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Mother-to-child syphilis transmission

What can cost-effectiveness modelling tell us about the feasibility of eliminating congenital syphilis in sub-Saharan Africa?

20 Nov, 13 | by Leslie Goode, Blogmaster

The WHO global initiative for the elimination of congenital syphilis (2007) set the goal of expanding antenatal testing to >90% by 2015.  In sub-Saharan Africa (SSA) recent estimates place the number of mothers infected with active syphilis at 535,000 p.a..  Adverse outcomes – stillbirths, neo-natal morbidity and congenital disease – affect 53%-82% of these pregnancies, as compared with 10%-21% of women without syphilis.  Yet, perhaps surprisingly,  74% of pregnant women in SSA are reported to attend an antenatal clinic at least once.  Administration at the routine visit of a simple point-of-care test (POCT), plus, in the case of detection, an intra-muscular injection of benthazine penicillin, is all that, in most cases, would be required to deal with the problem.

A recent modelling study (Kuznik & Manabe ) seeks to make the economic case for universal POCT syphilis screening in 43 countries in SSA.  It estimates the cost of increasing syphilis testing at antenatal clinics from whatever it is at present to 100% through universal adoption of the immunochromatographic strip test (ICT), and the benefits that would result in terms of saved lives and reduced morbidity.  It then calculates the cost-benefit in US dollars per Disability Adjusted Life Year (DALY).

The findings are given for each of the 43 countries considered. Here are the aggregate findings for SSA as a whole.  In order to ensure screening coverage for the 23.5 million (74%) pregnant mothers attending ante-natal clinics, the cost is estimated at a comparatively modest US$20.8 million per year, and would, it is claimed, reduce incidence of still-birth, neo-natal death and congenital syphilis by 64,000, 25,000 and 32,000, respectively.  Of the 43 countries in the model the cost of such an intervention per DALY averted would be less than US$20 in 37 cases, and less than US$10 in 23 cases.

The study claims to be the first to have evaluated the cost-effectiveness of ICT across SSA.  What is the value of this exercise?  It seems to consist primarily in the extra rhetorical “punch” it can lend to the argument in favour of doing something – and something very cheap – in order to alleviate the deplorable ravages of perinatal mortality and morbidity due to syphilis.  One can only applaud the intentions of its authors.  At the same time, one is struck by the inadequacy of the measure employed (cost per DALY ) to capture any real sense of the economic (let alone human) cost of MCST.  The impressive figures they arrive at for cost-effectiveness of the proposed interventions owes not a little to the fact that the lost life-years averted happen to be those of the stillborn or neonatal deceased.  This does not belittle the cost, but feels a rather odd way of looking at perinatal outcomes.  Consequently the whole exercise, while it may be well-intentioned and ticks all the official boxes, strikes this reader at least as rather specious.  One wonders if it can offer any real ground for the prioritization of MCST as against other equally laudable interventions: if it does, one feels somehow that it ought not to!

Relevant to the real economic cost confronting any country deciding to switch to the ICT would presumably be the relative cost of the ICT compared to an established alternative (e.g. Rapid Plasma Reagin (RPR)).  After all, using ICT to make up the shortfall in current testing levels presupposes the country has made the switch from RPR to ICT – which may already have cost implications (Vickerman and Watts).  Ultimately, however, the main the challenge of making this switch, may not be economic cost at all, but a problem of institutional organization and training (STI blog/Peeling & Mabey).   Peeling & Mabey observe in relation to one area in which POCT for syphilis was being introduced as part of a trial “a 65% drop over the first six months in the percentage of antenatal clinics passing the quality assurance controls due to high staff turn-over: but, subsequently, with the HWC training mechanism kicking in, there was a return to 100% levels of proficiency”.  Here and elsewhere (Peeling & Mabey) make the case for the importance of “programme science” to “address the gap” between test performance and successful deployment.

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