48.2 Sexually Transmitted Infections: Diagnosis, Staging & CDC Guidelines

Neisseria gonorrhoeae: Clinical Staging, Diagnosis & Updated CDC Guidelines

Neisseria gonorrhoeae is a fastidious, Gram-negative, intracellular coffee-bean-shaped diplococcus that infects mucosal columnar and transitional epithelium. Widespread emergence of multidrug-resistant strains has made gonococcal infection a premier public health concern, driving major updates in CDC treatment guidelines.

Clinical Manifestations

• Urogenital Infection:
  • Men: Acute anterior urethritis characterized by copious, frankly purulent, yellow-green urethral discharge and severe burning dysuria. Incubation is 1 to 14 days. Over 90% of men are highly symptomatic, prompting rapid medical attention. Untreated infection can ascend to cause acute epididymo-orchitis or seminal vesiculitis.
  • Women: Endocervical infection is the primary site, but up to 50% to 70% of women are asymptomatic or experience mild non-specific symptoms (mucopurulent cervical discharge, intermenstrual vaginal bleeding, dyspareunia, dysuria). Ascending infection produces acute Pelvic Inflammatory Disease (PID), tubal scarring, ectopic pregnancy, and involuntary infertility.
• Extragenital Infections:
  • Anorectal Gonorrhea: Frequently asymptomatic; may present with proctitis, rectal tenesmus, purulent discharge, rectal bleeding, and pruritus ani.
  • Pharyngeal Gonorrhea: Acquired via receptive oral sex. Overwhelmingly asymptomatic (>90%), creating a massive silent anatomic reservoir for transmission. Highly resistant to eradication.
  • Gonococcal Conjunctivitis: Marked conjunctival injection and copious purulent ocular drainage. In neonates (ophthalmia neonatorum), acquired during delivery through an infected birth canal; can rapidly cause corneal ulceration and permanent blindness.
• Disseminated Gonococcal Infection (DGI): Occurs in 0.5% to 3% of patients via hematogenous spread from mucosal sites, classically in patients with terminal complement deficiencies (C5-C9). Presents as:
  1. Tenosynovitis-Dermatitis-Polyarthralgia Syndrome: Triad of migratory polyarthralgias, acute tenosynovitis (wrist, fingers, ankles), and painless pustular, petechial, or necrotic skin lesions with an erythematous halo concentrated on the distal extremities.
  2. Purulent Septic Arthritis: Acute monoarthritis or oligoarthritis (predominantly knee, wrist, or ankle) with large purulent synovial effusions.

Diagnostic Testing Protocols for Gonorrhea

• Nucleic Acid Amplification Testing (NAAT): The undisputed gold standard for diagnostic sensitivity (>95%) and specificity (>99%).
  • Men: First-catch urine (first 20-30 mL of the urinary stream, without prior cleaning of the meatus; patient should not have voided for at least 1-2 hours) or intraurethral swab.
  • Women: Patient-collected or clinician-collected vaginal swab is the preferred specimen, possessing superior sensitivity to endocervical swabs and urine testing.
  • Extragenital NAAT Testing: Mandatory rectal and pharyngeal swab NAAT for any individual reporting receptive anal or oral sexual exposure within the preceding 12 months. Routine urogenital testing misses up to 70% of extragenital gonococcal infections!
• Gram Stain Microscopy: High sensitivity (>95%) in symptomatic men displaying Gram-negative intracellular diplococci within polymorphonuclear leukocytes. However, Gram stain of endocervical swabs has unacceptably low sensitivity (<40-50%) in women due to normal commensal vaginal flora and cannot exclude infection.
• Bacterial Culture: Performed on selective media (modified Thayer-Martin). Indicated when treatment failure is suspected, enabling phenotypic antimicrobial susceptibility testing.

