Many gay men at the time resisted the idea that unprotected sex spread HIV, says the dermatologist. “It was a very difficult thing — because they had fought so much for sexual freedom and for recognition and acceptance — to be told that every gay man is potentially a carrier of this terrible disease.”

The study is a lesson in how scientifically and ethically difficult it can be to identify a 'patient zero', says McKay. Dugas’ story emphasizes that HIV was “not just a retrovirus undergoing change in some timeless void”, he adds. The quest for scientific understanding of the disease had a very real impact on the man and his family.