Why is norovirus suddenly in the headlines?
Because it is a disease that peaks in the winter, and this is the middle of winter. There is also some evidence that this year it is affecting even more people than usual. It’s not an epidemic, but 2007-08 may turn out to be the worst year for norovirus since, well, 2006-07.

Hang on, didn’t I read it was the worst since 2002?
That claim has been reported. But what is actually the highest since 2002-03 is the rise in infections before the end of the calendar year. Infections have risen faster and earlier this winter than in any since 2002-03, but that doesn’t mean that the total will be higher.

I’ve never even heard of it before and suddenly it has shut dozens of wards. That must be cause for alarm?
The virus responsible has had lots of names, and only relatively recently have doctors settled on norovirus. Previously it has been described as the “Norwalk-like virus”, the “winter vomiting virus”, and the “small round structured virus”, so it is not surprising that name recognition is low.

In the past, it generally hit the headlines when it caused embarrassing outbreaks of diarrhoea and vomiting on cruise liners.

How serious is the disease?
It’s unpleasant rather than serious. It causes diarrhoea, vomiting and fever, but it resolves without treatment in two to three days. Sometimes the symptoms can include projectile vomiting, which obviously increases the risk of spread, especially in closed communities such as hospitals, care homes and cruise liners. It needs no treatment, and seldom causes complications. Paracetamol for the fever and lots of fluid to prevent dehydration are the only recommended treatments.

Is it a superbug?
Happily, no. But it is a virus, so antibiotics are not effective against it. There are no antiviral drugs that work, nor is there a vaccine to protect against it. Developing a vaccine is tricky because there is little evidence that suffering the infection once protects against future attacks. There are many different types of norovirus and getting one does not protect against others. However, there are some efforts afoot to produce a vaccine.

How common is it?
Extremely common. The Centres for Disease Control in the US believes that it may be responsible for half of all food-poisoning cases. In the UK, the Health Protection Agency (HPA) estimates that it causes 600,000 to one million cases in a typical year.

Is it increasing?
The year-by-year data collected by the HPA would suggest that, at first glance. They collect only laboratory-confirmed cases of norovirus infections, which have risen from a few hundred in the 1980s to nearly 4,500 in 2006. But there is less in these figures than meets the eye.

Norovirus is not a new infection. It has always been around, but was identified as a common cause of food poisoning only in the 1970s, when Norwalk virus was first isolated after an outbreak of gastroenteritis in a school in Norwalk, Ohio.

Serious efforts to identify the cause of stomach upsets rely on tests that were not available until comparatively recently. And possibly our parents and our grandparents, who were used to much more serious diseases, shrugged off a two-day bout with diarrhoea as pretty trivial.

What this means is that ascertainment of the cause of such upsets is relatively new, so the apparent increase may simply be the result of looking harder.

What is happening to make this winter special?
Norovirus infections seem to have started earlier in the winter, leading to suggestions that this year would see a record number of cases. By the end of November, the HPA had laboratory confirmation of 1,325 cases, the highest at that time of year since 2002, when the corresponding figure was 1,835.

These represent a fraction of cases, perhaps as few as 1 in 1,500. Most people don’t even bother to consult their GPs, and of those who do, few samples are sent for analysis. So this figure may mean something, or nothing. It may simply mean that norovirus is peaking earlier this year, and the outbreaks will shift in time without increasing in size.

But aren’t hospitals closing a lot of wards and NHS Direct taking a lot of calls?
Yes, GPs in some areas are reporting a lot of cases. But norovirus infections are minor, so there is no obligation to report them, or to gather up-to-date statistics. It is a far less serious disease than flu, for example, for which figures are gathered weekly by the Royal College of General Practitioners from 100 sample GP practices in Britain.

So claims that two million people have fallen ill with norovirus so far this winter are a guess. We simply don’t know. In 2002, when the rise in laboratory reports was early and swift, the total number of reports for the whole year was in fact less, at 4,308, than it was in 2006 (4,446), when nobody made the slightest fuss about norovirus.

What about ward closures?
First, they aren’t actually closures. Nobody is drawing the blinds, closing the doors and leaving wards empty. What is happening is that wards are being closed to new admissions. If there is an infection in a ward, it makes no sense to admit patients to it. But removing those who are already there would be shutting the stable door after the horse has bolted, and risk spreading infection to other wards.

The BBC reported that 56 wards had been closed, which is possible. The issue is whether this is exceptional for this time of year. In general the closures involve a small proportion of the beds, and no central records of closures are kept by the Department of Health. So we simply don’t know if this is unusually high. Many doctors believe it is, but without statistics such claims need to be treated cautiously.

So it’s a storm in a teacup?
Nobody wants to diminish the suffering of people whose Chistmas was disrupted by projectile vomiting. But it’s important to retain perspective. Norovirus infections don’t kill, or seriously discomfort, most of those who get them. They feel rotten, and then recover. In the great scheme of things, the disease is no worse than a pimple, or a cold sore – irritating but unimportant.

So why have we heard so much about them this winter?
Christmas is an almost endless, news-free break. My guess (and it’s no more than that) is that some newspaper executive, somewhere, suffered a bout of gastroenteritis and decided it was a national issue. Since then, rather like the symptoms of the disease itself, it has run and run. But keep calm and it will soon clear up.

Explore Health

• Expert Advice

• Health Features

• Mental Health

• Alternative Medicine

• Child Health

• Health Club