Updated CDC Antimicrobial Treatment Guidelines

                  CDC GUIDELINES: NEISSERIA GONORRHOEAE TREATMENT

   Clinical Scenario           Patient Body Weight        First-Line Antimicrobial Regimen
   ════════════════════════════════════════════════════════════════════════════════════════════════
   Uncomplicated Urogenital,   < 150 kg (330 lbs)         Ceftriaxone 500 mg IM in a single dose
   Anorectal, or Pharyngeal    ────────────────────────────────────────────────────────────────────
   Gonococcal Infection        >= 150 kg (330 lbs)        Ceftriaxone 1,000 mg (1 g) IM in a single dose

   Co-Infection Status:        If Chlamydia trachomatis has NOT been definitively excluded:
                               ADD Doxycycline 100 mg PO BID x 7 days
                               (If chlamydia is excluded by NAAT, Ceftriaxone monotherapy is sufficient)

   Severe Cephalosporin        Any Weight                 Gentamicin 240 mg IM single dose
   Anaphylaxis / Allergy                                  PLUS Azithromycin 2 g PO in a single dose
   ════════════════════════════════════════════════════════════════════════════════════════════════

[!IMPORTANT] THE PARADIGM SHIFT: AZITHROMYCIN IS NO LONGER RECOMMENDED Under prior CDC guidelines, gonorrhea was routinely treated with "dual therapy" consisting of ceftriaxone plus oral azithromycin 1 g. Dual therapy with azithromycin is NO LONGER RECOMMENDED.

The CDC removed azithromycin due to rapid worldwide escalation of macrolide resistance in N. gonorrhoeae and to preserve macrolide utility for other respiratory and systemic infections. Today, the standard is high-dose intramuscular Ceftriaxone monotherapy (500 mg IM), provided concurrent chlamydial infection has been ruled out.

Chlamydia trachomatis: Pathophysiology & Management

Chlamydia trachomatis is an obligate intracellular bacterium that exists in two distinct cellular forms: the infectious, metabolically inert elementary body (EB) that survives extracellularly, and the non-infectious, metabolically active reticulate body (RB) that replicates within host cell cytoplasmic inclusions.

Serovars & Clinical Spectrum

• Serovars D through K: Cause urogenital chlamydial infections, inclusion conjunctivitis, and neonatal pneumonia.
• Serovars L1, L2, L3: Cause Lymphogranuloma Venereum (LGV), an invasive STI presenting with a transient painless genital papule/ulcer followed by aggressive painful inguinal lymphadenitis ("groove sign" separating inguinal and femoral nodes by Poupart's ligament) and severe hemorrhagic proctitis in men who have sex with men (MSM). LGV requires extended oral Doxycycline 100 mg BID for a full 21 days.

Clinical Presentation & Long-Term Sequelae

• The "Silent" Epidemic: Chlamydia is the most frequently reported bacterial infectious disease in the United States. Over 70% to 80% of infected women and 50% of infected men are entirely asymptomatic.
• When symptomatic, it produces mild dysuria, scant clear or mucoid urethral discharge, or cervical friability with postcoital spotting.
• Long-Term Female Complications:
  • Pelvic Inflammatory Disease (PID): Subclinical or overt ascending infection of the endometrium, fallopian tubes, and ovaries.
  • Tubal Factor Infertility & Ectopic Pregnancy: Each episode of PID increases the risk of irreversible tubal occlusion and subsequent ectopic gestation exponentially (approximate 8% risk after 1 episode, 20% after 2, and >40% after 3 episodes).
  • Fitz-Hugh-Curtis Syndrome (Perihepatitis): Transperitoneal or hematogenous spread causing inflammation of the hepatic capsule. Characterized by severe pleuritic right upper quadrant pain, elevated serum transaminases, and laparoscopically pathognomonic "violin-string" fibrous adhesions between the liver surface and anterior abdominal wall.
• Reactive Arthritis: HLA-B27-associated post-infectious triad of urethritis, uveitis/conjunctivitis, and asymmetric oligoarthritis ("can't see, can't pee, can't climb a tree"), frequently accompanied by circinate balanitis and keratoderma blennorrhagica.

First-Line Antimicrobial Therapy

                  CDC GUIDELINES: CHLAMYDIA TRACHOMATIS REGIMENS

   Patient Category            First-Line Guideline Regimen            Alternative Regimen
   ══════════════════════════════════════════════════════════════════════════════════════════════
   Non-Pregnant Adults         Doxycycline 100 mg PO BID x 7 days      Azithromycin 1 g PO single dose
   and Adolescents             (Gold Standard First-Line)              OR Levofloxacin 500 mg PO daily x 7d

   Pregnant Patients           Azithromycin 1 g PO in a single dose    Amoxicillin 500 mg PO TID x 7 days
                               (Doxycycline CONTRAINDICATED)
   ══════════════════════════════════════════════════════════════════════════════════════════════

