Tracing the global spread of AIDS

"Patient Zero"

Gaetan Dugas, a Canadian flight attendant, was initially believed to be Patient Zero for the American AIDS epidemic.

The legend of Patient Zero began with a 1984 study that traced the sexual contacts of 40 men with Kaposi's sarcoma - a type of cancer - or other indicators of late-stage AIDS. Eight of them were found to have had sex with the same person – Dugas.

Dugas was designated Patient O (for "outside Southern California", where the study began). However, the ambiguous circular symbol on a chart was later read as a zero.

His name was not cleared until 2016, when researchers concluded in a paper published on the journal Nature that he was not the source of the virus in the US.

Researchers said the 1984 study incorrectly assumed most patients developed AIDS symptoms within 10 months of infection. In reality, it takes years – so many participants may have been infected long before meeting Dugas.