Winter vomiting virus

"Winter vomiting" is usually non-fatal, but dramatic

The winter vomiting virus causes unpleasant but non-fatal infections that last only a few days.

Even the elderly and frail are likely to make a full recovery after contracting the illness.

The SRSV family of viruses, also referred to as Norwalk or Norwalk-like viruses, produces a gastro-enteritis illness.

It is dubbed the "winter vomiting virus" because it is more likely to develop as an illness during the winter months.

The bug hit the headlines in the UK in January 2002, when there was an outbreak in Scottish hospitals.

Projectile vomiting

The illness typically starts with an attack of vomiting - which can of the severe, projectile variety.

A patient can go from feeling fine to severe vomiting in a very short period.

Some patients also experience diarrhoea.

It's a very clever virus - it gets around, and it is pretty good at spreading itself

Professor Hugh Pennington

Dr John Cowden, consultant epidemiologist at the Scottish Centre for Infection and Environmental Health in Glasgow, said: "We are not talking about feeling a bit dicky and chucking up in the toilet bowl.

"I am told that people can vomit straight out for about a yard."

There is no recognised treatment for the illness - patients should be given fluids to keep them hydrated and wait for it to pass.

It normally does so in 24-60 hours in the vast majority of patients, although there may be some after-effects such as fatigue.

There were approximately 2,000 cases of SRSV reported to the Public Health Laboratory Service in 1999 - but the total number of infections which go unreported is many times this.

Highly infectious

Many cases are the result of food poisoning - "bad mussels" can be a potent source of SRSV.

It is usually caught either through faecal waste contamination, or by being near someone who is vomiting.

It is estimated that 30m particles - only six to 10 are needed for an infection - may be sent into the air during a vomiting attack, creating the potential for rapid spread.

The virus can lie dormant in the human digestive system for months on end before becoming infectious.

Patients may even become infectious before they get ill, although this is not proven.

They stay infectious for 48 hours after symptoms develop.

Hospital workers are particularly at risk of passing it on as they clear up after infected patients, and guidelines suggest stringent disinfecting procedures in the event of illness.

Professor Hugh Pennington, an expert in disease at Aberdeen University, described SRSV as the "Mike Tyson" of viruses.

"It's a very clever virus. It gets around, and it is pretty good at spreading itself."