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Sexually transmitted infections


Medical Professionals

Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find the Sexually transmitted infections article more useful, or one of our other health articles.

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What are sexually transmitted infections?

The Venereal Diseases Act of 1917 defined three sexually transmitted diseases: syphilis, gonorrhoea and chancroid.

  • In the UK, chancroid is unimportant and often forgotten although it is still troublesome in some parts of Africa.

  • Syphilis ebbed but has been resurgent in recent years and the prevalence of gonorrhoea is often taken as an index of the degree of promiscuity in the community.

The generic term for venereal disease (VD) was changed to sexually transmitted diseases (STDs) and the VD clinics became special clinics as new euphemisms were devised to hide the embarrassment of society.

More recently the speciality was called genitourinary medicine (GUM). The term sexually transmitted infections (STIs) is now used in preference to STDs because, strictly speaking, infections are not always associated with symptoms, whereas diseases are.

Sexually transmitted diseases

The number of diseases that are usually transmitted by sexual intercourse or which may be transmitted by that route, is much greater than the three defined by the Venereal Disease Act.1 The following are classified as STIs:2

Many of these diseases are covered in more detail under the specific appropriate article.

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STI epidemiology

After a surge in STIs during the First World War, there was a lull between wars and another surge during the Second World War. Some young men going off to war sought comfort in a way that put them at risk of acquiring STIs.

The 1960s saw an unprecedented availability of 'the pill' and increased promiscuity, without barrier contraception. The slogan of the young was 'make love, not war' and the use of drugs became more prevalent. There was an unrealistic expectation that antibiotics could cure all STIs. The advent of HIV/AIDS reminded clinicians of the limitations of antibiotics, and fear of infection (and fewer episodes of casual sex) led to a brief drop in rates of gonorrhoea infection.

Younger people continue to experience the highest rates of STIs. Among heterosexuals attending GUM clinics, 63% with chlamydia, 55% with gonorrhoea, 52% with genital warts and 42% with genital herpes were aged 15-24 .

The impact of STIs remains greatest in young heterosexuals aged 15-24 years; black ethnic minorities; and gay, bisexual and other men who have sex with men (MSM).3

Some of the increases in gonorrhoea and chlamydia diagnoses among young people may reflect increased attendance of young people at GUM clinics and, for chlamydia, increased and more sensitive testing. Diagnoses, however, still underestimate the true level of infection in the UK, as many infections are asymptomatic.

The latest statistics (2019) from Public Health England show:3

  • There were 468,342 diagnoses of STIs made in England -a 5% increase since 2018.

  • There were 70,936 diagnoses of gonorrhoea reported - a 26% increase since 2018. There were 7,982 diagnoses of syphilis reported - a 10% increase since 2018.

  • There were 5,311 diagnoses of Mycoplasma genitalium reported - a 196% increase since 2018; the increase reflects a rise in the availability of testing.

  • There were 149 diagnoses of first episode genital warts in 15 to 17 year old girls -a 23% decrease relative to 2018, and 90 diagnoses of first episode genital warts in same aged heterosexual boys, an 11% decrease relative to 2018; this is a continuation of the steep decline observed since 2014 and is largely due to the high coverage National HPV Vaccination Programme in schools.

Modes of STI transmission

To make a meaningful analysis of the facts and figures, it is important to look at the various ways by which the diseases may be spread. Not all such diseases are always spread by sexual activity. Transmission of infection can occur, for example, by intravenous drug misuse. Some diseases can be vertically transmitted from mother to child.

The pool of undiagnosed disease in a population is also an important problem. Such people can spread infection unwittingly. The number of people carrying undiagnosed infection varies according to the disease concerned. In many cases, infection remains undiagnosed as the individual is asymptomatic. The disease may be more likely to produce symptoms in one sex than the other but it remains contagious. For example, a man may readily see a primary chancre of syphilis on his glans whilst a woman is unaware of one on her cervix. Candida may cause vaginal discharge and pruritus vulvae but often in men causes no symptoms.

STI risk factors

The risk of acquiring STIs is greatest in those who are have multiple sexual partners, especially if they do not use barrier contraceptives. Other factors associated with a higher incidence of STIs are:2 4 5

  • Young age.

  • Failure to use barrier contraceptives.

  • Casual sexual relationships.

  • Men having sex with men.

  • Intravenous drug use.

  • African origin (sub-Saharan Africa).

  • Social deprivation.

  • Prostitution.

  • Poor access to advice and treatment of STIs.

