Overview: Sexually Transmitted Infections

Sexually transmitted infections (STIs) or sexually transmitted diseases (STDs) are infections that spread either by vaginal intercourse, anal sex, or oral sex. Symptoms and signs may include vaginal discharge, penile discharge, dysuria, skin lesions (e.g., warts, ulcers) on or around the genitals, and pelvic pain. Some infections can lead to infertility and chronic debilitating disease. And some STIs can affect infants by vertical transmission. Diagnosis of STIs includes a combination of comprehensive medical and sexual history, assessing risk factors, focused genitourinary physical exam, and disease-specific laboratory tests/cultures. Treatment and prevention include a combination of antibiotic/antiviral agents and patient education on safe sex practices.

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  • 26 million new STIs diagnosed in the United States in 2018 
  • High-risk patient groups:
    • Adolescents and young adults ages 15–24 years (accounted for 50% of new STIs in 2018)
    • Men who have sex with men (MSM)
    • Racial and ethnic minorities 
  • HSV-2 and syphilis increase HIV infection risk.
  • STIs can result in serious reproductive consequences and adverse long-term health effects.
  • STIs reportable to state health departments:
    • Syphilis 
    • Chancroid
    • HIV
    • Gonorrhea
    • Chlamydia


Infections are mainly transmitted sexually, which can include unprotected vaginal, anal, or oral sex.


  • Chancroid (Haemophilus ducreyi)
  • Chlamydia and lymphogranuloma venereum (Chlamydia trachomatis)
  • Gonorrhea (Neisseria gonorrhoeae)
  • Granuloma inguinale or donovanosis (Klebsiella granulomatis)
  • Mycoplasma genitalium
  • Syphilis (Treponema pallidum)


  • Herpes simplex (herpes simplex virus, HSV types 1 and 2)
  • Hepatitis B virus: 
    • Sexual transmission
    • Other modes of transmission: blood/blood product exposure, mother-to-child
  • HIV
    • Sexual transmission
    • Other modes of transmission: blood/blood product exposure, breastfeeding
  • HPV
    • Most common STI worldwide
    • Genital warts: HPV-6 and 11
    • Anogenital squamous intraepithelial lesions: associated with 15 types, with HPV-16 as the most common


  • Pediculosis pubis or crab louse (Phthirus pubis)
  • Trichomoniasis (Trichomonas vaginalis)

Clinical Presentation

Bacterial STIs

Table: Clinical presentation of bacterial STIs
Type of STIOrganismSigns and symptoms
ChancroidHaemophilus ducreyi
  • Erythematous papule at the site of inoculation
  • Papules become ulcers.
  • Inguinal lymphadenopathy/buboes
ChlamydiaChlamydia trachomatis
  • Abnormal vaginal/penile discharge
  • Burning during urination
  • Bleeding in between periods
  • Proctitis in receptive anal intercourse
  • Epididymitis, prostatitis in men
GonorrheaNeisseria gonorrhoeae
  • Dysuria, urinary frequency
  • Discharge from the penis/vagina
  • Red or swollen urethra
  • Swollen or tender testicles
  • Sore throat
  • Proctitis
Granuloma inguinale or donovanosisKlebsiella granulomatis
  • Chronic progressive ulcerating disease (genital region)
  • Painless nodular lesions that ulcerate, commonly with a beefy-red base
Lymphogranuloma venereum (LGV)L1, L2, and L3 serovars of Chlamydia trachomatis
  • Genital ulcer
  • Inguinal lymphadenopathy/buboes
  • Vaginitis (discharge)
  • Proctocolitis
Mycoplasma genitalium infectionMycoplasma genitalium
  • Nongonococcal urethritis
  • Pelvic inflammatory disease
  • Proctitis
SyphilisTreponema pallidum
  • Ulceration of the urogenital tract (chancre)
  • Secondary and late syphilis symptoms will vary.

