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Sexually Transmitted Infections
Classification and external resources
Spanish Civil War poster, produced by the Republican government, saying "Avoid venereal diseases ... As dangerous as enemy bullets"
ICD-10	A64.
ICD-9	099.9
DiseasesDB	27130
MeSH	D012749

A sexually transmitted disease (STD), also known as sexually transmitted infection (STI) or venereal disease (VD), is an illness that has a significant probability of transmission between humans or animals by means of human sexual behavior, including vaginal intercourse, oral sex, and anal sex. While in the past, these illnesses have mostly been referred to as STDs or VD, in recent years the term sexually transmitted infection (STI) has been preferred, as it has a broader range of meaning; a person may be infected, and may potentially infect others, without showing signs of disease. Some STIs can also be transmitted via the use of IV drug needles after its use by an infected person, as well as through childbirth or breastfeeding. Sexually transmitted infections have been well known for hundreds of years.

Classification and terminology

Until the 1990s, STDs were commonly known as venereal diseases : Veneris is the Latin genitive form of the name Venus, the Roman goddess of love. Social disease was another euphemism.

Public health officials originally introduced the term sexually transmitted infection, which clinicians are increasingly using alongside the term sexually transmitted disease in order to distinguish it from the former. According to the Ethiopian Aids Resource Center FAQ, "Sometimes the terms STI and STD are used interchangeably. This can be confusing and not always accurate, so it helps first to understand the difference between infection and disease. Infection simply means that a germ—virus, bacteria, or parasite—that can cause disease or sickness is present inside a person’s body. An infected person does not necessarily have any symptoms or signs that the virus or bacteria is actually hurting his or her body; they do not necessarily feel sick. A disease means that the infection is actually causing the infected person to feel sick, or to notice something is wrong. For this reason, the term STI—which refers to infection with any germ that can cause an STD, even if the infected person has no symptoms—is a much broader term than STD."^[1] The distinction being made, however, is closer to that between a colonization and an infection, rather than between an infection and a disease.

Specifically, the term STD refers only to infections that are causing symptoms. Because most of the time people do not know that they are infected with an STD until they start showing symptoms of disease, most people use the term STD, even though the term STI is also appropriate in many cases.

Moreover, the term sexually transmissible disease is sometimes used since it is less restrictive in consideration of other factors or means of transmission. For instance, meningitis is transmissible by means of sexual contact but is not labeled as an STI because sexual contact is not the primary vector for the pathogens that cause meningitis. This discrepancy is addressed by the probability of infection by means other than sexual contact. In general, an STI is an infection that has a negligible probability of transmission by means other than sexual contact, but has a realistic means of transmission by sexual contact (more sophisticated means—blood transfusion, sharing of hypodermic needles—are not taken into account). Thus, one may presume that, if a person is infected with an STI, e.g., chlamydia, gonorrhea, genital herpes, it was transmitted to him/her by means of sexual contact.

The diseases on this list are most commonly transmitted solely by sexual activity. Many infectious diseases, including the common cold, influenza, pneumonia, and most others that are transmitted person-to-person can also be transmitted during sexual contact, if one person is infected, due to the close contact involved. However, even though these diseases may be transmitted during sex, they are not considered STDs.

Bacterial

• Chancroid (Haemophilus ducreyi)
• Chlamydia (Chlamydia trachomatis)
• Granuloma inguinale or (Klebsiella granulomatis)
• Gonorrhea (Neisseria gonorrhoeae)
• Syphilis (Treponema pallidum)

Fungal

• Tinea cruris "Jock Itch" (Trichophyton rubrum and others)—Sexually transmissible
• Candidiasis or "yeast Infection"

Viral

Micrograph showing the viral cytopathic effect of herpes (ground glass nuclear inclusions, multi-nucleation). Pap test. Pap stain.

