Sexually Transmitted Infections (STIs) are infections passed from person to person primarily through sexual contact (vaginal, anal, or oral sex). They can be caused by bacteria, viruses, or parasites.
 

Many STIs are asymptomatic, meaning a person can harbor and transmit an infection without having any noticeable signs or symptoms. Regular screening may be appropriate for certain sexually active individuals, as untreated STIs can lead to long-term health complications such as pelvic inflammatory disease (PID), chronic pelvic pain, infertility, ectopic pregnancy, increased risk of HIV transmission, and organ damage. 

Although some types of STIs may resolve naturally through the body's immune response, others can persist indefinitely or cause serious complications if left untreated. Fortunately, many STIs are curable with appropriate treatment. Early detection and management are essential for preventing complications and reducing transmission to others.

STI treatment guidelines have been established by the CDC.
 

Bacterial & Parasitic STIs (Curable)

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Chlamydia (Chlamydia trachomatis)
 

• Overview: The most commonly reported bacterial STI. Frequently asymptomatic in both men and women (often called a "silent" infection).

  • Women: Abnormal vaginal discharge, burning with urination (dysuria), post-coital bleeding, or lower abdominal pain.

  • Men: Clear or cloudy penile discharge, burning with urination, or testicular pain/swelling (epididymitis).

• Complications: Pelvic Inflammatory Disease (PID), ectopic pregnancy, tubal factor infertility, and reactive arthritis.

• First-Line Treatments:

  • Doxycycline: 100 mg orally twice daily for 7 days

Gonorrhea (Neisseria gonorrhoeae)
 

• Overview: A bacterial infection affecting the mucous membranes of the urethra, cervix, rectum, throat, and eyes. Known for developing antibiotic resistance.

• Key Symptoms:

  • Women: Often mild or asymptomatic; may cause dysuria, increased vaginal discharge, or intermenstrual bleeding.

  • Men: Profuse, thick yellow/green penile discharge, severe dysuria, and testicular pain.

  • Extragenital: Sore throat (pharyngeal) or rectal discharge/discomfort.

• Complications: Disseminated Gonococcal Infection (DGI) causing arthritis and skin lesions, PID, and infertility.

• First-Line Treatment:

  • Ceftriaxone: 500 mg intramuscularly (IM) in a single dose (for individuals weighing under 150 kg). If chlamydial infection has not been ruled out, co-treatment with oral Doxycycline is added.

Syphilis (Treponema pallidum)
 

• Overview: A complex, multi-stage bacterial infection that progresses through distinct clinical phases if left untreated.

• Stages & Key Features:

  • Primary Syphilis: A single, painless sore (chancre) appearing at the site of infection 1 to 3 weeks after exposure. Highly contagious; heals spontaneously without treatment.

  • Secondary Syphilis: Widespread, non-itchy skin rash (characteristically including the palms of the hands and soles of the feet), moist genital lesions (condylomata lata), fever, and swollen lymph nodes.

  • Latent Syphilis: Asymptomatic phase following secondary symptoms; can last for years.

  • Tertiary Syphilis: Develops years later, causing destructive tissue lesions (gummas), cardiovascular complications (aortic aneurysms), and neurosyphilis (dementia, gait abnormalities).

Trichomoniasis (Trichomonas vaginalis)
 

• Overview: The most common non-viral STI, caused by a microscopic protozoan parasite.

• Key Symptoms:

  • Women: Diffuse, frothy, yellow-green vaginal discharge with a strong fishy odor, vulvar itching/redness, dysuria, and a classic "strawberry cervix" seen on pelvic exam.

  • Men: Usually asymptomatic; may cause mild urethral irritation, burning after urination or ejaculation, or slight discharge.

• First-Line Treatments:

  • Metronidazole (Flagyl) or Tinidazole: 2 g orally in a single dose, or Metronidazole 500 mg twice daily for 7 days (preferred in women to lower recurrence rates).

Viral STIs (Manageable, Not Curable)
 

Viral STIs cannot be completely eradicated by antibiotics, but antiviral medications can control viral replication, reduce symptom severity, prevent outbreaks, and significantly lower transmission risk. Many people may still shed these viruses without an outbreak or signs present. 
 

Human Papillomavirus (HPV)
 

• Overview: The most common STI globally, encompassing over 150 related virus strains. 

• Clinical Manifestations:

  • Low-Risk Strains (Types 6 & 11): Cause benign genital warts (condylomata acuminata)—soft, cauliflower-like growths on the vulva, cervix, penis, scrotum, or perianal area.

  • High-Risk Strains (Types 16 & 18): Cause oncogenic cellular changes leading to cervical cancer, as well as anal, penile, vaginal, vulvar, and oropharyngeal cancers.

• Management & Prevention:

  • Wart Treatments: Topical patient-applied therapies (Podofilox, Imiquimod) or provider-applied treatments (cryotherapy, trichloroacetic acid, or surgical excision).

  • Cancer Prevention: Routine cervical cytology screening (Pap smears) and HPV DNA testing.

  • Vaccination: Gardasil 9 vaccine protects against major low-risk and high-risk HPV strains; recommended for females and males aged 9 through 26 (and up to age 45 based on clinical decision-making).

Herpes Simplex Virus (HSV-1 & HSV-2)
 

• Overview: A chronic viral infection typically characterized by periodic, painful outbreaks of fluid-filled vesicles that rupture into painful ulcers. 

  • HSV-1: Traditionally causes oral herpes (cold sores), but increasingly accounts for genital herpes through oral-genital contact. Genital HSV-1 cases are less likely to cause recurrent outbreaks. 

