Chlamydia trachoma and pneumonia can cause reactive arthritis; and chlamydia psittacosis can cause psoriatic arthritis. PCR negative arthritis patients were shown to have chlamydia in the joint, based on direct PCR testing of synovial tissue. Long-term antibiotic treatment (six months), with two antibiotics effective against chlamydia, resolved symptoms and eradicated persistent infection. In arthritis, PCR testing may be negative, even though chronic infection persists in tissue.
Chlamydia trachoma, pneumonia, and psittacosis can spread from the initial infection site and establish live organisms, throughout the body, including in synovial tissue. Chronic chlamydia infection in the joint synovial tissue triggers an inflammatory response from the immune system.