Sexually-transmitted infections (STIs), also known as sexually-transmitted diseases (STDs), are diseases that are commonly transmitted between partners through some form of sexual activity, most commonly vaginal intercourse, oral sex, or anal sex. They were commonly known as venereal diseases (VD) until some time around 1990, when public health officials introduced the new term in an effort to improve the clarity of their warnings to the public.
Note that all sexual behaviors that involve contact with another person or the bodily fluids of another person should be considered to contain some risk of transmission of sexually transmitted diseases. Most attention has focused on controlling HIV, which causes AIDS, but each STD presents a different situation.
As may be noted from the name, sexually transmitted diseases are transmitted from one person to another by certain sexual activities rather than being actually caused by those sexual activities. Bacteria, fungi, protozoa or viruses are still the causative agents. It is not possible to catch any sexually transmitted disease from a sexual activity with a person who is not carrying a disease; conversely a person who has an STD got it from contact (sexual or otherwise) with someone who had it, or their bodily fluids.
Although the likelihood of transmitting various diseases by various sexual activities varies a great deal, in general, all sexual activities between two (or more) people should be considered as being a two-way route for the transmission of STDs (i.e., "giving" or "receiving" are both risky). Regardless of one's status, solo masturbation is a safe activity.
Health care professionals suggest safer sex, such as the use of condoms in any sexual activity, but safer sex should by no means be considered an absolute safeguard. Abstinence from sexual activities involving other people will protect against sexual transmission of sexually-transmitted infections; however, it must be noted that STDs can also be transmitted through other activities involving transfer of and exposure to bodily fluids, such as blood transfusions and other blood products, sharing injection needles, needle-stick injuries (when medical staff are inadvertently jabbed or pricked with needles during medical procedures), sharing tattoo needles, and childbirth. These means of transmission make certain groups, such as doctors, haemophiliacs and drug users, particularly at risk.
Recent epidemiological studies have investigated the networks that are defined by sexual relationships between individuals, and discovered that the properties of sexual networks are crucial to the spread of sexually-transmitted diseases. In particular, assortative mixing between people with large numbers of sexual partners seems to be an important factor.
Since prostitutes tend to have large numbers of sexual partners, prostitution without the use of safer sex precautions has often been associated with the spread of sexually transmitted diseases. Some travellers such as truck drivers and sailors also often have high numbers of sexual partners (often prostitutes). However, sexually transmitted diseases are potentially transmitted in any form of sexual relationship, so it is important that all members of the community who are engaged in sexual relationships use safer sex precautions, regardless of the nature of their relationships.
It is possible to be an asymptomatic carrier of sexually transmitted diseases. In particular, sexually transmitted diseases in women often cause the serious condition of pelvic inflammatory disease.
Sexually-transmitted diseases have been well-known for hundreds of years — the English language has short words for two of the most common: the "pox" (syphilis) and "the clap" (gonorrhea).
Prior to the invention of modern medicines, sexually-transmitted diseases were generally incurable, and treatment was limited to treating the symptoms of the disease. The first venereal diseases clinic opened on January 31, 1747 at London Dock Hospital.
The first effective treatment for a sexually-transmitted disease was salvarsan, a treatment for syphilis. With the discovery of antibiotics, a large number of sexually-transmitted diseases became easily curable, and this, combined with effective public health campaigns against STIs, led to a public perception during the 1960s and 1970s that they had ceased to be a serious medical threat.
During this period, the importance of contact tracing in treating STIs was recognized. By tracing the sexual partners of infected individuals, testing them for infection, treating the infected and tracing their contacts in turn, STI clinics could be very effective at suppressing infections in the general population.
In the 1980s, first genital herpes and then AIDS emerged into the public consciousness as sexually transmitted diseases that could not be cured by modern medicine. AIDS in particular has an asymptomatic period which allowed the disease to be spread to others, followed by a symptomatic period which leads rapidly to death unless treated. Recognition that AIDS threatened a global pandemic led to public information campaigns and the development of treatments that allow AIDS to be managed by suppressing the HIV virus for as long as possible. Contact tracing continues to be an important measure, even when diseases are incurable, as it helps to contain infection.
There is now a recognition that safer sex is the most reliable way of protecting against all sexually-transmitted diseases, both curable and incurable.
Types and their causative organisms
Note: All of the diseases on this list can be transmitted sexually. Some of the diseases on this list are commonly transmitted in other ways besides sexually, for example, AIDS is also commonly transmitted through the sharing of infected needles by drug users, and candidiasis, whilst it can be sexually transmitted, is very often not associated with sexual activity.