Sexually Transmitted Infections: Impact and Cost-Effectiveness of Prevention

Abstract

Sexually transmitted infections (STIs) impose major health and economic burdens globally. More than 35 bacterial, viral, and parasitic pathogens have been identified as sexually transmissible. An estimated 498.9 million new cases of four of the curable STIs occurred among adults ages 15–49 years in 2008, an increase of 11.3 percent from the estimated 448.3 million new cases in 2005 (WHO 2012a). In 2008, these cases included 105.7 million new cases of chlamydia, 106.1 million new cases of gonorrhea, 10.6 million new cases of syphilis, and 276.4 million new cases of trichomoniasis (WHO 2012a). Males accounted for 266.1 million (53 percent) new cases. At any point in 2008, an estimated 100.4 million adults were infected with chlamydia, 36.4 million with gonorrhea, 36.4 million with syphilis, and 187.0 million with trichomoniasis (WHO 2012a).The incidence and prevalence of these curable STIs varies remarkably across World Health Organization (WHO) regions, as shown in map 10.1, figure 10.1, and table 10.1. In general, low- and middle-income countries (LMICs) have higher estimated burdens of STIs than do high-income countries (HICs) (WHO 2012a). However, comparing income and STI burden by region can be challenging because income can vary substantially across countries within a given region. For example, the Americas include two relatively wealthy countries—Canada and the United States—yet the overall prevalence of these four curable STIs is higher in this than in any other region. The highest estimated prevalence and incidence rates of chlamydia and trichomoniasis occur in the Americas, while the highest rates of gonorrhea and syphilis are in Sub-Saharan Africa (figures 10.2 and 10.3) In general, trichomoniasis is the most prevalent STI across regions, with the exception of Europe and the Western Pacific, where chlamydia is more prevalent.A great deal of uncertainty surrounds the global and regional estimates of the incidence and prevalence of these four STIs (WHO 2012a). Relative to the size of the population in each region, the Americas has the highest annual incidence rate of these four curable STIs (0.264), followed by Africa (0.241), Western Pacific (0.130), Europe (0.104), Eastern Mediterranean (0.085), and South-East Asia (0.083). However, given heterogeneity in the quality of STI surveillance across regions, it is difficult to make cross-regional comparisons.The incidence of STIs can vary substantially within, as well as across, regions according to the WHO’s Global Health Observatory Data Repository. In 2010, the proportion of antenatal care attendees who were positive for syphilis was 0.2 percent in Cote d’Ivoire and 10.0 percent in the Central African Republic; the proportion of sex workers with active syphilis was 1.5 percent in Honduras and 17.5 percent in El Salvador; and the proportion with active syphilis among men who have sex with men (MSM) was 1.1 percent in Vietnam and 18.4 percent in Singapore. The incidence of STIs in a given country can vary substantially over time. For example, the percentage of MSM with active syphilis in Indonesia ranged from 4.0 percent in 2008 to 21.9 percent in 2012. Differences in the burden of STIs across regions, and within regions over time, preclude the identification of feasible programs and policies that can successfully reduce the burden of STIs in a cost-effective manner in all settings.