Chlamydia is the most common treatable STD.

There are 3 species of chlamydia, Chlamydia psittaci, Chlamydia pneumoniae, and Chlamydia trachomatis.

Chlamydia trachomatis is a major cause of sexually transmitted diseases called nongonococcal urethritis and pelvic inflammatory disease.

When a woman with an active chlamydial infection gives birth to a baby, the baby mayaspirate (suck into his or her lungs) some of the mother's bacteria-laden secretions while passing through the birth canal. This can cause a form of relatively mild pneumonia in the newborn, occurring about two to six weeks after delivery.

Chlamydia psittaci is a bacteria carried by many types of birds, including pigeons, canaries, parakeets, parrots, and some gulls.

Humans acquire the bacteria through contact with dust from bird feathers, bird droppings, or from the bite of a bird carrying the bacteria. People who keep birds as pets or who work where birds are kept have the highest risk for this type of infection.

This pneumonia, called psittacosis, causes fever, cough, and the production of sputum containing pus. Psittacosis may be quite severe, and is usuallymore serious in older patients. The illness can last several weeks.

Chlamydia pneumoniae usually causes a type of relatively mild. Patients experience fever and cough. This type of pneumonia is called community-acquired pneumonia because it is easily passed from one member of the community to another.