The next two columns (G and H) contrast condom use in Thai men visiting sex workers, which was as near to 100 per cent as any use of condoms is likely to get, and the proportion of teenage boys in one province who used condoms during sex with girlfriends.

As cited already, the “100 per cent condom campaign” in 1990-92 in Thailand is often seen as one of the most successful HIV prevention programmes of all time. It slashed HIV incidence among young men from 2.5 per cent a year to 0.5 per cent, reduced prevalence among army recruits from 10 per cent to 2.5 per cent, and it is estimated that HIV prevalence in Thailand today is still – a decade after the campaign ended - 50 per cent lower than it would have been if it had not happened.

Its success was partly due to good timing and an accurate perception that a widespread culture of commercial sex was responsible for the rapid growth of HIV at the time. It was also partly due to it being an easily enforceable target. The campaign put pressure on brothel owners to enforce 100 per cent condom use in their establishments and ensured that ones not conforming to this rule were closed by the police.

Since then, however, the continued impact of tourism and the global media, and the growing affluence of Thailand, has led to a change in sexual behaviour. A pattern whereby men would marry young but also have extramarital commercial sex has given way to a more ‘westernised’ pattern of teenagers having pre-marital sexual relationships. The report that only 25 per cent of Thai teenagers were using condoms led to a campaign to have condom machines placed in colleges and a counter-campaign resisting this – with both demands coming from students themselves. As sexual and drug-using cultures change, HIV prevention has to fight the same battle many times again on behalf of new populations.