May 6 (HealthDay News) -- Chlamydia infection may play a role in a type of arthritis called undifferentiated spondyloarthropathy (uSpA), a new study finds.

This form of arthritis is a type of spondyloarthritis (SpA), a group of diseases that share clinical features such as inflammatory back pain and inflammation at sites where tendons attach to bones. Other SpAs include ankylosing spondylitis, psoriatic arthritis, inflammatory bowel disease-related arthritis and reactive arthritis (ReA), according to background information in the release.

Chlamydia trachomatis or Chlamydia pneumoniae frequently cause ReA. The new study, published in the May issue of Arthritis & Rheumatism, looked at whether there was a link between these two infections and uSpA.

The University of South Florida researchers compared blood and synovial tissue samples from 26 patients with chronic uSpA or chlamydia-induced ReA with synovial tissue from a control group of 167 osteoarthritis patients. The 26 patients also underwent evaluation of swollen and tender joints and other symptoms of SpA and were asked about known chlamydia infection.

The researchers found that the rate of chlamydia infection in the patients with uSpA was 62 percent, compared with 12 percent in the control group.

SOURCE: Arthritis & Rheumatism, news release, April 30, 2009