By Imogen Foulkes BBC News, Bern

The campaign is running on TV, in cinemas and on billboards

A new public health campaign in Switzerland is raising eyebrows.

The campaign, from the Federal Health Office's Aids prevention section, features fencers and ice hockey players enthusiastically pursuing their sport.

But there is one unexpected difference - all the players are stark naked.

The contrast of healthy flesh and sharp blades is supposed to hammer home the message "no action without protection".

The campaign is now running on television, in cinemas and on billboards around the country.

The advertisements are certainly attracting attention, and that is exactly what the Federal Health Office wants.

"We want to tell people that, just like ice hockey or fencing, you don't have sex naked," says Roger Staub, head of Aids prevention. "You should wear a condom."

History of controversy

This campaign is just the latest in a long line of controversial Aids prevention messages in Switzerland.

Haven't you forgotten something? That's it, your condom Previous campaign catch line

A few years ago the health office focused on adultery, telling those who were tempted to stray from their long-term partners that infidelity must always be accompanied by a condom.

Then there was the campaign that targeted different groups in Swiss society such as business leaders, politicians and army officers.

"Haven't you forgotten something?" was the catch line. "That's it, your condom."

There were posters at the border informing tourists of Switzerland's speed limit on the motorways and a suggestion that condoms were obligatory too.

Hotels were even advised to put condoms next to the Bible on bedside tables.

It is a very non-judgemental approach from the country that brought the world Calvinism, but Roger Staub says he is not out to court controversy.

"We don't set out to annoy people with our campaigns," he says.

"Nevertheless we think it's good if people talk about them, and we're certainly not afraid of controversy."

Worrying signs

Switzerland began its upfront Aids prevention campaigns for good reason.

I'm less worried about the ones who know the situation - they've made a conscious choice - than the ones who don't know Roger Staub, head of Aids prevention

In the late 1980s and early 1990s the Swiss had the highest HIV infection rate in Europe, partly because of high intravenous drug use, and partly because the wealthy Swiss were frequent travellers in countries where Aids was already well-established.

The prevention campaigns, together with a vigorous policy of needle exchange and even heroin prescription for long-term drug users, have brought the infection rate down.

But with the success of anti-retroviral drugs there are worrying signs that many people are becoming complacent.

A recent study by the university of St Gallen showed that of more than 700 people infected with HIV since July last year, 80% knew how they were infected and more than half even knew exactly when.

Last year's Aids Day was marked at the parliament in Bern

More worrying still, most knew their partner was HIV positive, but 20% chose to have unprotected sex anyway.

"There are some people who just don't care," says Mr Staub.

"We live in a society where if you want to kill yourself you can. I'm less worried about the ones who know the situation - they've made a conscious choice - than the ones who don't know."

Nevertheless the Federal Health Office says HIV rates among heterosexuals and among drugs users are coming down, a sign that most people are paying attention.

But among Switzerland's gay community the message does not seem to be getting across. New infections rose by 34% last year.

"This is very worrying," says Mr Staub. "If a gay man meets another gay man tonight, the risk that one of them is already HIV positive is more than 10%."

"And clearly some are not using protection - that is why we are seeing more new infections."

So are there new campaigns in mind that will target the gay community specifically?

"Every year we have a campaign which targets the gay community, this year will be no exception," says Mr Staub.