Chlamydia damages the host cell it infections and causes inflammation as the 2nd line defenses try to kill the bacteria. Hard to kill because it is hiding in our cells that the phagocytes recognize as self. These bacteria are too small to see with the light microscope and are difficult to culture in the lab. Hard to diagnose. Virulence factors come from Chlamydia's ability to hide from the immune system after stimulating it.
Infertility is the ultimate result of chronic inflammation in the male or female genital tract.
Chlamydia infections resemble gonococcal infections because they are both inflammatory diseases. The symptoms are the same because it is the immune system that is doing the damage not the microbe. Blindness results from scaring in the eye. Hardening of the arteries is only hypothesized as being caused by this species of bacteria. There is some evidence that Chlamydia is the cause of clogged arteries and the fatty plaques that lead to blocked coronary arteries and heart attacks.