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Self-Study STD Module - Chlamydia

Epidemiology (continued)

Risk Factors for Chlamydia
  • Adolescent
  • New or multiple sex partners
  • History of STD
  • Presence of another STD
  • Oral contraceptive user
  • Lack of barrier contraception

Risk Factors

Certain risk factors are associated with chlamydial infection. Being an adolescent is a risk factor because adolescents may engage in risky behaviors, such as unprotected sex. The presence of columnar epithelial cells on the ectocervix is called ectopy which is more susceptible to chlamydial infection. Ectopy is more common among adolescents. Oral contraceptive use also contributes to ectopy.

Other risk factors include new or multiple sex partners, history of STD infection, presence of another STD, and lack of barrier contraception.


C. trachomatis is highly transmissible, with chlamydial infection rates in partners reported at >50%. Chlamydia is transmitted through genital sexual contact or through vertical transmission from mother to infant during the perinatal period. Transmission rates are thought to be slightly higher from men to women, but since there is a significant reservoir of asymptomatic carriers in the general population, the exact rate of transmission is unknown. Perinatal transmission results in neonatal conjunctivitis in 30%-50% of exposed babies and pneumonia in 3%-16% of exposed babies.

The incubation period preceding symptomatic infection is 7-21 days. After treatment of chlamydia, re-infection is very common either because the patient’s sex partners were not treated or because the patient had sex with a new partner infected with C. trachomatis.

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Page last modified: March 31, 2010
Page last reviewed: March 31, 2010

Content Source:Division of STD Prevention, National Center for HIV/AIDS, Viral Hepatitis, STD, and TB Prevention

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