Viral STIs

Table: Clinical presentation of viral STIs
Type of STIOrganismSigns and symptoms
HerpesHSV-1 or 2If symptomatic, patients manifest:
  • Small fluid-filled blisters
  • Itching/tingling in the genital or anal area
  • Dysuria
  • Flu-like symptoms (e.g., fever)
Hepatitis BHepatitis B virus (HBV)Acute:
  • Abdominal pain, vomiting
  • Malaise
  • Jaundice
  • Dark urine
  • Asymptomatic
  • Chronic liver disease/cirrhosis
HIVTwo species of LentivirusDifferent disease stages include:
  • Primary infection
  • Asymptomatic infection
  • Symptomatic infection
  • AIDS
HPVDifferent types (6, 11, 16, and 18) of HPV
  • Genital warts around the anogenital area
  • Cervical cancer

Parasitic STIs

Table: Clinical presentation of parasitic STIs
Type of STIOrganismSigns and symptoms
TrichomoniasisTrichomonas vaginalis
  • Burning pain or itching in the genital area
  • Urethritis
  • Vaginitis
Pediculosis pubis or crab lousePthirus pubisPruritus in genital and perianal area


Diagnostic approach

Comprehensive sexual history:

  • Number of partners 
  • Types of sexual practices 
  • Types of protection used, if any 
  • Past history of STIs 
  • Prior history of pregnancy 
  • Vaccination history: 
    • Hepatitis A/B
    • HPV 
  • Travel history

Focused physical exam:

  • Head, eyes, ears, nose, throat (HEENT): Examine oral mucosa and lips for rashes or ulcers.
  • Abdominopelvic exam: Assess for lower abdominal or pelvic tenderness. 
  • Genitourinary exam: 
    • Palpate inguinal lymph nodes for nodules.
    • Genital exam for rashes, ulcers, exudate, warts 
    • Male: testicular exam to assess for swelling, tenderness

Specific tests

Specimen for testing is obtained from the site(s) of infection/lesion, which may include anogenital, lymph nodes, and oral areas.

Bacterial disease:

  • Chancroid: 
    • Culture from genital ulcers  
    • Rule out common etiologies of genital ulcer(s): herpes and syphilis
  • Chlamydia
    • Test of choice: nuclear acid amplification testing (NAAT) (PCR is a common method.) 
    • Culture has limited use.
  • Gonorrhea:
    • Test of choice: NAAT
    • Gram stain (microscopy)
    • Cultures (urethral, vaginal, pharyngeal, rectal)
  • Granuloma inguinale (donovanosis): 
    • Tissue biopsy sample 
    • Pathology would show Donovan bodies (bipolar-staining cytoplasmic inclusion bodies) 
  • Lymphogranuloma venereum: NAAT 
  • Mycoplasma genitalium: NAAT 
  • Syphilis: 
    • Nontreponemal tests: rapid plasma reagin and VDRL 
    • Confirmatory test: fluorescent treponemal antibody absorption (FTA-ABS)

Viral disease:

  • HSV-1 and 2: 
    • Test of choice: PCR
    • Serology
    • Viral culture
    • Tzanck smear 
  • HIV:
    • Screening: immunoassay that detects HIV-1 and HIV-2 antibodies and HIV-1 p24 antigen 
    • Confirmatory testing: specimens with reactive antigen/antibody immunoassay 
    • Acute infection: HIV RNA viral load 
  • HPV:
    • Detected in cervical specimen (as part of cervical cancer screening)
    • Also tested in oropharyngeal biopsy
  • Hepatitis B: 
    • Serologic markers (e.g., hepatitis B surface antigen and antibody)
    • PCR (HBV DNA)

Parasitic disease:

  • Trichomonas vaginalis: 
    • Microscopy (wet mount) shows motile trichomonads.
    • PCR 
    • Vaginal culture 
    • Cervical cytology
  • Pthirus pubis:
    • Demonstration of lice or nits (louse eggs) by direct or microscopic examination of hair shafts


Bacterial STIs

Table: Management of bacterial STIs
Type of STITreatment
ChancroidAzithromycin or ceftriaxone
ChlamydiaAzithromycin 1 g orally x 1 or doxycycline x 7 days (preferred in proctitis)
GonorrheaCeftriaxone 500 mg (with doxycycline if chlamydia has not been ruled out)
Granuloma inguinale or donovanosis
  • Azithromycin
  • Doxycycline
Lymphogranuloma venereum (LGV)Doxycycline
Mycoplasma genitalium infectionAzithromycin
SyphilisPenicillin G (parenteral)

