Chlamydia trachomatis: A bacterium that causes a disease called trachoma that results in blindness so frequently that it places a huge burden a year on world health funding ($25 billion in the year 2000). The disease goes by a number of names such as sandy blight.

The transmission of Chlamydia trachomatis is mainly among children and from children to women during child care. Key risk factors include low socioeconomic status and inadequate supplies of water.

Trachoma affects approximately 500 million people worldwide, primarily in rural communities of the developing world and in the arid areas of tropical and subtropical zones. About 6-9 million people worldwide are currently blind and many more have suffered partial loss of vision from trachoma. Australia is the only developed country where trachoma is still a significant health problem; there it affects an estimated 100,000 people.

The mass treatment of trachoma with tetracycline ointment is effective in the short term, but the disease usually returns within 6-12 months to pretreatment levels in a community. Trachoma can now also be treated with the antibiotic azithromycin (brand name: Zithromax). Promotion of increased face-washing helps further to control the disease. Surgery of the scarred eyelids can prevent continued damage to the cornea by turned-in lashes.