It's more infectious than HIV, almost as deadly and on the increase. Jerome Burne on hepatitis B, the exotic souvenir you'll want to leave behind
WHAT DO YOU look for when you go on holiday? Sex? Adventure? You know they're risky, in fact that's half the fun, but is it fair to endanger others who haven't chosen the equivalent of white-water rafting in Colombia? That's what you could be doing if you don't get yourself vaccinated against hepatitis B.

"Hepatitis what?" you cry. Just the second most common infectious disease for which there is a vaccination. Worldwide it kills two million people a year, it can give you liver cancer, or destroy your liver to such an extent that you need a transplant. Yet, according to a conference on travel medicine in Venice last month, most people know little about the disease and rarely think of protecting themselves against it. The number of cases in the UK rose last year, and as the holiday season begins a further increase is expected.

You're most likely to catch hepatitis B from unprotected sex or poorly sterilised medical instruments - the needles or scalpels that might be used on you in a third world hospital. It's a blood-borne disease like AIDS, so the sort of behaviour that puts you at risk is much the same.

"Anything that involves swapping of body fluids such as blood or semen can pass it on," says Dr Alan Kitchen of the North London blood Transfusion Centre. "That makes things like acupuncture, tattooing and body piercing risky, too." The good news is that it's not quite as virulent as HIV, the bad is that it is 100 times more infectious. Dried blood with the hepatitis B virus in it can stay infectious for up to a week.

"People do all sorts of things on holiday they would only dream of doing back home," says Dr Jane Zuckerman, an infectious diseases expert at the Royal Free Hospital in London. "We had one case of a man who was on holiday with his family in Benidorm. While they were on the beach, he went and had unprotected sex with a man in the town and got infected." It's this link between hepatitis B and travel that gave the conference its name - "The Accidental Tourist".

Even though 50,000 have the disease in this country, you are most at risk overseas. There are an estimated two billion cases worldwide, mainly in the poorer countries in Asia, South America and Africa. But with the volume of foreign travel set to triple over the next 20 years, the number of people at risk is about to soar. "People are increasingly going to exotic locations, and that often means poor medical facilities" says Henryk Handszuh of the World Travel Organisation. "They also want more adventure and activity holidays and inevitably there are accidents."

At the moment only 13 per cent of travellers visiting high-risk areas have been vaccinated against hepatitis B. This gives rise to the alarming statistic that on an average planeload of 300 people coming back from an area where it is endemic, there will be one person who has just been infected and 17 who have it already. We are all aware of AIDS, but your chances of contracting hepatitis B are far greater. While there are roughly 6 million HIV carriers in the world, hepatitis B has 359 million carriers.

"One of the difficulties we have in getting people to take the disease seriously is that the effects are so varied" says Dr Zuckerman. "Some people catch it, have very mild symptoms and recover completely, but about 10 per cent get it chronically. These are the ones who are constantly infectious and eventually die of it. In fact hepatitis B is second only to smoking as a cause of cancer."

Perhaps the most surprising statistic to come out of the conference is that British women are the least promiscuous in Europe. Or rather, the least likely to have what a survey coyly calls a "holiday romance". The bad girls of Europe, or possibly the most honest, are, amazingly the Swiss. A sample of over 9,000 travellers from nine European countries filled in a questionnaire about their travel habits.

Whereas 20 per cent of Austrians and Swiss admitted to having sex with the locals (males and females in about equal numbers) only three per cent of British females confessed to it, as against 12 per cent of males. The message from the conference was: if you have sex on holiday, wear a condom, even if you lie to the pollsters about it later.