Sexually Transmitted Infections

1. THE 2-MINUTE PHYSIOLOGY (Rapid Pathophysiology)

• The Barrier Breach: Sexually transmitted infections (STIs) are caused by pathogens that spread through direct contact with the penis, vagina, mouth, or anus, requiring a disrupted epithelial barrier or mucous membrane for inoculation.
• Intracellular and Systemic Invasion: Certain pathogens, like Chlamydia trachomatis (an obligate intracellular organism), replicate within mucosal cells, triggering localized inflammation. Others, such as the spirochete Treponema pallidum (syphilis) and Neisseria gonorrhoeae, can rapidly disseminate via the lymphatic system and bloodstream, leading to systemic, life-threatening complications like neurosyphilis or disseminated gonococcal infection (DGI).
• The Cofactor Effect: The presence of ulcerating STIs (e.g., herpes, syphilis, chancroid) causes a mechanical breakdown of the mucosal barrier and recruits immune cells to the site, acting as a profound cofactor that significantly increases the risk of human immunodeficiency virus (HIV) transmission and acquisition.

2. THE BEDSIDE ACTION PLAN (Rapid ER Management)

• Empirical Resuscitation: In the ED, do not wait for confirmatory laboratory results to initiate treatment in symptomatic, high-risk patients. Single-dose directly observed therapy in the ED is the gold standard to ensure compliance.
• The First-Line Pharmacotherapy (Uncomplicated GC/Chlamydia):
• Administer Ceftriaxone 500 mg IM in a single dose (increase to 1,000 mg IM if the patient weighs >150 kg).
• PLUS Doxycycline 100 mg PO BID for 7 days (Substitute with Azithromycin 1 g PO single dose if the patient is pregnant).
• If applicable, add Metronidazole 500 mg PO BID for 7 days (for women, to cover Trichomonas and anaerobes).
• The Sexual Assault Protocol: For adult survivors, treat empirically for STIs (using the regimen above). Administer emergency contraception (e.g., Ulipristal or Levonorgestrel) within 72–120 hours. Assess the need for HIV post-exposure prophylaxis (PEP) using a 28-day regimen (e.g., bictegravir OR tenofovir/emtricitabine + raltegravir) ideally within 72 hours. Administer hepatitis B immune globulin (HBIG) and/or vaccine if unvaccinated, and update tetanus.
• Syphilis and HSV: Treat primary or secondary syphilis with Benzathine penicillin G 2.4 million units IM. For primary genital herpes (HSV), initiate systemic antivirals (e.g., oral acyclovir, valacyclovir) within 72 hours of symptom onset.

3. THE DIAGNOSTIC GRID (Differential Diagnosis & Workup)

• Critical "Can't-Miss" Mimics:
• Ectopic pregnancy
• Ovarian or testicular torsion
• Acute appendicitis
• Tubo-ovarian abscess (TOA).
• Prioritized Diagnostic Workup:
• Pregnancy Test: Mandatory for all women of childbearing age; impacts both the differential diagnosis and antibiotic selection.
• NAAT (Nucleic Acid Amplification Test): The gold standard for C. trachomatis and N. gonorrhoeae.
• Serology: Screen for HIV, Hepatitis B/C, and Syphilis (using non-treponemal screening like RPR/VDRL, followed by treponemal confirmatory testing).
• Blood Cultures: Must be drawn prior to antibiotic administration if Disseminated Gonococcal Infection (DGI) is suspected due to rising antimicrobial resistance.

4. THE VISUAL BOARD (ECG / POCUS / Imaging)

• The Ulcer Visual Checklist:
• Primary Syphilis: A solitary, painless ulcer with indurated margins and a nonexudative base (chancre).
• Chancroid: Extremely painful, punched-out ulcers associated with suppurative inguinal adenitis (buboes).
• Genital Herpes: Painful grouped vesicles surrounded by an erythematous base that ulcerate.
• The Skin Eruption Checklist:
• Secondary Syphilis: A papulosquamous erythematous eruption classically involving the palms and soles, or smooth, broad-based perianal plaques (condyloma lata).
• Disseminated Gonococcemia: Look at the distal extremities (fingers/wrists) for erythematous or hemorrhagic papules that evolve into pustules with an erythematous halo.
• POCUS/Imaging: In female patients presenting with severe, unilateral lower abdominal pain and suspected PID, a pelvic ultrasound (transvaginal) is the gold standard imaging modality to definitively rule out a tubo-ovarian abscess or ectopic pregnancy.

