Epidemiology of sexually transmitted infections

Although accurate incidence figures are not available in most countries, sexually transmitted infections (STIs) (excluding HIV) are estimated to cause more than 5% of the global burden of disease. The burden falls especially heavily on women and infants, with more than half a million perinatal deaths attributable to syphilis annually. Mobile populations, those with many sexual partners, and those whose partners have many partners are at increased risk, and the prevalence of treatable STIs is many times higher in poor populations, who often lack access to effective treatment. Other STIs, especially those that cause genital ulceration, increase the risk of HIV transmission.

Incidence

In Western countries, the reported incidence of many STIs fell during the 1980s and 1990s, probably as a result of changes in sexual behaviour resulting from the HIV epidemic, but has increased subsequently. The reported incidence of Chlamydia trachomatis infection has increased in the general population, especially in teenagers and young adults, and the incidence of syphilis has increased in core groups, including homosexual men.

Strategies to control STIs

These include health education and the promotion of condoms; the provision of accessible, acceptable, and affordable clinical services to provide effective treatment and hence prevent complications and further transmission; and partner notification to reach infected people who may not present to a health facility. Since many STIs are asymptomatic, screening programmes may also play an important role. Screening of pregnant women for syphilis is recommended policy in most countries, and has been shown to be cost-effective even where the prevalence is low. Screening programmes for C. trachomatis infection have recently been implemented in some Western countries, but their impact is uncertain.