Saturday, January 26, 2013

Norovirus Outbreak: Symptoms and Treatment

More Americans are feeling under-the-weather due to a norovirus strain from the land-down-under, according to the U.S. Centers for Disease Control and Prevention.   

A new strain of norovirus called GII.4 Sydney was the leading cause of norovirus outbreaks in the United States from September to December 2012, according to a study published in Morbidity and Mortality Weekly Report released today by the CDC.  The new strain was detected in Australia in March 2012, and caused outbreaks in that country and several other countries.

CDC researchers analyzed 2012 data collected on norovirus strains associated with outbreaks in the United States. They found that of the 266 norovirus outbreaks reported during the last four months of 2012, 141 were caused by the GII.4 Sydney strain.

“The new strain spread rapidly across the United States from September to December 2012,” said Dr. Aron Hall, epidemiologist, CDC’s Division of Viral Diseases (DVD). “The proportion of reported outbreaks caused by this strain increased dramatically from 19 percent in September to 58 percent in December.” 

Norovirus is very contagious.   In the United States, norovirus is the number one cause of acute gastroenteritis, which leads to diarrhea and vomiting.  Each year, more than 21 million people in the United States get infected and develop acute gastroenteritis; approximately 800 die.  Young children and elderly adults have the highest risk for severe illness.

Norovirus spreads primarily from infected people to others through direct contact.  It also spreads through contaminated food, water, and surfaces.  Norovirus infections are common during this time of the year.  Most outbreaks occur from November to April, and activity usually peaks in January.  Norovirus is also notorious for spreading quickly on cruise ships.

“New norovirus strains often lead to more outbreaks but not always,” said Dr. Jan Vinj√©, director of CaliciNet. Over the past decade, new strains of GII.4 have emerged about every 2 to 3 years. “We found that the new GII.4 Sydney strain replaced the previously predominant GII.4 strain.” 

Better surveillance in the United States and abroad have helped to detect new strains of norovirus sooner, the CDC says.  Early identification of new strains helps to alert the public and health professionals to better prevent infections and control outbreaks.

The CDC advises health professionals to remain vigilant to potential increases in norovirus infection this season due to GII.4 Sydney.  They should follow standard prevention and control measures for norovirus.  People should know that the best ways to help prevent norovirus infection include washing hands with soap and water, disinfecting surfaces, rinsing fruits and vegetables, cooking shellfish thoroughly, and not preparing food or caring for others while ill.

“Right now, it’s too soon to tell whether the new strain of norovirus will lead to more outbreaks than in previous years.  However, CDC continues to work with state partners to watch this closely and see if the strain is associated with more severe illness,” said Dr. Hall.  
According to the CDC, most outbreaks of norovirus illness happen when infected people spread the virus to others.  But, norovirus can also spread by consuming contaminated food or water and touching things that have the virus on them.

Healthcare facilities, including nursing homes and hospitals, are the most commonly reported places for norovirus outbreaks in the United States and other industrialized countries. Nearly two-thirds of all norovirus outbreaks reported in the United States occur in long-term care facilities.

In addition to Healthcare facilities which make up 59% of cases, restaurants are the second top location for outbreaks at 8%, followed by parties and events at 6%.   Cruise ships (4%), schools (4%), and hospitals (4%) account for the remaining known locations.  15% of norovirus outbreak locations are in other or unknown locations.

Outbreaks of norovirus illness have also occurred in restaurants, cruise ships, schools, banquet halls, summer camps, and even at family dinners. These are all places where people often eat food handled or prepared by others.

In fact, norovirus is the leading cause of illness from contaminated food in the United States. About 50% of all outbreaks of food-related illness are caused by norovirus. 

Foods that are commonly involved in outbreaks of norovirus illness are—
  • leafy greens (such as lettuce),
  • fresh fruits, and
  • shellfish (such as oysters). 

The CDC says that the best ways to help prevent norovirus infection include washing hands with soap and water, disinfecting surfaces, rinsing fruits and vegetables, cooking shellfish thoroughly, and not preparing food or caring for others while ill.


Norovirus causes inflammation of the stomach or intestines or both. This is called acute gastroenteritis.  You may hear norovirus illness called "food poisoning" or "stomach flu."  Food poisoning can be caused by noroviruses.  But, other germs and chemicals can also cause food poisoning.  Norovirus illness is not related to the flu (influenza), which is a respiratory illness caused by influenza virus.

The most common symptoms—
  • diarrhea
  • throwing up
  • nausea
  • stomach pain
Other symptoms—
  • fever
  • headache
  • body aches
If you have norovirus illness, you can feel extremely ill and throw up or have diarrhea many times a day. This can lead to dehydration, especially in young children, older adults, and people with other illnesses.
Most people with norovirus illness get better within 1 to 3 days.
Symptoms of dehydration—
  • decrease in urination
  • dry mouth and throat
  • feeling dizzy when standing up
Children who are dehydrated may cry with few or no tears and be unusually sleepy or fussy.


The CDC says tht there is no specific medicine to treat people with norovirus illness. Norovirus infection cannot be treated with antibiotics because it is a viral (not a bacterial) infection.

If you have norovirus illness, the CDC recommends that you should drink plenty of liquids to replace fluid lost from throwing up and diarrhea. This will help prevent dehydration.

Sports drinks and other drinks without caffeine or alcohol can help with mild dehydration. But, these drinks may not replace important nutrients and minerals. Oral rehydration fluids that you can get over the counter are most helpful for mild dehydration.