Overview of sexually transmitted infections

Last reviewed: 30 Aug 2023
Last updated: 06 Jun 2023

This page compiles our content related to sexually transmitted infections. For further information on diagnosis and treatment, follow the links below to our full BMJ Best Practice topics on the relevant conditions and symptoms.



Chlamydial genital infection is the most frequently reported STI in the US.[1] Infection is usually asymptomatic in both men and women. Nonculture diagnostic techniques such as nucleic acid amplification tests are recommended.[2] Lack of or inadequate treatment risks possible ascending infection and further complications, as well as possible spread of the infection to sexual partners.

The most commonly reported STI after chlamydial infection.[1][3] Classic presentation is a man with a urethral discharge; women are often asymptomatic but may have vaginal discharge. If left untreated, Neisseria gonorrhoeae can disseminate to cause skin and synovial infections. Rarer complications include meningitis, endocarditis, and perihepatic abscesses. High rates of antimicrobial resistance have been reported, and antibiotic treatment should be guided by local and national guidelines.

A common sexually transmitted infection caused by a spirochetal bacterium. Clinical presentation is often asymptomatic but can manifest in a number of ways. Diagnosis is usually straightforward after clinical exam and serologic testing; treatment is with penicillin. Untreated syphilis facilitates HIV transmission and causes considerable morbidity, such as cardiovascular and neurologic disease, as well as a congenital syndrome in newborn babies.[2][4]

Lymphogranuloma venereum (LGV) is caused by Chlamydia trachomatisgenovars/serovars L1, L2, or L3. The primary manifestation of infection is a painless penile or vulvar inflammation and ulceration at the site of inoculation, often unnoticed by the patient.[5][6] Chronic inflammation can lead to scarring and fibrosis causing lymphedema of the genitals, or formation of strictures and fistulae if anorectal involvement. Identification of LGV serovars of Chlamydia trachomatis from the swab of a genital ulcer or aspiration of a bubo provides definitive diagnosis.[2]

A sexually transmitted infection caused by the fastidious, gram-negative coccobacillus Haemophilus ducreyi, which is most common in resource-poor countries.[7][8] Classically presents with the acute onset of a painful genital ulcer with fluctuant lymphadenitis (bubo formation). Chancroid is an important cofactor in HIV transmission, and HIV status must be assessed.[2] Most cases resolve with antibiotic therapy; recurrence is rare.

An acute ascending polymicrobial infection of the female upper genital tract that is frequently associated with Neisseria gonorrhoeae or Chlamydia trachomatis.[9] Pelvic inflammatory disease includes endometritis, salpingitis, tubo-ovarian abscess, and pelvic peritonitis. May be asymptomatic or present with fever, vomiting, back pain, dyspareunia, bilateral lower abdominal pain/discomfort, abnormal vaginal odor, itching, bleeding, or discharge.[10] Antibiotic therapy generally targets gonorrhea, chlamydia, and anaerobic bacteria.[2]

Typically presents with dysuria, urethral discharge, and/or pruritus at the end of the urethra. Neisseria gonorrhoeae and Chlamydia trachomatis are the most common causes; Mycoplasma genitalium andTrichomonas vaginalis are less common.[2][11] Diagnostic tests include Gram stain and culture of the urethral discharge and nucleic acid amplification tests.

Common and often asymptomatic, but if left undiagnosed or untreated can result in pelvic inflammatory disease (PID), which can in turn lead to substantial long-term effects such as infertility and chronic pelvic pain. While Neisseria gonorrhoeae and Chlamydia trachomatis are the most commonly isolated organisms, in most cases no etiologic organism is identified.[2]

Inflammation of the vagina due to changes in the composition of the vaginal micro-environment from infection, irritants, or hormonal deficiency (e.g., atrophic vaginitis). Common symptoms include discharge, pruritus, and dyspareunia. Bacterial vaginosis is the leading cause of vaginitis; other common infectious causes include trichomoniasis and candidiasis.[12]

In sexually active men, epididymitis is most commonly caused by Neisseria gonorrhoeaeChlamydia trachomatis, or Mycoplasma genitalium.[13] In older men (>35 years), the causative organisms are often enteric pathogens, and epididymitis may be associated with bladder outlet obstruction, recent instrumentation of the urinary tract, or systemic illness. Treatment relies on supportive measures in conjunction with appropriate antibiotics.

