New norovirus variant to blame for outbreak.
Researchers have identified the culprit that ruined holidays, shut down schools and sent millions of Europeans sprinting for the toilet in 2002. The contagious stomach bug was caused by a new variant of a common virus, research reveals.
Two years ago, an infectious bug ripped through schools, hospital wards and luxury liners in Europe and the United States, prompting their closure and quarantine. The offender was a type of norovirus, also known as Norwalk virus, which triggers diarrhoea and vomiting.
Anecdotal reports suggested that the number of outbreaks in 2002 was unusually high, prompting researchers to review the nature and spread of the virus.
So David Brown and colleagues from the Foodborne Viruses in Europe network - a collaborative network of scientists spanning ten countries - analysed the genetic make-up of viral samples from ten different European countries taken between 1995 and 2002.
All of the outbreaks were caused by norovirus, but 2002's problems included a new variant called GII4, the team report in The Lancet1. The new virus is subtly different - one part of one protein has changed. This may make it more virulent, says Brown.
Knowing the virus's genetic make-up may aid vaccine development, he adds. At present, there are no effective vaccines against norovirus. Treatment is limited to fluids and bed rest.
Peak of infection
The team also reviewed the number of outbreaks across the 7-year study period. In England and Wales, 614 outbreaks were reported in 2002 - a 77% increase on the previous peak of 347 outbreaks in 1995. Unusually, many outbreaks occurred during the summer. Similar increases were noted in many other countries, including Hungary, Germany and Denmark.
The virus is unlikely to go away just yet, say the researchers. New variants of the norovirus tend to appear once every five years, says virus expert Carl Kirkwood of the Royal Children's Hospital in Melbourne, Australia. The old ones die away as people build up immunity to them. GII4 has a few more years to go before it is superseded, he says.
The virus, which jumps from infected faeces to the mouth via food or contaminated surfaces, spreads with relative ease. "We're now waiting for it to turn up in Australia," says Kirkwood.
The virus readily infects the very young, the very old and the very sick. Symptoms clear up within a few days, but people can remain infectious for weeks, cautions Kirkwood. During this time, people feel well and return to their daily lives, spreading the infection as they go.
Norovirus is currently on the rise in Virginia and several other American states. It is unclear if the culprit is the same GII4 variant or not.
Koopmans, M. et al. The Lancet, 363, 682 - 688, (2004).