• Why Doxycycline Surpassed Azithromycin: Randomized clinical trials demonstrated that oral Doxycycline achieves a >95% to 98% cure rate for urogenital and anorectal chlamydia. Single-dose Azithromycin achieves comparable cure rates (>95%) for urogenital infections but is substantially inferior for rectal chlamydial infection (microbiologic cure rate only 70% to 80%). Because asymptomatic rectal co-infection is common across all demographics, Doxycycline 100 mg BID for 7 days is the definitive first-line standard.
• Test of Cure (TOC): Routine TOC is NOT recommended for non-pregnant patients treated with first-line regimens unless compliance is questionable, symptoms persist, or reinfection is suspected. However, TOC is MANDATORY in pregnancy (perform NAAT 4 weeks after completing treatment).
• Re-screening Mandate: All patients treated for chlamydia (or gonorrhea) must be rescreened 3 months post-treatment due to high rates of reinfection from untreated partners.

Syphilis: Treponema pallidum Staging, Clinical Manifestations & Neurosyphilis

Syphilis is a chronic systemic infection caused by the spirochete Treponema pallidum subspecies pallidum. Because it can mimic almost any clinical pathology, it is historically known as "The Great Imitator."

Clinical Staging & Manifestations

                    CLINICAL STAGING OF TREPONEMA PALLIDUM

   Clinical Stage             Incubation & Timing         Cardinal Clinical Features
   ═══════════════════════════════════════════════════════════════════════════════════════════════════
   Primary Syphilis           10 to 90 days               Solitary, painless chancre with an indurated
                              (average 21 days)           base and clean, non-purulent crater; bilateral
                                                          painless regional lymphadenopathy; heals in 3-6 weeks

   Secondary Syphilis         2 to 8 weeks after          Disseminated bacteremic phase: diffuse non-pruritic
                              chancre resolution          maculopapular rash involving the PALMS and SOLES;
                              (up to 6 months)            condylomata lata (moist verrucous plaques in perineum);
                                                          mucous patches; epitrochlear lymphadenopathy; fever

   Early Latent Syphilis      Infection acquired within   Completely asymptomatic; seroreactive non-treponemal
                              preceding 12 months         and treponemal tests; potentially infectious

   Late Latent Syphilis       Infection acquired >=12 mo  Completely asymptomatic; seroreactive; low infectious
   / Unknown Duration         prior or unknown duration   risk except vertical maternal-fetal transmission

   Tertiary Syphilis          1 to 30+ years after        Granulomatous gummas (skin, bones, liver);
                              initial untreated infection Cardiovascular syphilis (ascending thoracic aortic
                                                          aneurysm, aortic regurgitation, coronary stenosis)
   ═══════════════════════════════════════════════════════════════════════════════════════════════════

Primary Syphilis

• The hallmark lesion is the chancre: an ulcer that begins as a single painless papule that rapidly erodes into a clean-based, punched-out crater with raised, cartilaginous, indurated borders.
• Painless bilateral inguinal lymphadenopathy accompanies the chancre.
• The chancre heals spontaneously within 3 to 6 weeks without scarring, often giving the patient false reassurance that the disease has resolved.

Secondary Syphilis

• Manifests secondary to widespread vascular dissemination of spirochetes throughout tissues.
• Cutaneous Eruption: Bilateral, symmetric, non-pruritic copper-red or pink maculopapular eruption. Crucially involves the palms of the hands and soles of the feet (a key board-exam differentiator alongside erythema multiforme, Rocky Mountain spotted fever, and Coxsackievirus A16).
• Condylomata Lata: Highly infectious, hypertrophic, flat, moist, broad-based verrucous plaques that flourish in warm, intertriginous skin folds (perineum, vulva, scrotum, perianal region). (Do not confuse with HPV condylomata acuminata, which are dry, pedunculated, cauliflowered warts).
• Mucous Patches: Superficial, painless, grayish-white silvery erosions on the buccal mucosa, tongue, or lips, teeming with spirochetes.
• Lymphadenopathy: Generalized non-tender lymphadenopathy. Palpable epitrochlear lymphadenopathy is highly specific for secondary syphilis.

Neurosyphilis, Ocular Syphilis & Otosyphilis

[!CAUTION] NEUROSYPHILIS CAN OCCUR AT ANY CLINICAL STAGE Central nervous system invasion by Treponema pallidum can occur within days of initial primary infection and does NOT require decades to manifest.

