The study, which was carried out among 1,500 factory workers in Ethiopia and started in 1997, showed a marked drop in casual sex and an increase in condom use. Prevalence rates of the virus also plummeted.
Dr Yared Mekonnen, of the Ethiopian Health and Nutrition Research Institute, told IRIN that HIV testing should be promoted across Africa.
"At the beginning, risky sexual behaviour was quite common among these people," Dr Yared said. "Most of them have extra marital sex, they go to sex workers and condom use is very low in this group. Sexually transmitted diseases are also very common."
Every six months, the researchers collect details from the factory workers and take blood samples to test the prevalence of HIV/AIDS.
Dr Yared said through interventions such as voluntary counselling and testing programmes, their behaviour changed dramatically.
Tests now show a new infection incidence rate of 0.4 per 100 per year, compared to five years ago when it was three times as high.
The researchers said education programmes and condom distribution at the factory had also played a role.
"The knowledge of HIV in this country is very high but behavioural change is a very hard issue, so the only way to change their behaviour is to promote voluntary testing and counselling," Yared pointed out.
HIV/AIDS has had a catastrophic affect on Ethiopia with some 3.5 million people living with the virus - the third highest infected population in the world.
Some one million children have also been orphaned while overstretched health services have been pushed to the limit.
Yared said that surveys in Ethiopia revealed that one in five people have extra marital sex, but added that in their survey group it was now almost negligible.
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