Pronounced: Cla-MID-ee-a

Chlamydia are bacteria, but they are not capable of surviving on their own. Instead, they can grow only inside other living cells, like viruses. Outside living cells chlamydia are dormant, like spores. In their dormant form they can travel from one person or animal to another.

There are several different species of chlamydia, and a number of strains within each species that are responsible for a variety of diseases in birds, humans, and other mammals. Their most common appearance is as a sexually transmitted genital infection referred to as chlamydia or nongonococcal urethritis (NGU).

It is the most common sexually transmitted disease (STD) in the United States, especially among sexually active teens and young adults, totaling roughly four million cases each year. This strain also causes Reiter’s syndrome (arthritis, conjunctivitis , and urethritis ) and neonatal infections— pneumonia or conjunctivitis (“pink eye”)—when transferred from an infected mother.

Other types of chlamydia can cause:

  • Another less common STD known as lymphogranuloma venereum (LGV)
  • An eye infection called trachoma or Egyptian ophthalmia that causes millions of cases of blindness in developing nations around the world. This infection is known in developed countries as inclusion conjunctivitis or inclusion blenorrhea
  • Lung, heart, and intestinal infections

Causes

Genital chlamydial infections are caused when Chlamydia trachomatis is transmitted during oral, vaginal, or anal sex from an infected partner. Other forms of chlamydia can be transmitted by nonsexual contact, such as flies, dirty hands, or other objects, as well as inhalation and childbirth.