The year 1939 saw total US syphilis deaths at 15 per 100,000 and syphilis deaths of black males at 72.5 per 100,000: this is a death rate comparable to that for HIV/AIDS at the height of the epidemic in 1995 when total deaths and deaths of black males stood, respectively, at 16.2 and 80.2 per 100,000.  Subsequently, in the late 40s and early 50s, incidence and mortality from syphilis were to fall precipitously – thanks to penicillin.  A recent paper in the Archives for Sexual Behavior by an economist, Andrew Francis, argues for the importance of this collapse in the “cost” of syphilis in spurring the sexual revolution (http://link.springer.com/article/10.1007%2Fs10508-012-0018-4). His exploration of this hypothesis prompts general reflection on the link between the “cost” of disease (which he equates with absence of an effective treatment) and sexual behaviour.

The paper correlates data across US states on syphilis incidence and mortality with measures of “risky non-traditional sex” – which, in the context of the poverty of relevant data for the period, is evaluated on the basis of gonorrhoea rate, illegitimate birth ratio and teen birth share.  Coefficients are given from regressions of measures of sexual behaviour on indicators for the number of years since syphilis collapse (which varies by state).  As regards illegitimate birth ratio and teen birth share, a positive correlation emerges which goes back as early as three years or less from syphilis collapse; gonorrhoea, however, continues to decline from its WW2 peak, as we might expect.

Ultimately, however, Francis’s argument rests also on the claim that his own explanation of sexual revolution fits the facts better than the alternative explanations, of which the most familiar is that “anti-conception technology”, especially the pill, played a decisive role.  Francis admits that, from the late sixties, conception technologies and measures of risky behaviour increase simultaneously.  Yet measures of risky sexual behaviour, he claims, had already been rising sharply for a decade before anti-conception technology began to make its impact.  His own data show that the two changes do not coincide.   Nor do measures of permissive values or religious observance show any discontinuous change that would coincide with the increase in risky behaviour.  So if Francis’ hypothesis is wrong, then the precise timing of the sexually revolution remains mysterious.  Francis gestures vaguely towards the possibility of the change in sexual behaviour being triggered by still less definable “economic, social and cultural changes”.

The obvious recent parallel to the syphilis collapse in our own times would be impact of the introduction of HAART on HIV/AIDS mortality.  The concern that an effective therapy might lead to disinhibition has been widely discussed in STI journal and elsewhere.  An increase in risk-taking behaviour among MSM during the late 1990s has been established:  http://sti.bmj.com/content/77/3/184.abstract?sid=5d909365-4627-4232-8ef4-a93445f5baed (Stolte & Coutinho: Amsterdam);  http://sti.bmj.com/content/80/6/451.abstract?sid=5d909365-4627-4232-8ef4-a93445f5baed (Elford & Hart: London); http://sti.bmj.com/content/80/6/518.abstract?sid=5d909365-4627-4232-8ef4-a93445f5baed(Cox & Allard: Montreal); http://sti.bmj.com/content/79/1/7.abstract?sid=5d909365-4627-4232-8ef4-a93445f5baed (Stephensen & Williams: London).  But opinions on the contribution of HAART to changing sexual behaviour seem divided, with Stolte & Coutinho supporting the hypothesis, and the others inclined to attribute it to other factors.  The probable future emergence of multi-resistant gonorrhoea (http://sti.bmj.com/content/87/Suppl_2/ii39) represents the inverse case (loss of a therapy leading to potential inhibition).  If the diminished “cost” of an STI (syphilis) can spur an increase in risky sexual behaviour, should we not expect an increased cost to have the opposite result?  Time will tell.