From Simon King-Spooner
Routine HIV testing would indeed help prevent the transmission of the virus (22 July, p 8). You make the point – as I did some years ago in New Scientist – that those who know they are infected tend to do more to avoid passing on the virus than those who think they aren’t do to avoid catching it (21 March 1998, p 50).
It should also be recognised that cultivating such “preventive altruism”, with interventions aimed at infected individuals rather than at the wider uninfected population, would be likely to have a disproportionately greater effect in stemming the spread of HIV. This is because HIV-negative people just about always outnumber HIV-positive people, usually many times over, and the impact of any particular individual taking up a preventive measure would reflect that disproportion. If, for example, the prevalence of the virus is 1 per cent, 99 negative folk would need to be persuaded to take up condom use to have the preventive impact of persuading a single positive person to do the same – a task which would generally be easier anyway, given the tendency to preventive altruism.
An important opportunity has been missed through the overwhelming emphasis of HIV prevention work on uninfected populations. Routine testing would make it easier to start redressing that imbalance.
Linlithgow, West Lothian, UK
