Low condom use, needle sharing and a rise in casual sex and prostitution may unleash an HIV epidemic in the Philippines, according to a new study.

The report, published in the Journal of the International AIDS Society, said young adults, gay and bisexual men, prostitutes, injecting drug users, overseas Filipino workers and sex partners of all these groups were vulnerable to contracting the virus.

"There is no guarantee that a large HIV epidemic will be avoided in the near future. Indeed, an expanding HIV epidemic is likely to be only a matter of time as the components for such an epidemic are already present in the Philippines," wrote Anna Farr and David Wilson at the National Center in HIV Epidemiology and Clinical Research at the University of New South Wales in Sydney.

Unlike other countries in the region, the spread of HIV in the Philippines has been described as "low and slow" because of a disperse geography, relatively uncommon intravenous drug use, sexual conservatism and high male circumcision rates.

But the authors said an HIV epidemic was possible because of the presence of many conditions "for a large, increasing and generalized epidemic."

"These include: a low rate of condom use; unsafe practices among intravenous drug users; large migration rates; increasing trends in extramarital and premarital sex; a lack of education and common misconceptions about HIV/AIDS; and cultural factors that inhibit public discussion of issues of a sexual nature," they wrote.

The report also focused on the 7.5 million Filipinos working abroad in 170 countries.

"By participating in casual unprotected sex or other risky behavior while overseas in higher prevalence settings, overseas Filipino workers become a substantial source of new HIV cases in the Philippines upon their return home," they said.

Overseas Filipino workers make up 30 to 35 percent of all HIV cases reported in the country, the report said.

The Philippines has the lowest rate of condom use in Asia - just 20 to 30 percent among groups at risk of HIV infection such as sex workers, according to the report.

"A common perception is that condoms are only for birth control and not for protection against HIV and other sexually-transmitted illnesses," the authors wrote.

"This perception is reinforced by the view that condoms are discouraged by the Roman Catholic Church. Government family planning programs have policies against supplying condoms to unmarried people."

Monthly HIV diagnoses among homosexual men jumped to 704 by 2008 from 328 in 2003, while the figure among bisexual men shot to 289 from 92 within the same period. The average age of diagnosis has also fallen significantly, from 36 before 2005 to 29 years recently, the authors wrote.