• Viral hepatitis (Hepatitis B virus)—saliva, venereal fluids.
  (Note: Hepatitis A and Hepatitis E are transmitted via the fecal-oral route; Hepatitis C (liver cancer) is rarely sexually transmittable,^[2] and the route of transmission of Hepatitis D (only if infected with B) is uncertain, but may include sexual transmission.^[3][4][5])
• Herpes simplex (Herpes simplex virus 1, 2) skin and mucosal, transmissible with or without visible blisters
• HIV/ AIDS (Human Immunodeficiency Virus)— venereal fluids
• HPV (Human Papilloma Virus)— skin and mucosal contact. 'High risk' types of HPV are known to cause most types of cervical cancer, as well as anal, penile, and vulvar cancer, and genital warts.
• Molluscum contagiosum (molluscum contagiosum virus MCV)—close contact

Parasites

• Crab louse, colloquially known as "crabs" (Phthirius pubis)
• Scabies (Sarcoptes scabiei)

Protozoal

• Trichomoniasis (Trichomonas vaginalis)

Sexually transmitted enteric infections

Various bacterial (Shigella, Campylobacter, or Salmonella), viral (Hepatitis A, Adenoviruses), or parasitic (Giardia or amoeba) pathogens are transmitted by sexual practices that promote anal-oral contamination (fecal-oral). Sharing sex toys without washing or multiple partnered barebacking can promote anal-anal contamination. Although the bacterial pathogens may coexist with or cause proctitis, they usually produce symptoms (diarrhea, fever, bloating, nausea, and abdominal pain) suggesting disease more proximal in the GI tract.

Pathophysiology

Many STDs are (more easily) transmitted through the mucous membranes of the penis, vulva, rectum, urinary tract and (less often—depending on type of infection)^{[citation needed]} the mouth, throat, respiratory tract and eyes. The visible membrane covering the head of the penis is a mucous membrane, though it produces no mucus (similar to the lips of the mouth). Mucous membranes differ from skin in that they allow certain pathogens into the body.^[6] Pathogens are also able to pass through breaks or abrasions of the skin, even minute ones. The shaft of the penis is particularly susceptible due to the friction caused during penetrative sex. The primary sources of infection in ascending order are venereal fluids, saliva, mucosal or skin (particularly the penis), infections may also be transmitted from feces, urine and sweat.^[7] The amount required to cause infection varies with each pathogen but is always less than you can see with the naked eye.

This is one reason that the probability of transmitting many infections is far higher from sex than by more casual means of transmission, such as non-sexual contact—touching, hugging, shaking hands—but it is not the only reason. Although mucous membranes exist in the mouth as in the genitals, many STIs seem to be easier to transmit through oral sex than through deep kissing. According to a safe sex chart, many infections that are easily transmitted from the mouth to the genitals or from the genitals to the mouth, are much harder to transmit from one mouth to another.^[8] With HIV, genital fluids happen to contain much more of the pathogen than saliva. Some infections labeled as STIs can be transmitted by direct skin contact. Herpes simplex and HPV are both examples. KSHV, on the other hand, may be transmitted by deep-kissing but also when saliva is used as a sexual lubricant.

Depending on the STD, a person may still be able to spread the infection if no signs of disease are present. For example, a person is much more likely to spread herpes infection when blisters are present (STD) than when they are absent (STI). However, a person can spread HIV infection (STI) at any time, even if he/she has not developed symptoms of AIDS (STD).

All sexual behaviors that involve contact with 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 his/her bodily fluids. Some STDs such as HIV can be transmitted from mother to child either during pregnancy or breastfeeding.

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 although receiving carries a higher risk.

Healthcare professionals suggest safer sex, such as the use of condoms, as the most reliable way of decreasing the risk of contracting sexually transmitted diseases during sexual activity, but safer sex should by no means be considered an absolute safeguard. The 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 are other avenues of transmission. These different means put certain groups, such as medical workers, and 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.

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.

Prevention

Prevention is key in addressing incurable STIs, such as HIV & herpes.

The most effective way to prevent sexual transmission of STIs is to avoid contact of body parts or fluids which can lead to transfer with an infected partner. No contact minimizes risk. Not all sexual activities involve contact: cybersex, phonesex or masturbation from a distance are methods of avoiding contact. Proper use of condoms reduces contact and risk.

