An air steward notoriously blamed for starting the Aids epidemic in the US has been cleared of spreading the virus.

Gaetan Dugas, a French-Canadian gay man, was posthumously labelled "Patient Zero" by an unsympathetic media and accused of single-handedly being responsible for the spread of HIV and Aids across North America.

But a study in the journal Nature shows he was one of thousands of people infected by the virus years before HIV was recognised.

Before he died, Dugas assisted investigators with a significant amount of personal information as experts tried to establish whether Aids was caused by a sexually transmitted agent.

This, combined with confusion between a letter and a number, contributed to the invention of "Patient Zero" and the global defamation of Dugas, according to Cambridge University historian Dr Richard McKay.

Dr McKay said: "Gaetan Dugas is one of the most demonised patients in history, and one of a long line of individuals and groups vilified in the belief that they somehow fuelled epidemics with malicious intent."

Genetic analysis of HIV taken from a 1983 blood sample from Dugas showed he was not even a "base" case for strains of the virus prevalent at the time.

The study led by scientists at the University of Arizona confirmed HIV originally "jumped" from the Caribbean region to the US in around 1970, first emerging in New York City. From here, it quickly spread across the continent.