Noroviruses - which are often mistakenly called `stomach flu’ - are single-stranded RNA viruses that (like influenza) are able to evolve rapidly. Victims usually experience nausea, frequent vomiting & diarrhea, and stomach pain – and may also suffer from headache, fever, and body aches.
We typically see a new dominant norovirus strain emerge every two or three years. In 2009, we saw the emergence of the New Orleans strain of GII.4, while in 2012, the Sydney strain appeared.
Outbreaks from these viruses are the bane of cruise ships, schools, and hospitals – anywhere large numbers of people congregate. While the illness usually runs its course in 1 to 3 (very long) days - among those who are aged or infirmed -the virus can take a heavy toll.
According to the CDC, in the United Sates each year the norovirus:
The `standard’ mode of norovirus transmission is considered to be the fecal-oral route, but limited airborne transmission is increasingly viewed as an important factor as well (see CID Study: Airborne Norovirus In Healthcare Facilities).
- 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
All of which serves as prelude to a report out of the University of New South Wales where they've identified not one - but three - new emerging strains of Norovirus in Australia.
UNSW scientists have identified three new strains of highly contagious norovirus that are responsible for a major new epidemic of viral gastroenteritis that has affected hundreds of thousands of Australians over winter.Whether any of these emerging strains will spread as rapidly and as widely as the 2012 Sydney GII.4 strain remains to be seen, but the timing is right for seeing a new strain take hold.
Scores of outbreaks of nausea, vomiting and diarrhoea have occurred in Sydney, the Hunter region and the ACT, mainly in closed settings including aged care facilities, hospitals, childcare centres and cruise ships. More cases are expected.
In 2012, Professor Peter White and his team in the UNSW Faculty of Science discovered a new strain of norovirus named Sydney 2012, which caused a worldwide pandemic of gastro, including major outbreaks in Australia.
This strain dominated cases of norovirus infection until this year, when it declined from 75 per cent of cases to 18 per cent of cases in Australia. Similar trends have also been seen in the US and New Zealand.
“Now that Sydney 2012 has declined, three new strains of norovirus have emerged as a new major health concern," says Professor White.
“They are responsible for a big increase in the number of gastro cases in Australia in the past two months, and this new spate of infection is likely to continue to cause a wave of sick leave that will affect businesses and schools already reeling from the effects of the current influenza epidemic.”
UNSW PhD student and molecular virologist Jennifer Lun worked out the genetic typing of the new viral strains.
“I was surprised to find three new viruses, rather than a single one,” she says.
“Two of the viruses are hybrid strains that evolved from the previous pandemic Sydney 2012 strain, while the other new strain is likely to have come from Asia. It occurred to me immediately that there was a potential for them to cause an increase in outbreaks this winter, because people have not been exposed to them before.”
Each year, norovirus infects about two million Australians and kills about 220,000 people worldwide. The nausea, vomiting and diarrhoea usually last for two to three days.
“Norovirus is highly infectious and can spread through aerosol particles when people vomit," says Professor White, of the UNSW School of Biotechnology and Molecular Sciences.
“During the past 20 years there have been six global epidemics of norovirus, in 1996, 2002, 2004, 2006, 2009 and 2012. Only time will tell how widely these three new strains will spread.”
The three new strains are called Kawasaki 308, New Orleans 2009/Sydney 2012 and GII.P16/Sydney 2012.
The research on the new strains was carried out in collaboration with researchers at the Prince of Wales Hospital, Westmead Hospital, Canberra Hospital, the NSW Public Health Unit and medical testing service Douglass Hanly Moir.
Professor White established the Australian and New Zealand Norovirus Surveillance Network of testing laboratories in 2006, which has links with two similar organisations in Europe and North America to form a global surveillance network.
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.