Ideally, both partners should get tested for STIs before initiating sexual contact, or before resuming contact if a partner engaged in contact with someone else. Many infections are not detectable immediately after exposure, so enough time must be allowed between possible exposures and testing for the tests to be accurate. Certain STIs, particularly certain persistent viruses like HPV, may be impossible to detect with current medical procedures.

Many diseases that establish permanent infections can so occupy the immune system that other diseases become more easily transmitted. The innate immune system led by defensins against HIV can prevent transmission of HIV when viral counts are very low, but if busy with other viruses or overwhelmed, HIV can establish itself. Certain viral STI's also greatly increase the risk of death for HIV infected patients.

Vaccines

Vaccines are available that protect against some viral STIs, such as Hepatitis B and some types of HPV. Vaccination before initiation of sexual contact is advised to assure maximal protection.

Condoms

Condoms only provide protection when used properly as a barrier, and only to and from the area that it covers. Uncovered areas are still susceptible to many STDs. In the case of HIV, sexual transmission routes almost always involve the penis, as HIV cannot spread through unbroken skin, thus properly shielding the insertive penis with a properly worn condom from the vagina and anus effectively stops HIV transmission. An infected fluid to broken skin borne direct transmission of HIV would not be considered "sexually transmitted", but can still theoretically occur during sexual contact, this can be avoided simply by not engaging in sexual contact when having open bleeding wounds. Other STDs, even viral infections, can be prevented with the use of latex condoms as a barrier. Some microorganisms and viruses are small enough to pass through the pores in natural skin condoms, but are still too large to pass through latex condoms.

Proper usage entails:

• Not putting the condom on too tight at the end, and leaving 1.5 cm (3/4 inch) room at the tip for ejaculation. Putting the condom on snug can and often does lead to failure.
• Wearing a condom too loose can defeat the barrier.
• Avoiding inverting, spilling a condom once worn, whether it has ejaculate in it or not, even for a second.
• Avoiding condoms made of substances other than latex or polyurethane, as they don't protect against HIV.
• Avoiding the use of oil based lubricants (or anything with oil in it) with latex condoms, as oil can eat holes into them.
• Using flavored condoms for oral sex only, as the sugar in the flavoring can lead to yeast infections if used to penetrate.

Not following the first five guidelines above perpetuates the common misconception that condoms aren't tested or designed properly.

In order to best protect oneself and the partner from STIs, the old condom and its contents should be assumed to be still infectious. Therefore the old condom must be properly disposed of. A new condom should be used for each act of intercourse, as multiple usage increases the chance of breakage, defeating the primary purpose as a barrier.

Nonoxynol-9

Nonoxynol-9 a vaginal microbicide was hoped to decrease STD rates. Trials however have found it ineffective.^[9]

Diagnosis

STI tests may test for a single infection, or consist of a number of individual tests for any of a wide range of STIs, including tests for syphilis, trichomonas, gonorrhea, chlamydia, herpes, hepatitis and HIV tests. No procedure tests for all infectious agents.

STI tests may be used for a number of reasons:

• as a diagnostic test to determine the cause of symptoms or illness
• as a screening test to detect asymptomatic or presymptomatic infections
• as a check that prospective sexual partners are free of disease before they engage in sex without safer sex precautions (for example, in fluid bonding, or for procreation).
• as a check prior to or during pregnancy, to prevent harm to the baby
• as a check after birth, to check that the baby has not caught an STI from the mother
• to prevent the use of infected donated blood or organs
• as part of the process of contact tracing from a known infected individual
• as part of mass epidemiological surveillance

Not all STIs are symptomatic, and symptoms may not appear immediately after infection. In some instances a disease can be carried with no symptoms, which leaves a greater risk of passing the disease on to others. Depending on the disease, some untreated STIs can lead to infertility, chronic pain or even death.^[10] Early identification and treatment results in less chance to spread disease, and for some conditions may improve the outcomes of treatment.

There is often a window period after initial infection during which an STI test will be negative. During this period the infection may be transmissible. The duration of this period varies depending on the infection and the test.

Treatment

High risk exposure such as what occurs in rape cases may be treated prophylacticly using antibiotic combinations such as azithromycin, cefixime, and metronidazole.

