What's more, people who know this option is available to them don't appear to be more likely to engage in risky behavior, said Dr Steve Shoptaw of the UCLA Department of Family Medicine in Los Angeles, who was involved in the research.
"This is a viable way of helping people stay HIV-negative," he said.
So-called post-exposure prophylaxis, or PEP, has long been available to people who risk HIV infection on the job, for example a health care worker accidentally jabbed by a contaminated syringe.
PEP still not widely used despite benefits
In 2005, the Centres for Disease Control and Prevention expanded its PEP guidelines to cover people exposed to HIV outside the workplace, for example through risky sex, condom breakage or drug use.
But PEP still isn't widely used in such cases, Shoptaw and his team note, because it isn't covered by health insurance and is only very rarely offered as part of community health programs.
To investigate the feasibility of a community organised and funded non-occupational PEP program, the researchers conducted a demonstration project in which people were offered a 28-day course of anti-HIV drugs within 72 hours of potential exposure to HIV.
How the study was done
One hundred people, 95 of them men, participated.
They received the drug treatment, HIV testing, and counselling for up to 26 weeks after enrolling in the study. Fifty-eight participants reported having unprotected anal sex, while 18 percent reported condom breakage.
Among the 84 people given the full course of medication, 75 percent actually took all the drugs. No one became HIV-positive during the course of the study.
Some authorities reluctant to offer PEP
Some health authorities have been reluctant to offer PEP after risky sex or drug use for fear that people wouldn't change their behaviour if they knew "there's a parachute somewhere they can take to stay negative," Shoptaw noted.
However, he and his colleagues found people reduced their risk behaviour after using PEP, rather than increasing it.
He and his colleagues call for making non-occupational PEP programs more widely available to people who are at high risk of becoming infected with HIV.
For now, Shoptaw noted, PEP is available only to people who can access it and pay for it out of pocket - drugs and counselling together cost about $2 200 (roughly R15 000).
"Right now, this is more of a social justice issue," Shoptaw said. "People who have means have access to this, but those without means don't have access." – (Reuters Health)
Read more:
Medical schemes, HIV/AIDS and the government
New weapons in AIDS war