Wednesday, May 09, 2012

Norovirus: The Gift That Keeps On Giving




# 6319



The hallmark of a Norovirus infection is that during the first 12 hours of vomiting and diarrhea you are afraid you might die, and during the second 12 hours you begin to fear you won’t.


While the vast majority afflicted recover, among the elderly and frail this illness can induce serious dehydration and on rare occasions can be fatal.


According to the CDC, each year the norovirus:


  • causes about 21 million cases of acute gastroenteritis (inflammation of the stomach or intestines or both)
  • contributes to about 70,000 hospitalizations and 800 deaths, mostly among young children and the elderly



The CDC maintains an extensive Norovirus webpage where they describe the illness, how it is spread, and how to avoid infection. Among known causes of foodborne illness, norovirus is the largest culprit.



Source CDC


From the Journal of Infectious Diseases today we’ve an epidemiological investigation that examined a norovirus outbreak among a girl’s soccer team and found a common denominator (a reusable grocery bag) and evidence suggestive of aerosol contamination.


In today’s IDSA journal report (and accompanying commentary) we get a fascinating look what may be the `perfect human pathogen’, and how it was easily spread among 17 girls at a soccer tournament in 2010.


First, the press release, then the study:

Public release date: 9-May-2012

Investigators trace of role reusable grocery bag in norovirus outbreak

Oregon investigators recently mapped the trail of an outbreak of a nasty stomach bug among participants in a girls' soccer tournament to a reusable open top grocery bag stored in a hotel bathroom. Their findings, which illustrate the role that inanimate objects can play in spreading norovirus infection, appear in The Journal of Infectious Diseases.


Noroviruses are a leading cause of gastroenteritis worldwide and the most common cause of foodborne outbreaks in the United States. Highly contagious, even in low concentrations, the viruses spread efficiently from feces and vomit by direct contact or by indirect transmission from viral contamination of surfaces. In October 2010, a cluster of gastroenteritis that appeared in a group of people with no apparent direct physical contact with a pathogen challenged investigators to find the cause and take appropriate control measures.


In the study, Kimberly K. Repp, PhD, MPH, of Oregon Health and Sciences University, and William E. Keene, PhD, MPH, of the Oregon Public Health Division in Portland, investigated an outbreak in a group of 17 Oregon girls, 13-14 years old, and their four adult chaperones attending a soccer tournament in Washington state. All had traveled in private automobiles, shared hotel rooms, and eaten at local restaurants. Eight cases were identified, including the index patient who was presumably infected prior to the trip. There was no direct contact between the original patient and her teammates after her symptoms began; before her overt symptoms began she left her room and moved in with a chaperone. The girl subsequently began vomiting and having diarrhea in the chaperone's bathroom. The outbreak affecting the rest of the team began several days later; they were exposed by handling a bag of snacks that unfortunately had been stored in the hotel bathroom. Virus aerosolized within the bathroom likely settled onto the grocery bag and its contents. Matching viruses were found on the reusable shopping bag two weeks later.

(Continue . . . )


A Point-Source Norovirus Outbreak Caused by Exposure to Fomites

  1. Kimberly K. Repp1, and William E. Keene2

The authors describe the route of infection by saying:


Aerosolization of vomit and feces has been demonstrated to be of major importance in norovirus outbreaks [13]. Even viruses aerosolized from flushing a toilet can contaminate surfaces throughout a bathroom [14]. Once a fomes is contaminated, transfer to hands and other animate objects can readily occur [15]. The more confined the space (eg, most bathrooms), the more intense would be the “fallout” [13].


The authors also take notice of some of the lesser known hazards of reusable grocery bags (see my earlier blog It’s In The Bag).


Accompanying this research letter is an informative editorial by Aron J. Hall called:


Noroviruses: The Perfect Human Pathogens?

  1. Aron J. Hall



The role of direct aerosolized human-to-human transmission of norovirus remains a bit murky, although there are numerous anecdotal reports that suggest that it happens.


The CDC – in a an MMWR report from 2011 called Updated Norovirus Outbreak Management and Disease Prevention Guidelines describes transmission thusly:



Norovirus is extremely contagious, with an estimated infectious dose as low as 18 viral particles (41), suggesting that approximately 5 billion infectious doses might be contained in each gram of feces during peak shedding. Humans are the only known reservoir for human norovirus infections, and transmission occurs by three general routes: person-to-person, foodborne, and waterborne.

Person-to-person transmission might occur directly through the fecal-oral route, by ingestion of aerosolized vomitus, or by indirect exposure via fomites or contaminated environmental surfaces.

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