Bustling transport networks, migrant labor and changes to the sex trade in early 20th-century Congo created a "perfect storm" that gave rise to an HIV pandemic that has now infected 75 million people worldwide, researchers said on Thursday.

In an analysis of the genetic history of the human immunodeficiency virus (HIV) that causes AIDS, the scientists said the global pandemic almost certainly began its global spread in the 1920s in Kinshasa in Democratic Republic of Congo (DRC).

Here, a confluence of factors including urban growth, extensive railway links during Belgian colonial rule and changes in sexual behavior combined to see HIV emerge in Congo's capital and spread across the globe, Reuters reported.

Oliver Pybus, a professor at Oxford University's zoology department who co-led the research, said that until now most studies have taken a piecemeal approach to HIV's genetic history and looked only at certain HIV genomes in particular locations.

Pybus and an international team of researchers analyzed HIV-1 group M sequences from a major HIV sequence database and then combining these analyses with spatial and epidemiological data. Their study will be published in the journal "Science" on Thursday.