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Chlamydia Infection (Sexually Transmitted)

Basics

  • Causative organism: Chlamydia trachomatis, intracellular bacterium with biphasic life cycle.
  • Transmission: vaginal, anal, oral sex; vertical during vaginal delivery.
  • Mostly asymptomatic, especially in females.
  • Untreated: PID, ectopic pregnancy, infertility.
  • Systems affected: reproductive.

Epidemiology

  • 1.64 million cases reported in 2020 in the US.
  • Highest prevalence in females aged 20-24 years.
  • Females > males likely due to increased testing.
  • Estimated 2% of young sexually active individuals affected.
  • nvCT variant reported in Nordic countries, causes false-negative tests.

Etiology & Pathophysiology

  • Serotypes D-K cause genital infections.
  • EB (elementary body): infectious, metabolically inactive form.
  • RB (reticulate body): intracellular, metabolically active form.
  • Infection invades columnar epithelium, avoids lysosomal degradation.

Risk Factors

  • Multiple or concurrent sexual partners.
  • No barrier contraception.
  • Ethnicity: Black, Hispanic, Native American, Alaska Native.
  • MSM at increased risk for rectal/pharyngeal infections.

Prevention

  • Annual screening for sexually active women ≤25 years.
  • Rescreen positive cases at ~3 months post-treatment.
  • Screen high-risk MSM annually at genital and extragenital sites.
  • NAAT is preferred test except in prepubescent girls or child sexual abuse cases.
  • Emerging use of doxycycline postexposure prophylaxis (Doxy-PEP) in MSM and transgender women.

Associated Conditions

  • Female anatomy: PID (~10%), infertility, ectopic pregnancy, chronic pelvic pain.
  • Male anatomy: epididymitis, nongonococcal urethritis, Reiter syndrome, proctitis.
  • Neonates: inclusion conjunctivitis, otitis media, pneumonia.
  • Other Chlamydia species cause LGV (L1-L3) and trachoma (A-C).

Diagnosis

  • History: sexual practices, partners, prior STIs.
  • Female symptoms: mucopurulent discharge, dysuria, pelvic pain.
  • Male symptoms: dysuria, urethral discharge, scrotal pain.
  • Physical exam: genital inspection, lymphadenopathy, cervical motion tenderness.
  • NAAT testing: >95% sensitivity, >99% specificity; urine, vaginal swabs.
  • Screen for coinfections (gonorrhea, HIV, syphilis).
  • Repeat testing recommended in pregnancy and for reinfection monitoring.

Treatment

General

  • Concurrent testing/treatment for gonorrhea, HIV, syphilis.
  • Treat sexual partners from past 60 days or most recent.

First-line

  • Doxycycline 100 mg PO BID for 7 days (preferred).
  • Alternatives: azithromycin 1 g PO single dose, levofloxacin 500 mg PO daily for 7 days.
  • PID: ceftriaxone IM 250 mg + doxycycline 100 mg PO for 14 days ± metronidazole.
  • Doxy-PEP: 200 mg doxycycline ASAP post condomless sex (within 3 days) in MSM/transgender women.

Pregnancy

  • Avoid tetracyclines, quinolones.
  • Azithromycin 1 g PO single dose or
  • Amoxicillin 500 mg PO TID for 7 days or
  • Erythromycin base 500 mg PO QID for 7 days.

Second-line

  • Erythromycin base/ethylsuccinate, levofloxacin, ofloxacin as alternatives.

Additional

  • Patient-delivered partner therapy (PDPT) or expedited partner therapy (EPT) to reduce reinfection.

Follow-Up

  • Abstain from sexual activity until treatment complete (7 days or full course).
  • Test of cure not routinely required except in pregnancy (3-4 weeks post-treatment).
  • Rescreen for reinfection at 3 months.
  • Repeat 3rd trimester screening in high-risk pregnancy.

Prognosis

  • Good with treatment.
  • Chlamydia enhances HIV transmission risk.
  • Female infertility and ectopic pregnancy risks without treatment.
  • Male complications include rare urethral stricture.

Clinical Pearls

  • Annual chlamydia screening recommended in sexually active women ≤25 years.
  • Treat patients and partners concurrently to prevent reinfection.
  • Doxycycline is most effective for rectal infections.
  • Use caution with azithromycin in patients with QT prolongation or electrolyte abnormalities.
  • Doxy-PEP shows promise in high-risk MSM populations.