An option for treating partners of patients (index cases) diagnosed with chlamydia or gonorrhea is patient-delivered partner therapy (PDT or PDPT), which is the clinical practice of treating the sex partners of index cases by providing prescriptions or medications to the patient to take to his/her partner without the health care provider first examining the partner.^[11]

Epidemiology

Age-standardized death from tuberculosis per 100,000 inhabitants in 2004.^[12]

     no data      less than 60      60-120      120-180      180-240      240-300      300-360      360-420      420-480      480-540      540-600      600-1000      more than 1000

STD incidence rates remain high in most of the world, despite diagnostic and therapeutic advances that can rapidly render patients with many STDs noninfectious and cure most. In many cultures, changing sexual morals and oral contraceptive use have eliminated traditional sexual restraints, especially for women, and both physicians and patients have difficulty dealing openly and candidly with sexual issues. Additionally, development and spread of drug-resistant bacteria (e.g., penicillin-resistant gonococci) makes some STDs harder to cure. The effect of travel is most dramatically illustrated by the rapid spread of the AIDS virus (HIV-1) from Africa to Europe and the Americas in the late 1970s.^[13]

Commonly reported prevalences of STIs among sexually active adolescent girls both with and without lower genital tract symptoms include chlamydia (10–25%), gonorrhea (3–18%), syphilis (0–3%), Trichomonas vaginalis (8–16%), and herpes simplex virus (2–12%).^{[citation needed]} Among adolescent boys with no symptoms of urethritis, isolation rates include chlamydia (9–11%) and gonorrhea (2–3%).^{[citation needed]}

In 1996, the World Health Organization estimated that more than 1 million people were being infected daily. About 60% of these infections occur in young people <25 years of age, and of these 30% are <20 years. Between the ages of 14 and 19, STDs occur more frequently in girls than boys by a ratio of nearly 2:1; this equalizes by age 20. An estimated 340 million new cases of syphilis, gonorrhea, chlamydia and trichomoniasis occurred throughout the world in 1999.^[14][15]

History

American propaganda poster targeted at World War II soldiers and sailors appealed to their patriotism in urging them to protect themselves. The text at the bottom of the poster reads, "You can't beat the Axis if you get VD." Images of women were used to catch the eye on many VD posters.

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 voluntary hospital for venereal diseases was founded in 1746 at London Lock Hospital.^[16] Treatment was not always voluntary: in the second half of the 19th century, the Contagious Diseases Act was used to arrest suspected prostitutes.

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 STDs, led to a public perception during the 1960s and 1970s that they have 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 a long asymptomatic period—during which time HIV (the human immunodeficiency virus, which causes AIDS) can replicate and the disease can be transmitted 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 replication of HIV for as long as possible. Contact tracing continues to be an important measure, even when diseases are incurable, as it helps to contain infection.

See also

• Bugchasing and giftgiving
• Microbicide
• STD Wizard
• Transmission (medicine)
• Zoophilia and health
• Autoimmunity, Autoimmune disease

References

External links

• Border Stories: Sex workers and HIV/AIDS in Tijuana, Mexico (VIDEO)
• SexInfo's Sexually Transmitted Infections Overview at University of California, Santa Barbara
• STD photo library at Dermnet
• Microbicides—Information from Our Bodies, Ourselves on the place of microbicides in the future of STI prevention.
• UNFPA: Breaking the Cycle of Sexually Transmitted Infections at UNFPA
• Dejucq N, Jégou B (June 2001). "Viruses in the mammalian male genital tract and their effects on the reproductive system". Microbiol. Mol. Biol. Rev. 65 (2): 208–31 ; first and second pages, table of contents. doi:10.1128/MMBR.65.2.208-231.2001. PMID 11381100. 
• Sexually Transmitted Infections from the National Institute of Allergy and Infectious Diseases
• "Sexual networks: implications for the transmission of sexually transmitted infections" at Massachusetts Institute of Technology
• "SxCheck 101, Basic Safe Sex Practices" (video). SxCheck. 2007. https://www.sxcheck.com/view/test/Sx101. Retrieved 2008-09-28.