Chlamydia infection may play a role in a type of arthritis called undifferentiated spondyloarthropathy (uSpA), researchers at the University of South Florida found.

This form of chronic arthritis belongs to a group of arthritis diseases (spondylarthritides or SpA) that share clinical features such as inflammatory back pain and inflammation at sites where tendons attach to bone. Ankylosing spondylitis, psoriatic arthritis, inflammatory bowel disease-related arthritis, reactive arthritis (ReA) are among other SpAs.

Chlamydia trachomatis or chlamydia pneumoniae (which are often asymptomatic) frequently cause ReA. The new study, published in the May 2009 issue of Arthritis & Rheumatism, examined whether there was a connection between these two infections and uSpA.

Led by John D. Carter, MD, associate professor and chief of Rheumatology at the USF College of Medicine, the study compared blood and synovial tissue samples from 26 patients who had chronic uSpA or Chlamydia-induced ReA with synovial tissue samples from a control group of 167 osteoarthritis patients. The patients were asked about any known Chlamydia infection and underwent a physical exam evaluating swollen and tender joints and other symptoms of SpA.

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

An estimated 150,000 cases of chlamydia trachomatis-induced ReA may appear in the U.S. each year compared to about 125,000 new cases of rheumatoid arthritis. This estimate is low, because it does not include cases resulting from chlamydia pneumoniae. “Thus, Chlamydia-induced ReA represents a considerable burden on the health care systems of the U.S. and other nations, and its impact on those systems may well be significantly underrecognized,” the authors state.

Most women with genital chlamydia trachomatis infection have no symptoms at initial infection; this was also true of the patients in the study with DNA evidence of chlamydia. For chlamydia pneumoniae, as many as 70 percent of acute infections are asymptomatic and, even when symptoms exist, definitive identification of the organism is rare. The authors point out that relying on identification of a symptomatic infection may result in routine underdiagnosis or misdiagnosis of chlamydia-induced ReA.

Since ReA is a type of SpA and patients with ReA do not experience the classic combination of arthritis symptoms — conjunctivitis/iritis and urethritis — it is reasonable to believe that Chlamydia trachomatis plays a role in causing uSpA, which may in fact be ReA, the researchers write. They conclude that testing for chlamydial DNA in the synovial tissue of patients thought to have ReA may be the most accurate way of diagnosing the condition.

Study co-authors included Joanne Valeriano, MD, and Frank Vasey, MD, from USF Health.