MELBOURNE, May 23 (Xinhua) -- A Melbourne man has become the third person in the world to test positive for HIV while taking a preventative drug, it was confirmed on Tuesday.
The man, who could not be identified, returned a positive test for HIV despite being a participant in a trial of Pre-Exposure Prophylaxis (PrEP), a drug which has been widely credited to reduce HIV transmission by 99 percent.
It has not yet been confirmed if the man contracted a strain of HIV resistant to PrEP or if other factors are to blame.
There have been two cases of people using PrEP being infected with drug-resistant HIV, one in Toronto and one in New York in 2016.
A spokesperson for the Alfred hospital in Melbourne told reporters that researchers were "reviewing the clinical details of a man who has tested positive to HIV while being a registered participant of the Victorian PrEPX study."
There are 3,000 Victorians enrolled in the PrEP research study, making up a small percentage of the hundreds of thousands of people using the drug worldwide.
Sharon Lewin, a professor at the University of Melbourne and director of the Doherty Institute, said that once the team at the Alfred hospital have determined if the man was using PrEP properly the HIV virus would be tested for signs of resistance.
"In cases of someone testing HIV positive while taking PrEP, we would first take a detailed history to understand how PrEP is being taken and potential exposures," Lewin told Fairfax Media on Tuesday.
"We would then look at the genetic code of the virus as this can tell us whether it is a drug-resistant strain, or a non-resistant strain. We would also look quite closely at drug levels in blood and the immune response to the virus, when the anti-body test became positive."
Around 10 percent of HIV virus strains diagnosed in Victoria have exhibited signs of a level of drug resistance.