What are sexually transmitted infections? Sexually transmitted infections (STIs) are infections whose primary route of transmission is through sexual contact. STIs can be caused by mainly bacteria, viruses, or protozoa. In the developed world, viral diseases have become increasingly common and important, whereas bacterial STIs are more common in developing countries, but even this is changing with the increasing recognition of viral diseases. The three most common presenting symptoms of an STI are urethral discharge, genital ulceration, and vaginal discharge with or without vulval irritation. The three most common STIs seen in clinics in the United Kingdom are genital warts, chlamydial infections, and gonococcal infections. Trichomoniasis, pediculosis pubis, and genital herpes are common and are sexually transmitted. Scabies and vaginal candidiasis often are diagnosed in STI clinics, although they are not usually acquired sexually. Finally, sexually transmitted hepatitis (A, B, and C) and HIV are becoming more common. The consequences Sexually transmitted infections are a major public health problem and are one of the most common causes of illness, and even death, in the world today. They have far reaching health, social, and economic consequences, particularly in the developing world. The World Bank estimated that for women aged 15-44 years, STIs (excluding HIV) were the second most common cause of healthy life lost after maternal morbidity. Other studies have estimated that 5% of the total discounted healthy life years lost in sub-Saharan Africa are caused by STIs, excluding HIV, and that HIV alone accounts for 10% of healthy life years lost. Complications and cost Most STIs are easy to diagnose and cheap to treat; however, viral conditions, such as herpes and HIV, are costly and incurable. Many infections remain unrecognised and undiagnosed, which results in considerable long term morbidity, which can be costly in human and monetary terms.
The complications of untreated infections are far reaching, and include cancer, reproductive problems, and pregnancy related problems. Reproductive ill health (death and disability related to pregnancy and childbirth, STIs, HIV, AIDS, and reproductive cancers) has been calculated to account for 5-15% of the global burden of disease. Data on the monetary costs of the complications of STIs are sparse, particularly for the developing world. American data give estimates of total direct and indirect costs attributable to STIs to be $9.9 m annually, rising to $16.6 m if HIV and AIDS are included. In the United Kingdom only limited data are available. For example, the prevention of unplanned pregnancy by NHS contraception services probably saves over £2.5 billion per year, and the average lifetime treatment cost for an HIV positive person is between £135 000 and £180 000, with a monetary value of preventing a single onward transmission of somewhere between £0.5 m to £1 m in terms of individual health benefits and treatment costs. Finally, but not calculated accurately, dramatic cost savings can be made by preventing infertility. Few economic data exist in the developing world in relation to the consequences of STIs, which are considerable and personally devastating. Many women become infertile without even realising that they have suffered from pelvic inflammatory disease. Estimates of the burden of infections for women in urban Africa have shown that chlamydial infection causes an average of 4.8 lost days of productive life and syphilis leads to 8.2 days per capita per year. Estimates suggest that with the high prevalence of syphilis in pregnant women, for example 10%, up to 8% of all pregnancies (beyond 12 weeks) would have an adverse outcome.