New HIV cases attributable to syphilis in the USA: estimates from a simplified transmission model

Objective: Because syphilis can raise the likelihood of HIV transmission an d acquisition, syphilis prevention in the USA has the potential benefit of reducing the number of new cases of HIV. We developed a simplified transmis sion model to estimate the annual number and cost of new, heterosexually-ac quired HIV cases in the USA attributable to syphilis. Design: We estimated the number of heterosexual, HIV serodiscordant partner ships in which syphilis was present in 1996. The model included the probabi lity of transmission of HIV (with and without the presence of syphilis) and other parameters based on data from recent literature. Published direct co sts (HIV treatment costs including antiretroviral therapy) and indirect cos ts (e.g., lost productivity) per case of HIV were used to estimate the annu al cost of HIV cases attributable to syphilis. The potential savings in ave rted HIV costs related to syphilis were used to estimate the potential bene fits of a syphilis elimination program. Results: In 1996, an estimated 1082 new heterosexual cases of HIV in the US A could be attributed to syphilis. These cases represented direct costs of US$ 211 million and indirect costs of US$ 541 million; yielding US$ 752 mil lion in total costs. Over 15 years, a syphilis elimination program could sa ve over US$ 833 million (discounted at 3% annually) in averted direct medic al costs of syphilis-related HIV infections. Conclusions: If the only benefit of syphilis elimination were to prevent ne w HIV cases attributable to syphilis, a national syphilis elimination progr am costing less than US$ 833 million would probably pay for itself. (C) 199 9 Lippincott Williams & Wilkins.