It is important to have some perspective on what constitutes 'normal' sexual activity. For example, since the 1990s there has been a trend to have first sexual intercourse earlier, an increase in the number of people having multiple partners and an increase in the number of men having sex with men.6

STI presentation

Most STIs are best treated in a GUM clinic, as they have expertise in diagnosis and treatment as well as the ability to perform contact tracing. However, many patients with STIs present to GPs and it is essential that the initial advice and information should be correct even if definitive diagnosis and treatment are not given.

Sexual history

A sexual history is essential to guide decisions about management, or additional examinations or tests that might benefit the patient with suspected STI. It is essential that privacy be maintained. See the separate Sexual History Taking article.

Taking a sexual history can present problems in general practice for many reasons - for example:

  • Patients are often reluctant to talk about their condition because of the stigma associated with STIs.

  • Patients may not appreciate that their symptoms are the result of an STI.

  • Inexperience or lack of knowledge amongst GPs.

  • Colluding with patients to 'play down' symptoms.

  • Lack of time to assess adequately.

  • The sensitivity of the subject for doctor and patient (particularly when the doctor has known the patient and family for many years).

  • Problems posed by the need for intimate examinations (use of chaperones, for example).


  • Avoid the possibility of others walking in on the examination.

  • It is usually advisable to have a chaperone when examining patients irrespective of gender.

  • It is appropriate to begin with a general assessment, including vital signs, inspection of the skin and detection of signs of systemic disease.

  • Remember basics before examining:

    • Ensure that the examination can be conducted in privacy.

    • Wash hands well (water and soap).

    • Use a sheet or clothing to cover the patient.

    • Position the patient and ensure they are comfortable.

    • Explain what you are about to do.

    • Put on a suitable examination glove.

    • Carry out the examination in good light.

Female patients
There are three components to the female genital examination (assuming speculum/equipment are available):

  • External genital examination:

    • Inspect the perineum and anus - using the gloved hand.

    • Look for lumps, swelling, lymphadenopathy, abnormal discharge, sores, ulcers, tears and scars around the genitals and in between the skin folds of the vulva.

  • Speculum examination for:

    • Vaginal discharge and redness of the vaginal walls (vaginitis).

    • Ulcers, sores or blisters.

    • Cervical abnormalities (tumours, contact bleeding or discharge).

  • Bimanual examination:

    • Lower abdominal tenderness (when pressing with the outside hand).

    • Cervical motion tenderness (often evident from facial expression) when the cervix is moved from side to side with the fingers of the gloved hand in the vagina.

    • Uterine or adnexal tenderness when pressing the outside and inside hands together.

    • Any abnormal swelling (remember pregnancy, uterovaginal prolapse, ovarian cysts, tumours, etc).

Male patients

  • Ask the patient to stand up and lower his underpants to his knees (or examine with the patient in a lying position if preferred).

  • Palpate the inguinal region for enlarged lymph nodes or buboes.

  • Palpate the scrotum, feeling for the testis, epididymis and spermatic cord on each side.

  • Examine the penis, noting any rashes or sores.

  • Ask the patient to pull back the foreskin if present and look at the glans penis and urethral meatus.

  • If there is no obvious discharge, ask the patient to milk the urethra.

  • Ask the patient to turn his back to you and bend over, spreading his buttocks slightly. This can also be done with the patient lying on his side with the top leg flexed up towards his chest.

  • Examine the anus for ulcers, warts, rashes, or discharge.

Continue reading below

STI diagnosis

History and examination may lead to the detection of STI which may be entirely unsuspected by the patient.


Links to UK national guidelines are available from the British Association for Sexual Health and HIV (BASHH) website.

More extensive testing is available by referral to a local GUM clinic. All pathology laboratories have their own operating policies. It is often important to discuss tests with the local laboratory. The processing of samples varies considerably and may depend on the clinical information provided. There are other guidelines produced from Public Health England and the Association of Medical Microbiologists to inform healthcare professionals working in laboratories.

Tests vary around the country, so you should be familiar locally with:

  • Which swabs to take.

  • Where to swab.

  • How to take a sample.

  • Transport issues.

  • The sensitivity and specificity of tests (as false positives and false negatives occur).

If there is a particular local need, consider:

  • Going on a Sexually Transmitted Infection Foundation (STIF) course.8

  • Talking to your local GUM clinic and microbiology laboratory.

What to test for and when2

HIV testing
Determine whether you practise in an area of high HIV prevalence (>2 per 1,000; the local GUM specialist can advise).

In areas of high prevalence, HIV testing should be offered to:

  • All newly registered patients

  • All 'at-risk' patients:

    • Anyone with an STI.

