The number of new HIV infections among gay and bisexual men in Switzerland has almost doubled over the past three years.
In a report published on Monday, the Federal Health Office said it was concerned by this trend and intended to focus greater efforts on its HIV/Aids prevention programmes.
In Switzerland three out of every 1,000 people are living with HIV/Aids. Over the years better prevention has reduced infection rates among drug users and immigrants, but since 2000 new HIV infection rates among gay and bisexual men have continued to rise.
In 2005, 49.3 per cent of all men diagnosed as HIV-positive were gay or bisexual, whereas they represented 36.5 per cent in 2004. And by the end of 2006, the Federal Health Office expects 300 new cases.
Yet according to the authorities this is a phenomenon that other western European countries are also having to come to terms with.
There are many reasons for this increase, according to the Federal Health Office.
"Many gay and bisexual men in Switzerland have dropped their guard," it explains. It is felt that large numbers are tired of the prevention messages that spoil the party atmosphere of certain evenings.
Also, improvements in anti-retroviral treatments allowing those who test positive for Aids to live longer have deluded people into thinking that Aids is an illness that can be treated.
The Federal Health Office also highlights the growth in internet chat sites, which enable people to meet up in non-traditional locations away from saunas and sex clubs which are targeted by prevention campaigns.
According to a study by the gay association Dialogai, in general higher numbers of gay people suffer from anxiety, drug addiction, alcoholism and depression than among the general population.
The Federal Health Office concludes that depression, even temporary, can "cause a person to take higher risks when meeting someone, despite their knowledge about HIV and initial wish to have protected sex".
To tackle "this serious epidemic", the Health Office has invited groups representing gay and bisexual men to refocus their efforts on HIV prevention. Rather than wishing to change existing campaigns, the office wants to ensure that all organisations combating HIV/Aids for this particular target group apply the same approach.
swissinfo with agencies
According to the Swiss Aids Federation, more than 20,000 men and women live with HIV/Aids in Switzerland. Two people are diagnosed HIV-positive every day.
Between 1983 and 2005, 8,251 people were diagnosed with Aids, of whom 298 in 2004 and 234 in 2005.
To date, 5,622 people have died from Aids in Switzerland.
65 million people worldwide have contracted Aids since June 1981 and 25 million have died from the disease.
There are more than 38 million people living with HIV. 2.8 million people with HIV/Aids died in 2005, most of them in sub-Saharan Africa.