Viral STIs

Table: Management of viral STIs
Type of STITreatment
  • Acyclovir, famciclovir, valacyclovir
  • Regimens for episodic and suppressive therapy
HPVCytodestructive therapy:
  • Podofilox 0.5% cream
  • Imiquimod 5% cream
Surgical therapy:
  • Cryotherapy
  • CO2 laser ablation
HIVCombination antiretroviral therapy with the following:
  • Nucleotide reverse transcriptase inhibitors
  • Nonnucleoside reverse transcriptase inhibitors
  • Integrase inhibitors
  • Protease inhibitors
Hepatitis B
  • Regimen can include pegylated interferon, tenofovir, or entecavir
  • Agents used depend on clinical considerations (e.g., pregnancy, cirrhosis)

Parasitic STIs

Table: Management of parasitic STIs
Type of STITreatment
  • Metronidazole or tinidazole
  • Treat sexual partners.
Pediculosis pubisTopical permethrin or topical pyrethrins with piperonyl butoxide


  • STI screening
  • Counseling on safe sex practices:
    • Educate on behaviors that increase risks of STIs.
    • Preventive measures (e.g., use of condom)
    • Importance of treating partners
  • Vaccination:
    • Hepatitis B
    • HPV
  • Prophylaxis:
    • Preexposure antiretroviral prophylaxis against HIV (HIV PrEP)
    • Postexposure antiretroviral prophylaxis against HIV (given within 72 hours)
  • Suppressive therapy for HSV reduces transmission of infection to uninfected partner.


  1. Centers for Disease Control and Prevention. (2021). Sexually transmitted infections prevalence, incidence, and cost estimates in the United States. Retrieved April 21, 2021, from https://www.cdc.gov/std/statistics/prevalence-2020-at-a-glance.htm
  2. Ghanem, K. (2021) Clinical manifestations and diagnosis of Neisseria gonorrhoeae infection in adults and adolescents. UpToDate. Retrieved April 21, 2021, from https://www.uptodate.com/contents/clinical-manifestations-and-diagnosis-of-neisseria-gonorrhoeae-infection-in-adults-and-adolescents
  3. Ghanem, K. (2019). Screening for sexually transmitted infections. UpToDate. Retrieved April 17, 2021, from https://www.uptodate.com/contents/screening-for-sexually-transmitted-infections
  4. Goldstein, A., Goldstein, B. (2021) Pediculosis pubis and pediculosis ciliaris. UpToDate. Retrieved April 21, 2021, from https://www.uptodate.com/contents/pediculosis-pubis-and-pediculosis-ciliaris
  5. Hamill, M. (2021) Lymphogranuloma venereum. UpToDate. Retrieved April 21, 2021, from https://www.uptodate.com/contents/lymphogranuloma-venereum
  6. Hicks, C. (2021) Chancroid. UpToDate. Retrieved April 21, 2021, from https://www.uptodate.com/contents/chancroid
  7. Lok, A. (2021) Hepatitis B virus: overview of management. UpToDate. Retrieved April 21, 2021, from https://www.uptodate.com/contents/hepatitis-b-virus-overview-of-management
  8. Martin, D. (2021) Mycoplasma genitalium infection in men and women. UpToDate. Retrieved April 21, 2021, from https://www.uptodate.com/contents/mycoplasma-genitalium-infection-in-men-and-women
  9. Palefsky, J. (2021) Human papillomavirus infections: epidemiology and disease associations. UpToDate. Retrieved April 21, 2021, from https://www.uptodate.com/contents/human-papillomavirus-infections-epidemiology-and-disease-associations
  10. Simma-Chiang, V. (2021). Sexually Transmitted Infection. AUA Core Curriculum. Retrieved April 18, 2021, from https://auau.auanet.org/core 
  11. Sobel, J., Mitchell, C. (2021) Trichomoniasis. UpToDate. Retrieved April 21, 2021, from https://www.uptodate.com/contents/trichomoniasis
  12. Teo, E., Lok, A. (2021) Epidemiology, transmission and prevention of hepatitis B infection. UpToDate. Retrieved April 21, 2021, from https://www.uptodate.com/contents/epidemiology-transmission-and-prevention-of-hepatitis-b-virus-infection

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