Chlamydia is a bacterial infection, caused by Chlamydia trachomatis. It is the most common bacterial sexually transmitted infection (STI) worldwide, occurring most frequently among young sexually active adults. Chlamydia is spread by having unprotected vaginal, anal, or oral sex with someone who has chlamydia, or from mother-to-child during childbirth.

Approximately 70% of women and 50% of men do not show any symptoms from genital infections due to chlamydia. C. trachomatis causes cervicitis in women and urethritis in men, as well as extra-genital infections, including rectal and oropharyngeal infections. Untreated chlamydial infection may cause severe complications in the upper reproductive tract, primarily in young women, including ectopic pregnancy, inflammation of the fallopian tubes and infertility. Maternal infection is associated with serious adverse outcomes in neonates, such as preterm birth, low birth weight, eye infection, nasopharyngeal infection and pneumonia. Chlamydia diagnosis is usually based on laboratory tests and uses urine samples or swabs samples. Uncomplicated Chlamydia can be easily cured with antibiotics and is usually resolved within days or weeks.

Lymphogranuloma venereum (LVG), a genital ulcer disease (GUD) that affects lymphoid tissue is caused by a more invasive strain (serovar) of Chlamydia trachomatis, and it is increasingly prevalent among men who have sex with men (MSM) in some settings.

The World Health Organization (WHO) estimates that in 2012, 131 million new cases of chlamydia infections happened among adults and youth aged 15–49 years worldwide, with around 128 million cases already present. The highest number of cases are found in WHO Region of the Americas and the WHO Western Pacific Region.

Key Facts

  • In 2012, there were 17.8 million new cases of chlamydia among females, and 7 million new cases among men in the Region of the Americas
  • In 2012, there were 18.8 million existing cases of chlamydia among females, and 4.5 million existing cases among men in the Region of the Americas
  • In many countries, the number of chlamydia is highest among girls aged 15–19 years, followed by young women aged 20-24 years

PAHO/WHO response

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