The effect of syndromic management interventions on the prevalence of sexually transmitted infections in South Africa
Introduction
Sexually transmitted infections (STIs) are a major contributor to the burden of disease in many developing countries [1]. Because of the difficulties associated with treating STIs in developing countries, the World Health Organization introduced syndromic management guidelines for the treatment of STIs and other reproductive tract infections in the early 1990s [2]. This strategy aims to treat all STI patients according to the symptoms with which they present, rather than deferring treatment until the results of laboratory tests are available. Apart from the obvious benefit to the patient of receiving immediate treatment, this strategy circumvents problems that may be experienced with limited laboratory facilities, coordination of patient receipt of test results, the high cost of laboratory tests and the limited sensitivity of certain tests [2], [3].
STI interventions such as this aim to eliminate infection at the individual level, as well as to reduce the prevalence of STIs at a population level [4]. However, most evaluations of syndromic management protocols for STI treatment have focused on their impact at the individual level [5], and only two community randomized controlled trials have assessed their impact at a population level [6], [7]. Several studies have documented declines in STI prevalence in African populations [8], [9], [10], [11], [12], [13], but it is difficult to determine the extent to which these reductions are attributable to improved STI treatment, as observed reductions in STI prevalence could also be attributable to changes in sexual behaviour [14] or AIDS mortality [15].
In the absence of strong evidence from controlled trials, the impact of syndromic management on STI prevalence at a population level can be evaluated using mathematical models, provided that these models are appropriately calibrated to local STI prevalence and treatment data, and provided that the models make appropriate allowance for other factors that may cause reductions in STI prevalence (i.e. behaviour change and AIDS mortality) [16], [17]. Such evaluations are particularly important in view of the growing scepticism regarding the benefits of syndromic management in HIV prevention [18], and can provide important insights into the reasons why syndromic management may fail to achieve significant reductions in STI prevalence at a population level.
This study aims to assess the likely effect of syndromic management protocols on STI prevalence levels in South Africa, a developing country with high levels of STI prevalence, which introduced syndromic management guidelines in its public health sector in 1994. Declines in the antenatal prevalence of syphilis have been observed over the last decade, and the South African Department of Health has attributed these to the success of the syndromic management programme [19]. However, there has been no formal evaluation of the extent to which improvements in STI treatment are responsible for the reduction in the prevalence of syphilis, and a lack of nationally representative data concerning the prevalence of other STIs has been an obstacle in assessing trends in the prevalence of these STIs [20]. This paper proposes a Bayesian modelling approach to evaluate the effect of syndromic management on the prevalence of STIs and other reproductive tract infections.
Section snippets
Methods
A mathematical model was developed to project the growth of the South African population over time, starting in 1985. The sexually active population is stratified by age, sex, marital status, propensity for concurrent partnerships, number of current partners, and risk group of partner(s). Individuals are assumed to move between these sexual activity states over time, and the rates at which they move between states are fixed at the mean values estimated in a previous analysis of South African
Results
As shown in previous publications [21], [28] and in Supporting information (Online appendix), the model produces estimates of HIV and STI prevalence that are reasonably consistent with South African survey results. Fig. 1 shows the posterior mean STI prevalence trends, for each of the four scenarios defined previously. Results are shown for women aged 15–49 (prevalence levels in men follow similar trends, although levels differ). Fig. 2 shows the percentage reductions in STI prevalence due to
Discussion
Previous reviews of the epidemiology of STIs in South Africa [20], [64] have noted that there is evidence of declining syphilis prevalence and declining proportions of genital ulcers attributable to chancroid, but that evidence of declines in the prevalence of other STIs is lacking. By fitting a mathematical model to the STI prevalence data, we have demonstrated that most of the observed reductions in syphilis and chancroid can be attributed to improvements in STI treatment and increases in
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