, DPH is providing the following guidance.

Some Key Points on Norovirus

  1. The virus is shed primarily in stool but also found in vomitus.
  2. Peak shedding is 2-5 days after onset.
  3. Viral load of ~100 billion viral copies/gram of feces --- exposure to as few as 18 viral particles sufficient for infection.
  4. Transmitted by contaminated food/water, person-to-person, fomites, aerosols (from vomiting). Secondary spread is common.
  5. Incubation period averages 24-48 hours.
  6. Duration is typically short; repeat infections common.
  7. Disease can be more severe in the elderly.
  8. No specific therapy available; supportive care only.
  9. Long term care facility outbreaks can be prolonged, sometimes lasting many weeks
  10. If testing is performed, stool is preferred over vomitus; whole stool is preferred over rectal swabs.
  11. Virus can be found in stool up to 2 weeks after onset but optimal to collect stool within 24-72 hours of onset.


For patients presenting with signs/symptoms of gastroenteritis (e.g. vomiting, diarrhea, etc.) who are in sensitive occupations or environments such as those listed below:

  1. Food handlers (e.g. work in a food establishment)
  2. Healthcare workers
  3. Residents of long-term care facilities
  4. Attend or work in other institutional settings (e.g. daycares, schools, etc.)
  5. Or other patients who may readily transmit a potential organism to an at-risk population, as determined by the attending healthcare provider.

Healthcare providers may want to consider requesting the following laboratory tests:

  1. Norovirus PCR
  2. Stool culture (for identification of bacterial pathogens)

Additional Information


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