Any of the bacterial parasites that make up the genus Chlamydia , which cause several diseases in humans, including conjunctivitis and chlamydial pneumonia .
One form causes a variety of sexually transmitted diseases. In men, symptoms are similar to those of gonorrhea . In women, chlamydial infection ordinarily produces few, if any, symptoms, and most infected women thus are unaware of their condition. However, untreated infections in women can lead to sterility, a higher risk of premature births, and ectopic pregnancies . Chlamydia frequently causes conjunctivitis or pneumonia in the newborn infant. Treatment is with antibiotics.