  • HSV-2: Almost exclusively causes genital herpes.

• Key Symptoms: Painful, clustered fluid-filled blisters on an erythematous base, preceded by a tingling or burning sensation (prodrome). Initial outbreaks often feature systemic flu-like symptoms and localized lymphadenopathy. Both can potentially spread to other body sites and cause severe, life-threatening complications. Autoinoculation from touching an active lesion can transfer the virus to the eye causing potential vision loss or to the fingers, leading to a painful lesion known as herpetic whitlow. Also, the virus can travel into the central nervous system, where HSV-1 is the primary cause of fatal herpes simplex encephalitis and HSV-2 can trigger aseptic meningitis. In immunocompromised individuals or newborns exposed during childbirth, HSV can disseminate systemically to cause mulit-organ failure. 

• First-Line Treatments:

  • Acyclovir, Valacyclovir (Valtrex), or Famciclovir: Antiviral therapies used as episodic treatment (started at the onset of symptoms) or suppressive therapy (taken daily to reduce outbreak frequency and asymptomatic viral shedding).

Human Immunodeficiency Virus (HIV)
 

• Overview: A retrovirus that attacks the body's CD4 T-lymphocytes (immune cells), weakening immune defense and leading to Acquired Immunodeficiency Syndrome (AIDS) if untreated.

• Key Symptoms:

  • Acute HIV Infection: Flu-like illness (fever, rash, sore throat, swollen lymph nodes) occurring 2 to 4 weeks after exposure.

  • Chronic HIV Infection: Often asymptomatic for years while the virus gradually depletes CD4 cells.

• Management & Prevention:

  • Treatment: Antiretroviral Therapy (ART)—a daily regimen combining multiple antiviral drugs to suppress viral load to undetectable levels. (Undetectable = Untransmittable / U=U).

  • Pre-Exposure Prophylaxis (PrEP): Medications taken by people without HIV to prevent HIV acquisition. Options include daily oral tenofovir-based medications (such as Truvada or Descovy), long-acting injectable cabotegravir (Apretude) every 2 months, and long-acting injectable lenacapavir (Yeztugo) every 6 months.

  • Post-Exposure Prophylaxis (PEP): Emergency 28-day ART regimen started within 72 hours of potential HIV exposure.

Hepatitis B Virus (HBV)
 

• Overview: A viral liver infection transmitted through blood, semen, and other body fluids. Can cause acute illness or chronic liver disease.

• Key Symptoms: Fatigue, dark urine, abdominal pain, loss of appetite, joint pain, and jaundice (yellowing of skin/eyes).

• Management & Prevention:

  • Acute Treatment: Supportive care.

  • Chronic Treatment: Oral antiviral suppressive therapy (Tenofovir, Entecavir) to prevent cirrhosis and liver cancer.

  • Prevention: Safe and effective multi-dose Hepatitis B vaccine.

Diagnostics
 

• Nucleic Acid Amplification Tests (NAAT): High-sensitivity urine tests or vaginal/urethral/rectal/pharyngeal swabs used to detect Chlamydia, Gonorrhea, Trichomonas, and Mycoplasma.

• Serology (Blood Tests):

  • Syphilis: Treponemal (TP-PA, CIA) and non-treponemal (RPR, VDRL) antibody tests.

  • HIV: 4th-generation Antigen/Antibody combination immunoassay.

  • Hepatitis B 

• Viral PCR: Direct swab of active genital lesions to type HSV-1 vs. HSV-2.

Management & Prevention
 

• Barrier Protection: Consistent and correct use of latex or polyurethane condoms and dental dams significantly reduces the transmission of fluid-borne and skin-to-skin STIs.

• Presumptive Partner Treatment (Expedited Partner Therapy / EPT): Providing prescriptions or medications to the sexual partners of patients diagnosed with Chlamydia or Gonorrhea without prior medical examination, preventing re-infection.

• Abstinence During Treatment: Patients and partners must abstain from sexual activity for 7 days following single-dose therapy or until the completion of a multi-day antibiotic regimen and resolution of symptoms.

• Vaccination: Completing recommended vaccination series for HPV and Hepatitis B.

Red Flag Symptoms (When to Seek Urgent Medical Care)
 

• Severe, worsening lower abdominal or pelvic pain (a primary warning sign of Pelvic Inflammatory Disease / PID).

• High fever, chills, or severe systemic weakness accompanying genital symptoms.

• Severe testicular pain, swelling, or tenderness in men.

• Sudden, severe joint pain, swelling, and fever accompanying skin rash or genital discharge (suspected Disseminated Gonococcal Infection).

• Sudden vision changes, eye pain, severe headache, or confusion (warning signs of Neurosyphilis or Ocular Syphilis).
  
   

•                                                          References & Guidelines
   

• Centers for Disease Control and Prevention (CDC). Sexually Transmitted Infections Treatment Guidelines.
  Centers for Disease Control and Prevention (CDC). Chlamydial Infections; Gonococcal Infections; Syphilis; Genital Herpes; Trichomoniasis; HPV Infection.
  Centers for Disease Control and Prevention (CDC). Preexposure Prophylaxis for the Prevention of HIV Infection in the United States.
  Centers for Disease Control and Prevention (CDC). Clinical Recommendation for Injectable Lenacapavir as HIV Preexposure Prophylaxis — United States, 2025.
  Centers for Disease Control and Prevention (CDC). HPV Vaccine Recommendations.