    • Men who have sex with men.

    • Those buying/selling sex.

    • Those from countries of high HIV prevalence.

    • Intravenous drug users.

    • Any sexual partner of the above.

  • All those with 'clinical indicator diseases'.

In areas of low prevalence, HIV testing should be offered to:

  • 'At-risk' patients.

  • All those with 'clinical indicator diseases'.

For more information about clinical indicator diseases, see the separate Human Immunodeficiency Virus (HIV) article.

The HIV test

  • In-depth counselling is not necessary.

  • Emphasise the benefits of testing (earlier diagnosis leads to better prognosis, as effective treatment is now available).

  • Reassure patients that insurance companies do not enquire about negative results.

  • Send 10 mls of clotted blood to Virology, marked 'HIV test'.

  • Document how the patient will be informed of the results.

  • Re-test if within the three-month window period.

  • If negative, discuss risk reduction. If positive, refer according to local pathways - urgency to depend on the clinical status of the patient.

Asymptomatic patients

Those at high risk of STIs are:

  • Under the age of 25; and/or

  • With a new sexual partner within the previous 12 months.


  • Test for Chlamydia trachomatis.

  • In areas of high prevalence of gonorrhoea (or if there is a local outbreak) a test for Neisseria gonorrhoeae should be undertaken in high-risk patients.

  • Trichomonas (should be tested for but relatively uncommon and usually symptomatic).

  • It is not possible to exclude herpes genitalis by 'screening'. Only test for herpes if lesions are present.

  • In asymptomatic patients there is no value in taking samples for bacterial vaginosis or candida (neither of which is strictly sexually transmitted).

High-risk groups (above):

  • Urine test for chlamydia and gonorrhoea.

  • A positive test for gonorrhoea should prompt referral to a GUM clinic for a gonorrhoeal culture to be obtained (this confirms diagnosis and gives antibiotic sensitivities prior to treatment).

Symptomatic patients


  • Symptomatic women in high-risk groups (aged under 25 and with a new sexual partner within the previous 12 months): test for:

    • Gonorrhoea

    • Chlamydia

    • Bacterial vaginosis

    • Trichomonas

    • Candida

  • Symptomatic women aged over 25 years:

    • A risk assessment should be undertaken.

    • Test for chlamydia and gonorrhoea whatever the genital symptoms (if not previously performed).

    • The most common cause of vaginal discharge will be either bacterial vaginosis or candida.

    • If there has been no change in sexual partner since the last test for chlamydia/gonorrhoea then empirical treatment based on the pH paper result, with further investigation if the symptoms do not resolve, should suffice. For normal vaginal pH, treat as if candida; for elevated pH (5.0), treat for bacterial vaginosis.

    • If there are urinary symptoms and/or lower abdominal pain, sexually transmitted organisms should be excluded in the high-risk group and considered on the basis of a risk assessment in those over the age of 25 with no change of partner.


  • Urethral discharge and/or dysuria usually indicate an STI.

  • Ideally, a diagnosis of urethritis needs to be made for which microscopy of a Gram-stained slide is required. See the separate Gonorrhoea article.

  • Tests for gonorrhoea and chlamydia are recommended.

  • Men with testicular swelling or discomfort should have STI excluded. The most common cause of these symptoms in men aged under 40 is C. trachomatis. A midstream specimen of urine (MSU) is also advisable to exclude a urinary tract organism as a cause of this, especially in those aged over 40.

STI management 9

  • Details can be found in the articles linked above under the heading 'Diseases which may be transmitted sexually'.

  • Management of STIs in children and young people is beyond the scope of this article.10

  • Anyone who is being treated for an STI should abstain from sexual activity until treatment (their own and their partner's) is complete.

  • Partner notification is difficult to undertake comprehensively in primary care and is best left to specialist GUM services.2

  • Single-dose antibiotics are often used, where possible, to improve compliance.

STI prevention11

The social stigma of having an STI is enormous and the GUM clinics, since their origin, have been discreet and kept anonymity for their patients. Patients are often given a number so that they do not have to present with a name. They tend to have a discreet entrance in a distant part of the hospital and, to ensure compliance, the drugs they dispense are exempt from prescription charges. It is the only part of the NHS that will not routinely inform the patient's GP of attendance.

