When Elizabeth Pisani began her career as an HIV epidemiologist, fewer than 1.5m cases of Aids had been reported across the world. Within a year, by the end of 1997, 30 million people were estimated to be infected with HIV. As Pisani wrote in her first report for World Aids Day, that meant one in every 100 sexually active adults aged between 15 and 49 worldwide.

Today, just over a decade later, the global figure is estimated to be closer to 40 million, with more than 1.5m new infections every year. Yet there is a widespread impression that the world is now winning the fight against the virus. The perception that it threatens only sex workers, heroin addicts and gay men has been replaced by the urgent consensus that this is a universal problem - backed by mind-boggling sums.

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