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Chlamydial Sexually Transmitted Diseases

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  • An obligate, intracellular membrane-bound prokaryotic organism, C. trachomatis is the most common bacterial STI in the US.
  • Transmitted through vaginal, anal, or oral sex; may also occur vertically from mother to infant during vaginal birth
  • Screening has increased over the past 20 years but remains suboptimal, with annual screening rates of only 41–54% among sexually active females aged 16–25 in 2009 (1).
  • Majority of cases are asymptomatic, especially females. Untreated disease can lead to pelvic inflammatory disease (PID), ectopic pregnancy, infertility.
  • System(s) affected: Reproductive

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


  • Mandatory reporting started in 1985, with data showing steady increase in incidence since.
  • 1.3 million reported cases in 2010. This is the largest number of cases of any disease ever reported to the CDC. Increasing incidence reflects greater screening, improved testing modalities, and better reporting rather than a large increase in disease burden.
  • Swedish new variant Chlamydia (nvCT) was first reported in 2006; often produces false-negative tests; largely confined to Nordic countries (2).
  • 426/100,000 people in the US in 2010
  • Populations most affected: Young females, particularly those of ethnic minority groups
  • Peak incidence: Age 18–20.
  • Predominant sex: Females > Males. Females have >2.5× higher reported incidence and prevalence than males, but this likely reflects increased testing in females. Increasing use of urine screening may increase screening in males.
  • Minorities bear the highest burden, with infection rates among blacks in >8× that of whites. Rates among American Indian/Alaska natives and Hispanics were 4.3× and 2.7× higher than whites, respectively. Rates higher in larger, more metropolitan areas.
  • ~15% of adolescent females entering corrective facilities tested positive.

Risk Factors

Risk correlates with:

  • Number of lifetime sexual partners and number of concurrent sexual partners
  • Lack of barrier contraception during sexual intercourse
  • Younger age (highest in females 15–19 years, males 20–24 years)
  • Black/Hispanic/American Indian and Alaskan native ethnicity

General Prevention

  • Populations with prevalence >5% should be screened at least annually (1). Screen if: New or >1 sex partner in past 6 months, attending an adolescent or family-planning clinic or STD or abortion clinic, attending a jail or other detention-center clinic, rectal pain, discharge or tenesmus, testicular pain; test any individual with urethral or cervical discharge.
  • All sexually active women≤25 years of age should be screened at least yearly, and repeat testing in ∼3 months is recommended for those who screen positive, not as test of cure but because reinfection rate is high regardless of whether the sexual partner is treated (3)[A].
  • Screening sexually active men ≤25 years is controversial but should be strongly considered in high-risk populations.
  • Annual screening is recommended for men who have sex with men; this may include, as appropriate, rectal nucleic acid amplification test (NAAT) and/or urethral (urine) testing.


C. trachomatis serotypes D–K

Commonly Associated Conditions

  • Females:
    • PID: ~10% of women with positive chlamydia screen developed PID within 12 months (4).
    • Infertility and ectopic pregnancies
    • Chronic pelvic pain
    • Mucopurulent cervicitis with cervical edema and propensity to bleed during speculum exam
    • Urethral syndrome (common in women with dysuria, frequency, and pyuria in the absence of infection with uropathogen)
    • Arthritis (rare)
    • Spontaneous abortion (5)
  • Males:
    • Epididymitis and nongonococcal urethritis
    • Reiter syndrome (HLA-B27)
    • Proctitis (men who have sex with men)
  • Neonates:
    • Inclusion conjunctivitis (occurs in ~40% of exposed neonates) (3)
    • Otitis media
    • Pneumonia
    • Pharyngitis
  • Diseases caused by other chlamydial species:
    • Lymphogranuloma venereum: C. trachomatis serotypes L1–L3
    • Trachoma: C. trachomatis serotypes A–C

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