Heterosexual HIV transmission and STD prevalence - predictions of a theoretical model

Heterosexual HIV transmission and STD prevalence - predictions of a theoretical model

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Original article Heterosexual HIV transmission and STD prevalence: predictions of a theoretical model Adrian M Renton, Luke Whitaker, Mark Riddlesdell Background: Previous studies suggest that concurrent sexually transmitted infection may enhance HIV transmission. This paper explores some theoretical consequences of this using a mathematical model of transmission of HIV and other STD pathogens. Objectives: To develop a deterministic mathematical model to describe the heterosexual trans- mission dynamics of both HIV and a bacterial STD. Study design: We used survey derived estimates of sexual behaviour in a young heterosexual London population in our deterministic mathematical model to estimate the e V ects on an HIV epidemic of di V erent levels of STD prevalence in such a population. Results: We show that the predictions of the model are plausible and suggest that, even under conditions both of low STD prevalence and of low HIV transmission enhancement, a substantial proportion of HIV transmission events may be attributable to concurrent STD. Conclusions: It is likely that epidemics of heterosexually transmitted HIV infection in industr- ialised countries have been limited in size by the relative success of e V orts to control STD. None the less, a significant proportion of heterosexual transmission events which do occur may be attributable to concurrent STD. In developing countries, cheap and simple STD care is likely to be a highly cost e V ective strategy to prevent HIV transmission. ( Sex Transm Inf 1998; 74 :339–344) Keywords: HIV transmission; STD prevalence; model Introduction Marked di V erences in the size of the epidemics of human immunodeficiency virus (HIV) infection in di V erent parts of the world are well recognised but poorly understood. In particu- lar, HIV prevalence among heterosexuals has increased more rapidly, and reached higher levels in many developing countries compared with industrialised countries. During the 1980s explanations for this were generally couched in terms of di V erences either in patterns of sexual behaviour or in the potential for medically related transmission. In 1988 it was proposed that the higher HIV prevalence found in some developing countries might be explained by the concomitantly higher prevalence of sexually transmitted diseases (STD), if the presence of STD in an HIV exposed or infected individual enhanced the transmission of HIV. 1 There are several mechanisms through which such en- hancement might be e V ected. An STD which leads to ulceration of the genital skin or mucosa might facilitate ingress or egress of HIV carrying body fluids. 1–3 Some of the inflamma- tory cells which infiltrate and shed from genital mucosa in the presence of various STDs are known to be primary targets for HIV infection, 45 and the presence of inflammatory cells in the male and female genital tract has been shown to be correlated with the presence and quantity of HIV detectable in sperm, 67 and cervicovaginal secretions.
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Heterosexual HIV transmission and STD prevalence - predictions of a theoretical model

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