The number of new cases of HIV and Aids in Singapore fell slightly last year to 454, 15 less than in 2012.
However, the Action for Aids (AfA) group here said there has been a "worrying" rise in infections among homosexual men.
The Ministry of Health revealed the figures yesterday, which also showed that the number of homosexual and bisexual cases has risen from 166 in 2009 to 247 last year.
In contrast, the number of heterosexual men infected fell from 241 to 157 in the same period.
Around a decade ago, men who contracted HIV through gay sex accounted for less than 30 per cent of male infections but they now make up more than 60 per cent - making them the main mode of transmission.
A spokesman for AfA said the rise in homosexual HIV transmission could be because people are not as fearful of contracting the infection as previously due to the availability of effective anti-retroviral medication.
However, he added that there is a degree of "condom fatigue" in Singapore. While surveys show that the rates of condom use have remained steady at about 50-60 per cent, he said this is "unsatisfactory".
The group added that social media has made it easier for people to hook up for casual sex and reduced the age at which many couples first have intercourse.
"We need to review our programmes and reassess our approaches to prevention and care," the spokesman said. "We need to engage and involve at-risk communities at all levels, from policy reviews to programme planning, implementation and evaluation."
The human immunodeficiency virus (HIV) attacks the body's immune system and is transmitted mainly through sexual intercourse, although there are other ways it can spread, such as through sharing contaminated needles or receiving a transfusion of infected blood.
Acquired immune deficiency syndrome (Aids) is the disease caused by HIV.
The MOH figures include both the infection and the disease. In an alert yesterday, it said that 41 per cent of new cases last year were "late stage".
Most of the new cases were men, two-thirds of whom were single.
Almost half the people diagnosed last year found out about their infection when they were in hospital, while one in five discovered it following voluntary HIV screenings.
Since 1985, 6,454 people here have been infected, including 155 diagnosed this year. More than a quarter have died.
Senior Minister of State for Health Amy Khor said: "The number of new infections has remained at about the same level over the last five years."
She said there must be no let-up in education and outreach efforts, adding: "The best way to prevent HIV infection is to remain faithful to one's spouse or partner, avoid casual sex or sex with sex workers and use condoms."
She also urged people in at-risk groups to be screened to allow for early diagnosis.