Despite anonymity and sensitivity of diagnosis, clinics will attempt to trace contacts of those with STIs. This is a very important role. The Golding prosecution involved the prosecution of David Golding who was jailed for 14 months after failing to inform a partner - who subsequently became infected - that he had genital herpes. There is concern amongst public health experts that this will inhibit patients with concerns from seeking help.2 Golding appealed in 2014 and lost his appeal. The Crown Prosecution Service published guidance as to when it would be appropriate to prosecute an individual for grievous bodily harm under the relevant legislation (the Offences against the Person Act 1861). It would need to be demonstrated that the person was reckless in foreseeing that a sexual partner might be exposed to infection via unprotected sex but persisted in taking the risk. Furthermore, actual transmission of STI had to occur. It was expected that actual prosecutions would be few and far between.

PHE guidance recommends that local authorities ensure continued access to chlamydia screening for 15- to 24-year-olds through a range of settings including internet services.3 This should include partner notification and retesting those who are diagnosed, to ensure reductions in onward transmission and subsequent harm.

The guidance also also recommends statutory, high-quality Relationships Education in primary schools and Relationships and Sex Education (RSE) in secondary schools, to inform a positive attitude to relationships and sexual health; it is hoped that RSE will also equip young people with the skills to maintain their sexual health and overall well-being.

Editor's note

Dr Krishna Vakharia 27th June 2022

Reducing sexually transmitted infections12

The National Institute for Health and Care Excellence (NICE) has recently published guidance on reducing sexually transmitted infections, most notably by targeting at-risk groups and advising where local services are, and emphasising they are free in the UK to encourage uptake. They aim to reduce stigma across the board. They also encourage increasing access by having clinics in easier-to-reach places and at more convenient times.

HPV and hepatitis A and B vaccination in gay, bisexual and other men who have sex with men

NICE has emphasised opportunistic discussions about HPV and hepatitis whilst encouraging vaccinations in all groups who are eligible but especially those who are gay, bisexual or other men who have sex with men. Of note, clinicians should give them information on HPV, hepatitis A and hepatitis B vaccination, including:

The diseases and their potential severity.

The risks and benefits of vaccination, including individual benefits and, if appropriate, population benefits (protecting other people in their community).

The importance of having all doses of a vaccination course.

Pre-exposure prophylaxis (PrEP) for HIV

Within the guidance there is emphasis on ensuring vulnerable groups are aware of PrEP and how to access this. Those groups are trans people, cisgender women, and young people (age 16-24) amongst others.

Of note, trans people undergoing medical transition should be advised that there are no clinically significant interactions expected between PrEP and the common hormones used in this process, and that using PrEP is not expected to affect their transition.

Prescribing PrEP

Offer PrEP to people at higher risk of HIV (use BHIVA/BASHH guidelines).

Encourage barrier methods such as condom use.

Support people who are taking PrEP to get regular HIV testing and STI screening (every three months).

Give people taking PrEP information and education on effectiveness, adherence, side-effects and monitoring risks.

Follow up people taking PrEP.

Monitor the kidney function of people taking PrEP, and any other adverse health events.

Help people taking PrEP to maximise adherence to treatment.

Further reading and references

  1. Garcia MR, Wray AA; Sexually Transmitted Infections
  2. Sexually Transmitted Infections in Primary Care; Royal College of General Practitioners and British Association for Sexual Health and HIV (Apr 2013)
  3. Sexually transmitted infections and screening for chlamydia in England; Public Health England, December 2019
  4. Manhart LE, Aral SO, Holmes KK, et al; Influence of study population on the identification of risk factors for sexually transmitted diseases using a case-control design: the example of gonorrhea. Am J Epidemiol. 2004 Aug 15;160(4):393-402.
  5. Gaspari V, D'Antuono A, Bellavista S, et al; Prostitution, sexual behavior and STDs. G Ital Dermatol Venereol. 2012 Aug;147(4):349-55.
  6. Sexually transmitted infections and under-18 conceptions: prevention; NICE Public Health Guidance (February 2007)
  7. BASHH Clinical Effectiveness Group Guidelines; British Association for Sexual Health and HIV
  8. BASHH Training Courses; The STI Foundation (STIF)
  9. Workowski KA, Bachmann LH, Chan PA, et al; Sexually Transmitted Infections Treatment Guidelines, 2021. MMWR Recomm Rep. 2021 Jul 23;70(4):1-187. doi: 10.15585/mmwr.rr7004a1.
  10. Management of sexually transmitted infections and related conditions in children and young people; British Association for Sexual Health and HIV (2021).
  11. Health matters: preventing STIs; Public Health England, GOV.UK
  12. Reducing sexually transmitted infections; NICE guideline (June 2022)

Article history

The information on this page is written and peer reviewed by qualified clinicians.

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