Infection with herpes simplex virus type 1 (HSV-1) or HSV type 2 (HSV-2) can cause oral, genital, or ocular ulcers. Less commonly, primary or recurrent HSV infections may also present at other sites with neurologic, ocular, hepatic, or respiratory complications. HSV establishes latency and periodically reactivates. Most reactivations are asymptomatic but can result in transmission of the virus. The classic clinical presentation of vesicles progressing to painful ulcers is unusual; atypical and mild symptoms are common, and most people have unrecognized disease.[14][15]

The most prevalent form of viral genital mucosal lesions, caused by infection with several types of human papillomavirus (HPV).[16] Lesions are usually 1 to 3 mm, flesh-colored, whitish, or hyperpigmented, discrete, sessile, smooth-surfaced exophytic papillomas, or they may coalesce into larger plaques. Diagnosis is based on clinical presentation.[16]

Caused by a retrovirus that infects and replicates in human lymphocytes and macrophages, eroding the integrity of the human immune system over a number of years. Diagnosis is established using an initial HIV antibody or combination antibody/antigen test and confirmed using a more specific test. Patients should be clinically staged according to World Health Organization or US Centers for Disease Control and Prevention criteria. All patients infected with HIV, regardless of CD4 cell count, should start antiretroviral therapy as soon as possible.[17]

Post-exposure prophylaxis (PEP) reduces the probability of HIV transmission by 80% when taken within 72 hours following exposure, and for a full 28-day course as prescribed.[18][19][20] The efficacy of PEP and the potential toxicities and adverse effects of the treatment need to be fully explained to the patient; counseling is an important step in patient management.

A human papillomavirus (HPV)-related malignancy, preventable by HPV vaccination, screening, and treatment of high-grade dysplasia. Cervical cancer screening by cytology (Pap testing) alone, Pap and HPV co-testing, or primary HPV testing may detect pre-invasive disease.[2][21] Patients with advanced disease may present with abnormal vaginal bleeding, postcoital bleeding, vaginal discharge, pelvic or back pain, dyspareunia, or obstructive uropathy.

Reactive arthritis (ReA) is an inflammatory arthritis that occurs after exposure to certain gastrointestinal and genitourinary infections.[22] The classic triad of postinfectious arthritis, nongonococcal urethritis, and conjunctivitis is frequently described but found in only a minority of cases and not required for diagnosis.[22] There is no specific test for diagnosing ReA. Rather, a group of tests is used to confirm the suspicion in someone who has clinical symptoms suggestive of an inflammatory arthritis in the postvenereal or postdysentery period. Treatment is aimed at symptomatic relief and preventing or halting further joint damage.

Sexual assault is common and can affect adults of any age, as well as children. Young women are most at risk, but males are also sexually violated. Time elapsed since the most recent sexual assault, and the pubertal status in children, determine the appropriate management strategy in the acute setting.[23][24]

Most people with hepatitis B are asymptomatic, although some will present with complications such as cirrhosis, hepatocellular carcinoma, or liver failure. People from endemic areas, injection drug users, and those with high-risk sexual behaviors are at an increased risk of infection. Serologic markers are essential in making the diagnosis and evaluating disease activity, including differentiating between people with acute and chronic infection and chronic asymptomatic carriers. Therapy for chronic infection includes nucleoside/nucleotide analogs, interferon-alfa, and pegylated interferon-alfa.[25]

Most common routes of transmission are through illicit injection drug use (sharing used needles) and transfusion of contaminated blood products. Most infections are asymptomatic; however, hepatic inflammation is often present and can lead to progressive hepatic fibrosis. The goal of treatment is to eradicate the virus, achieve a sustained virologic response, and prevent disease progression. Oral direct-acting antiviral therapies are standard treatment. Long-term complications include cirrhosis or hepatocellular carcinoma.[26]

Vaginal discharge is one of the most common reasons for gynecologic visits; it may be physiologic or pathologic. Pathologic causes are commonly due to infection, mainly bacterial vaginosis, vulvovaginal candidiasis, and trichomoniasis. The true prevalence of this condition is uncertain because vaginitis, which encompasses the symptom vaginal discharge, is often asymptomatic, self-diagnosed, and self-treated.[2]

Dyspareunia, or painful sexual intercourse, is a common symptom among women. It may result from various causes, including inflammatory, infectious, mucosal, and musculoskeletal conditions.

Dysuria is a common condition but can be challenging to diagnose, as it is often present in conjunction with other lower urinary tract symptoms. Although urinary tract infection is the most common cause, any infectious or inflammatory condition affecting the genitourinary system may cause dysuria.



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