• Early Neurosyphilis: Manifests months to years after infection as acute syphilitic meningitis (cranial nerve palsies, particularly CN VII and VIII) or meningovascular syphilis (ischemic stroke syndrome in a young individual caused by endarteritis of middle cerebral artery branches).
• Late Neurosyphilis: Manifests decades later:
  • Tabes Dorsalis: Slow progressive demyelination and degeneration of the spinal cord posterior columns and dorsal roots. Clinical tetrad: sensory ataxia (positive Romberg test, stomping wide-based gait), loss of proprioception and vibratory sensation, "lightning" lancinating pains in the lower extremities, and neurogenic Charcot joints.
  • General Paresis: Chronic progressive dementia, personality disintegration, grandiose delusions, tremors, and dysarthria.
  • Argyll Robertson Pupil: Pathognomonic bilateral small, irregular pupils that exhibit light-near dissociation: pupils briskly constrict during visual accommodation for near objects, but DO NOT react to direct light stimulation ("Prostitute's Pupil: Accommodates but does not React").
• Ocular and Otic Syphilis: Posterior uveitis, panuveitis, optic neuropathy, sensorineural hearing loss, and vestibular vertigo. Any syphilitic patient with ocular or auditory symptoms must be staged and managed identically to neurosyphilis!

Diagnostic Algorithms & CDC Staging Treatment

Serodiagnosis requires two distinct classes of tests: non-treponemal and treponemal.

                  SEROLOGIC TESTING COMPARISON FOR SYPHILIS

   Test Category          Specific Assays                 Clinical Role & Interpretation
   ═════════════════════════════════════════════════════════════════════════════════════════════════
   Non-Treponemal Tests   RPR (Rapid Plasma Reagin)       Detects antibodies to cardiolipin-cholesterol-
                          VDRL (Venereal Disease          lecithin antigens. QUANTITATIVE titer reflects
                          Research Laboratory)            disease activity and monitors treatment success.
                                                          Becomes non-reactive or serofast with time.

   Treponemal Tests       TP-PA (T. pallidum Particle)    Detects specific antibodies directed against
                          FTA-ABS (Fluorescent Absorbed)  Treponema pallidum antigens. QUALITATIVE only.
                          EIA / CIA (Enzyme Immunoassay)  Remains POSITIVE FOR LIFE (cannot monitor cure).
   ═════════════════════════════════════════════════════════════════════════════════════════════════

Traditional vs. Reverse Sequence Algorithms

• Traditional Algorithm: Screen with a quantitative non-treponemal test (RPR). If non-reactive, report negative. If reactive, confirm specificity with a treponemal assay (TP-PA). If both are reactive, syphilis is diagnosed.
• Reverse Sequence Algorithm: Increasingly adopted by modern automated clinical laboratories. Initial screening begins with an automated treponemal test (EIA or CIA):
  • If EIA/CIA is reactive, the laboratory reflexively tests the sample with a quantitative non-treponemal test (RPR):
    • If RPR is reactive: Confirms active untreated syphilis (or recently treated infection with residual titer).
    • If RPR is non-reactive (discordant): Perform a second, distinct treponemal assay (TP-PA):
      • If second treponemal test (TP-PA) is reactive: Represents either previously successfully treated syphilis or untreated late latent syphilis.
      • If second treponemal test (TP-PA) is non-reactive: The initial screening EIA was a biological false positive.

Monitoring Treatment Success: The Fourfold Titer Drop

Non-treponemal titers (RPR or VDRL) are used to document curative response:

• A fourfold decline in titer (equivalent to a two-dilution drop) confirms adequate therapeutic response.
  • Example: A pre-treatment RPR of 1:32 dropping to 1:8 (or 1:64 dropping to 1:16) represents a fourfold decline.
• Titers should be followed at 6 and 12 months post-treatment in primary/secondary syphilis, and at 6, 12, and 24 months in latent syphilis.

CDC Guideline Antimicrobial Regimens

                  CDC GUIDELINES: SYPHILIS TREATMENT REGIMENS

   Syphilis Clinical Stage                 First-Line Recommended Antimicrobial Regimen
   ═══════════════════════════════════════════════════════════════════════════════════════════════════
   Primary, Secondary, or                  Benzathine Penicillin G 2.4 million units IM in a
   Early Latent Syphilis (< 1 year)        SINGLE DOSE (Administered as 1.2 million units in each buttock)

   Late Latent, Latent of Unknown          Benzathine Penicillin G 2.4 million units IM
   Duration, or Tertiary Syphilis          ONCE WEEKLY FOR 3 CONSECUTIVE WEEKS (Total 7.2 million units)

