Canadian flight attendant Gaetan Dugas was framed as Patient Zero for AIDS. Credit:Commons The new analysis shows that Dugas' own blood, sampled in 1983, contained a viral strain already infecting men in New York before he began visiting gay bars here after being hired by Air Canada in 1974. The researchers also reported that originally Dugas was not even called Patient Zero - in an early epidemiological study of cases, he was designated Patient O, for "outside Southern California" where the study began. The ambiguous circular symbol on a chart was later read as a zero, stoking the notion that blame for the epidemic could be placed on one man. Myths like that of Patient Zero echo in prevention efforts even today, experts said. Many vulnerable groups, including young gay men and African women, fail to use protective drugs or avoid testing because they fear being stigmatised or accused of being carriers. Reflecting on the epidemic's early days, Anthony Fauci, then a doctor treating AIDS patients and now the director of the National Institute of Allergy and Infectious Diseases, said he remembered it seeming plausible at the time that one person was responsible.

A mannequin wears headgear made of red condoms at the 2016 International AIDS Conference in Durban, South Africa. Credit:AP In hindsight, he added, the idea now seems absurd. "We were unaware of how widespread it was in Africa," Dr Fauci said. "Also, we thought, based on very little data, that it was only about two years from infection to death." The new data are consistent with the scenario described in 2011 in The Origins of AIDS, by Jacques Pepin, an infectious disease specialist at the University of Sherbrooke in Quebec. A Ugandan model on the runway at the third annual Uganda Network of Young People Living with HIV pageant last month. The event aims at encouraging youth to open up and educate others. Credit:AP Relying on previous genetic research and African colonial records, Dr Pepin showed that HIV was carried from Kinshasa to Haiti in the 1960s - most likely by one of the thousands of Haitian civil servants recruited by the United Nations to work in the former Belgian Congo after colonial rule collapsed.

In Haiti, he theorised, a few cases were multiplied by unsterile conditions at a private blood-collecting company, Hemo-Caribbean, that opened in 1971 and exported more than 6000 litres of plasma to the United States monthly. Plasma clotting factors were used by US haemophiliacs, many of whom died of AIDS. Haiti also was a sex-tourism destination for gay men, another route the virus could have taken to New York. It is now estimated that 5.1 million people in India are HIV positive. Credit:Jessica Shapiro The blood samples analysed in the new study were collected in 1978 and 1979 in New York and San Francisco as part of an effort to make a hepatitis B vaccine. Researchers stored almost 16,000 blood samples; nearly 7 per cent of those from New York and 4 per cent of those from California later turned out to be infected with HIV. A team led by Michael Worobey, an evolutionary biologist at the University of Arizona in Tucson and lead author of the Nature paper, sequenced the genomes of the HIV found in some of those samples and compared them with viral DNA in samples collected in the early 1980s from Haitians, Dominicans and others treated in US hospitals. Because decades spent in freezers had degraded many samples, Dr Worobey said, his lab developed an "RNA jackhammering" technique similar to that used to reconstruct the ancient Neanderthal genome. Counting mutations allowed the researchers to "wind back the molecular clock" and see when each strain of HIV diverged from its ancestors.

Africa has a dozen HIV groups, and Haiti's epidemic came from one of those. The New York samples all derive from one Haitian strain, and those from San Francisco are all so closely related that they probably all resulted from one person introducing one New York strain, Dr Worobey said. The symptoms that later were called AIDS were first recognised in 1981, and the legend of Patient Zero began with a 1984 study that traced the sexual contacts of 40 gay men with Kaposi's sarcoma or other indicators of late-stage AIDS. Eight of them, half in New York and half in Southern California, had sex with an unnamed flight attendant. Initially described as "Case 057" and then as Patient O, he reported having about 250 sexual partners a year. The legend itself sprang from the publicity campaign for a best-selling 1987 book And the Band Played On by Randy Shilts, a gay San Francisco journalist who himself died of AIDS in 1994. In a 1993 interview, Shilts said he had heard CDC investigators use the term Patient Zero and thought "Oooh, that's catchy."

By hunting down ex-boyfriends of men in the 1984 study, Shilts established that the flight attendant was Dugas, who was born in Quebec but lived his last years in Vancouver.