Chlamydia Infection (Sexually Transmitted)

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  • Chlamydia trachomatis is an intracellular membrane-bound prokaryotic organism. Chlamydia derives from the Greek word for “cloak.”
  • Chlamydia is the most common bacterial sexually transmitted infection (STI) in the United States (1)[A].
  • Transmitted through vaginal, anal, or oral sex; transmitted vertically during vaginal delivery
  • Most cases are asymptomatic, especially in females. Untreated disease can lead to pelvic inflammatory disease (PID), ectopic pregnancy, and infertility.
  • System(s) affected: reproductive

Pregnancy Considerations
Perinatal acquisition may result in neonatal pneumonia and/or conjunctivitis.


  • Mandatory reporting started in 1985; there has generally been a steady increase in incidence since.
  • ~1.6 million reported cases in 2016. Increasing incidence reflects broader screening, improved testing, and better reporting (rather than a large increase in disease burden) (1).
  • Swedish new variant of C. trachomatis (nvCT) first reported in 2006; often produces false-negative tests; largely confined to Nordic countries

  • 497/100,000 people in the United States in 2016 (1)
  • Young females, ethnic minorities most affected
  • Highest prevalence ages 20 to 24 years
  • Predominant sex: females > males. Females have 2 times higher reported incidence and prevalence than males. This likely reflects increased testing in females. Increasing use of highly sensitive nucleic acid amplification test (NAAT) urine screening may increase identification in males.
  • Infection rates ~6 times higher in blacks than whites. Rates are higher in larger urban areas.
  • Highest male prevalence in heterosexual adolescents
  • Estimated to affect ~2% of young sexually active individuals in the United States

Etiology and Pathophysiology

C. trachomatis serotypes D to K associated with genital tract infections. Chlamydia is an obligate intracellular organism. Chlamydia has biphasic life cycle. Exists extracellularly as elementary body (EB) that is metabolically inactive and infectious. Once taken up by host cell (typically columnar epithelium of the genital tract), the EB prevents lysosomal phagocytosis and transforms to reticulate body (RB) which requires energy from host cell to synthesize RNA, DNA, and proteins. After taking up host cell residence, EB are released and are capable of infecting neighboring cells or spreading the infection through sexual contact.

Risk Factors

Risk correlates with:

  • Number of lifetime sexual partners and number of concurrent sexual partners
  • No use of barrier contraception during intercourse
  • Black/Hispanic/Native American and Alaskan Native ethnicity
  • Men who have sex with men (MSM) may be at higher risk for rectal and pharyngeal chlamydia than other groups; consider testing with NAAT when appropriate (2)[B].

General Prevention

  • Screen populations with prevalence >5% at least annually (1)[A].
  • Screening recommended if new or >1 sex partner in past 6 months; attending an adolescent clinic, family planning clinic, STD or abortion clinic, or attending a jail or other detention center clinic. Screen if rectal pain, discharge or tenesmus, testicular pain; test all individuals with urethral or cervical discharge.
  • All sexually active women ≤25 years of age should be screened at least yearly. Repeat testing in ~3 months is recommended for those who screen positive because reinfection rate is high regardless of whether the sexual partner is treated (3)[A].
  • Consider screening sexually active men ≤25 years of age particularly in high-risk populations.
  • Screen high-risk MSM annually with genital and extragenital screening (4)[A].
  • NAAT is the preferred screening test in all circumstances except child sexual abuse involving boys or rectal/oropharyngeal testing in prepubescent girls. For these situations, culture and susceptibility testing is preferred (4)[A].
  • Acceptable to screen women for chlamydia on same day as intrauterine device (IUD) insertion—treat if positive (no need to remove IUD in this circumstance) (5)[B]

Commonly Associated Conditions

  • Females
    • PID: ~10% develop PID within 12 months if untreated.
    • Infertility, ectopic pregnancy
    • Chronic pelvic pain
    • Urethral syndrome (dysuria, frequency, and pyuria in the absence of infection)
    • Arthritis (less common)
    • Spontaneous abortion
  • Males
    • Epididymitis and nongonococcal urethritis
    • Reiter syndrome (HLA-B27)
    • Proctitis
  • Neonates
    • Inclusion conjunctivitis (occurs in ~40% of exposed neonates)
    • Otitis media
    • Pneumonia
    • Pharyngitis
  • Diseases caused by other chlamydial species
    • Lymphogranuloma venereum (LGV): C. trachomatis serotypes L1 to L3
    • Trachoma: C. trachomatis serotypes A to C

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