Is increasing gonorrhoea resistance in MSM is a result of more treatment, rather than greater sexual activity?

Emerging antibiotic resistance to the last-ditch treatment of Neisseria gonorrhoeae compels health policy-makers to balance opposing concerns.  On the one hand, successfully combating spread of the infection requires targeted treatment of core-group individuals.  On the other, a focus on the core-group causes a rebound in core-group incidence, with maximal dissemination of resistance (Chan & McCabe/STIs (C&M); Chan & Fisman/STIs).

Recent public health orthodoxy has tended to favour the more intensive screening of core-group individuals (Ison & Unemo (STI); Giguere & Alary/STIs; Lewis/STIs).  However Fingerhut & Althaus (F&A), in a recent modelling study, seek to shift the balance in the opposite direction.  They claim their model demonstrates that the wide disparity in the spread of resistance spread as between populations of MSM and of HMW (heterosexual men and women) reflects differing levels of treatment rather than differences in sexual behaviour (‘more sexual partners’).

So far as concerns the first part of the claim (‘gonorrhoea spreads faster with more treatment’), F&A’s findings corroborate those of C&M.  However, in coupling this with the claim that gonorrhoea spread is not the result of sexual behaviour (‘gonorrhoea (does not) spread faster with more sexual partners’) they place the balance of responsibility for spread with the prevailing policy of treatment.  This is presumably intended to push policy makers in the direction of a more conservative attitude to targeting testing and screening.

But can F&A really justify this  change of emphasis by differentiating the respective contributions of ‘more treatment’ as against ‘greater sexual activity’ to the difference in resistance between MSM and MSW popultions ?  We are wrong, the authors argue, to assume that ‘more partners’ amongst the MSM population necessarily entails more transmissions (p. 11) – and their model apparently demonstrates this.   A common sense response, however, would be to object that ‘more partners’ presumably implies ‘more sex acts with more partners’ – and that, even if ‘more partners’ does not in itself entail more transmissions, ‘more sex acts with more partners’ might certainly be expected to do so.

Interestingly, Althaus in another paper (see Althaus & Alizon) – admittedly, in connection with heterosexual groups – corroborates our common sense expectation by showing that the number of partners displays, if not a proportional, then at least a linear, relation  to number of sex acts. So can it really be the case that there is not a greater number of transmissions amongst the MSM population, given the greater number of partners? The authors evidently believe not.

Nevertheless, it would be interesting – as well as pertinent, I suspect, to the goals of the study – to have a more satisfying explanation of why, here, as elsewhere, common sense turns out to be wrong.