   Neurosyphilis, Ocular Syphilis,         Aqueous Crystalline Penicillin G 18 to 24 million units IV
   or Otic Syphilis                        daily, administered as 3 to 4 million units IV every 4 hours
                                           (or continuous IV infusion) for 10 to 14 DAYS
   ═══════════════════════════════════════════════════════════════════════════════════════════════════

[!CAUTION] CRITICAL PREGNANCY MANDATE: PENICILLIN IS THE ONLY ACCEPTABLE DRUG In pregnant patients, Parenteral Benzathine Penicillin G is the ONLY curative treatment that reliably prevents maternal-fetal spirochetal transmission and congenital syphilis.

Doxycycline and tetracyclines are strictly contraindicated in pregnancy due to permanent fetal tooth discoloration and bone growth inhibition. Erythromycin and azithromycin do NOT cross the placental barrier in sufficient concentrations to treat the fetus. Therefore, any pregnant woman with syphilis and a documented true penicillin allergy MUST BE ADMITTED FOR INPATIENT PENICILLIN DESENSITIZATION followed immediately by the appropriate Benzathine Penicillin G regimen.

The Jarisch-Herxheimer Reaction & Expedited Partner Therapy

The Jarisch-Herxheimer Reaction

• Pathophysiology: An acute, systemic inflammatory reaction provoked by the rapid bactericidal destruction and lysis of massive numbers of spirochetes upon initiating penicillin therapy. Lysis releases large quantities of treponemal endotoxin-like outer membrane lipoproteins into the circulation, stimulating macrophages to release a surge of pro-inflammatory cytokines: Tumor Necrosis Factor-alpha (TNF-alpha), Interleukin-6 (IL-6), and Interleukin-8 (IL-8).
• Incidence & Timing: Most commonly observed in patients with high bacterial burdens (seen in 50% to 75% of patients treated for secondary syphilis, 30% with primary syphilis). Symptoms begin abruptly within 2 to 24 hours following the first penicillin injection.
• Clinical Manifestations: Shaking chills, high fevers, diaphoresis, headache, generalized myalgias, tachycardia, transient hypotension, and a transient accentuation and erythema of the syphilitic skin rash.
• Clinical Management & Distinction from Penicillin Allergy:
  • The Jarisch-Herxheimer reaction is benign and self-limiting, resolving spontaneously within 12 to 24 hours.
  • Management is purely supportive: antipyretics (acetaminophen 650-1000 mg PO every 6 hours or ibuprofen 600 mg PO every 8 hours), oral or intravenous hydration, and bed rest.
  • CRITICAL DISTINCTION: It is NOT an IgE-mediated penicillin allergy (no urticarial wheals, bronchospasm, angioedema, or anaphylaxis). Penicillin therapy MUST NOT be discontinued, and the patient should NOT be labeled as penicillin-allergic.
  • Pregnancy Warning: In pregnant women, the intense cytokine surge can induce transient uterine contractions, non-reassuring fetal heart rate decelerations, or preterm labor; pregnant women with secondary syphilis should be monitored in a setting equipped for fetal monitoring.

Expedited Partner Therapy (EPT)

Expedited Partner Therapy (EPT) is the evidence-based clinical practice of treating the sexual partners of patients diagnosed with an STI by providing prescriptions or medications directly to the index patient to deliver to their partners, without requiring the healthcare provider to examine the partner first.

• Epidemiologic Rationale: Reinfection rates from untreated baseline partners reach 20% to 30% within 3 months. Traditional partner notification (advising patients to tell partners to seek care) fails in >50% of cases.
• Legal Standing & Practice: EPT is legally permissible in almost all 50 US states for heterosexually transmitted Chlamydia trachomatis and Neisseria gonorrhoeae.
  • For chlamydia: Index patient is provided an extra prescription for oral Doxycycline 100 mg BID for 7 days (or oral Azithromycin 1 g single dose if adherence is questionable) accompanied by educational brochures warning of allergy, pregnancy, and instructing sexual abstinence until 7 days post-treatment.
  • For gonorrhea: EPT is more complex because first-line therapy requires intramuscular ceftriaxone. If an in-person partner clinic visit cannot be achieved, CDC guidelines permit oral Cefixime 800 mg PO in a single dose delivered to the partner via EPT.
• Lookback Interval: All sexual contacts within the preceding 60 days must be evaluated and treated.