Thursday, January 24, 2013

MMWR Report On New Norovirus GII.4 Sydney Strain

norovirus 3D structure

Norovirus – Credit HPA



# 6878


Regular readers of this blog are aware that we’ve paid more attention this year to norovirus than in previous years, simply because there’s a lot of it going around this winter.


In Eurosurveillance: Emergence & Spread Of GII.4 Variant Norovirus, we looked at early indications that a new variant of Norovirus was on the rise in Europe, and around the world.  


A few days later, I carried comments by the man who discovered this new strain - Professor Peter White, and his team in the School of Biotechnology and Biomolecular Sciences – see (UNSW: Sydney 2012 Norovirus Rising).


Noroviruses, which are often mistakenly called `stomach flu’, are single-stranded RNA viruses that are able to evolve rapidly, so we typically see a new dominant norovirus strain emerge every two or three years.


Victims usually experience nausea, frequent vomiting & diarrhea, and stomach pain – and may also suffer from headache, fever, and body aches.


The illness generally runs its course in 1 to 3 (very long) days, and most people recover. But among those who are aged or infirmed, the virus can take a heavy toll. 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


Today the CDC has confirmed what many have suspected; that this new Sydney strain of norovirus is contributing heavily to this year’s norovirus season here in the United States.


In a press release mailed out today, the CDC previewed today’s MMWR report:

New norovirus strain causing most norovirus outbreaks in United States

Not yet known if strain will cause more outbreaks than previous years


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 Centers for Disease Control and Prevention. 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 through CaliciNet 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



A link to and excerpt from today’s MMWR.


Notes from the Field: Emergence of New Norovirus Strain GII.4 Sydney — United States, 2012


January 25, 2013 / 62(03);55-55


GII.4 noroviruses remain the predominant cause of norovirus outbreaks, and the GII.4 Sydney strain appears to have replaced the previously predominant strain, GII.4 New Orleans. Compared with other norovirus genotypes, GII.4 noroviruses have been associated with increased rates of hospitalizations and deaths during outbreaks (5). Health-care providers and public health practitioners should remain vigilant to the potential for increased norovirus activity in the ongoing season related to the emergent GII.4 Sydney strain.


Continued surveillance for norovirus outbreaks through CaliciNet and additional data on clinical and epidemiologic features of outbreaks collected through the National Outbreak Reporting System (NORS)§ will enable further assessment of the public health implications of the new GII.4 Sydney strain, including any association with increased severity or level of activity in the ongoing 2012–13 winter norovirus season. Proper hand hygiene, environmental disinfection, and isolation of ill persons remain the mainstays of norovirus prevention and control (1).



One of the keys to prevention is good hand hygiene, unfortunately, unlike with many other bacteria and viruses, alcohol gel doesn’t do a particularly good job of killing the virus (see CMAJ: Hand Sanitizers May Be `Suboptimal’ For Preventing Norovirus).


The CDC offers this advice to help prevent the spread of this virus.



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