5. THE SCORING MATRIX (Risk Stratification & Guidelines)

• CDC PID Diagnostic Criteria: To prevent the severe sequelae of untreated pelvic inflammatory disease (PID), the threshold for treatment is intentionally low.
• Minimum Criteria (requires only ONE): Cervical motion tenderness ("chandelier sign"), uterine tenderness, OR adnexal tenderness.
• Additional Criteria (increases specificity): Oral temperature >101°F (38.3°C), abnormal mucopurulent discharge, or abundant WBCs on saline microscopy.
• Admission Criteria for STIs/PID:
• Inability to exclude a surgical emergency (e.g., appendicitis).
• Pregnancy.
• Presence of a Tubo-ovarian abscess.
• Severe toxicity (high fever, intractable vomiting) or inability to tolerate oral medications.
• Failure to respond to outpatient therapy.
• Signs of disseminated disease (DGI, septic arthritis) or neurosyphilis.

6. THE DANGER ZONE (Pitfalls & Critical Actions)

• The Sexual Assault Testing Pitfall: Pitfall: Routinely swabbing asymptomatic adult sexual assault victims for STI cultures. Critical Action: Do NOT routinely test asymptomatic adults; instead, empirically treat them for Gonorrhea, Chlamydia, and Trichomonas. A positive test from an adult could reflect prior consensual contact and complicate forensic evidence. (Note: Prepubertal children should be fully tested, as a positive test is legal evidence of abuse, but not empirically treated).
• The Penicillin Allergy Trap in Pregnancy: Pitfall: Prescribing doxycycline to a pregnant patient with primary syphilis because she has a penicillin allergy. Critical Action: Penicillin remains the absolute drug of choice for syphilis in pregnancy; the patient must be admitted for formal penicillin desensitization.
• The Herpes Diagnostic Trap: Pitfall: Relying on a Tzanck smear or purely on visual clinical diagnosis to confirm or rule out HSV. Critical Action: The Tzanck smear is insensitive and nonspecific. Use HSV type-specific NAATs for confirmation. Furthermore, do not prescribe topical antivirals for genital herpes, as they are ineffective.
• Mandatory Reporting: Critical Action: Emergency providers are legally required to report certain notifiable infections to public health departments, including Gonorrhea, Chlamydia, Syphilis, Chancroid, and HIV.

7. MCQ MASTERCLASS (Written Exam Tips)

• Buzzword: "Painless ulcer with indurated margins" = Primary Syphilis.
• Buzzword: "Painful, punched-out ulcers with inguinal buboes" = Chancroid (Haemophilus ducreyi).
• Buzzword: "Migratory asymmetric polyarthralgias with hemorrhagic pustules on the hands/wrists" = Disseminated Gonococcal Infection.
• Buzzword: "Groove sign" (painful femoral/inguinal lymphadenopathy above and below the inguinal ligament) = Lymphogranuloma venereum (LGV).
• Distractor Differentiation: An exam question may offer "Topical Acyclovir" for a patient with painful vesicular genital lesions. Differentiation: This is a distractor. Topical antiviral agents are not effective against genital herpes; oral systemic therapy (e.g., acyclovir, valacyclovir) is required.

8. THE BOARDROOM SCRIPT (OSCE & Oral Board Tips)

• Communication Pearls: "I recognize this is a sensitive topic. I want to assure you that our conversation is entirely confidential. Because many of these infections frequently coexist, I am going to order screening tests for HIV, syphilis, and hepatitis B and C to ensure we aren't missing anything."
• Physical Exam Maneuvers: "I will perform a comprehensive physical exam including a visual inspection of the oral and anogenital mucosa. In female patients, I will perform a bimanual and speculum exam to specifically evaluate for cervical motion tenderness, adnexal masses, or mucopurulent discharge."
• Articulating the Management Plan: "Based on the presence of mucopurulent discharge and lower abdominal pain, my presumptive diagnosis is cervicitis with a high suspicion for PID. I will order a urine pregnancy test, NAATs for Gonorrhea and Chlamydia, and a pelvic ultrasound to rule out a tubo-ovarian abscess. I am initiating empiric treatment with single-dose Ceftriaxone 500 mg IM, plus Doxycycline and Metronidazole. I will strictly advise the patient to ensure her partners are treated before re-engaging in sexual activity."