Younger men were also more promiscuous, with 35% in 1998 saying they had had two or more sexual partners in the previous 12 months, compared with 25% of women aged between 16 and 24.

BBC: Depressed man

Male circumcision helps prevent infection, and women are vulnerable to rape and also tend to have sexual partners who are older, and therefore more likely to have picked the virus up at some point during their lives.

ECONOMIST: Building better models of the prevalence of HIV

He was a frequent visitor to the Sandstone Ranch - a kind of retreat for sexual adventure, where clothes were more often off than on, and sex with multiple partners was the norm.

BBC: How the Joy of Sex was illustrated