Spondyloarthritis (SpA) is a group of inflammatory rheumatic disorders that mainly manifested by inflammatory pain of the spine, pelvis and sometimes limbs. Classically, SpA has been classified into several subtypes, such as ankylosing spondylitis (AS), psoriatic arthritis (PsA), inflammatory bowel disease (IBD)-associated.

Several studies have shown specific changes in the gut microbiota during SpA. A recent, uncontrolled study suggested that the therapeutic response to anti-TNFα (Tumor Necrosis Factor) therapy could be predicted by analysis of the gut microbiota.

The purpose of the study MEDIBIOTE 3 is to confirm that in SpA, the composition of the intestinal microbiota at the initiation of treatment is predictive of the response to treatment with biotherapy (anti-TNFα / anti-IL17).

Inclusion Criteria:

For patient with spondyloarthritis:

• Diagnosed for spondyloarthritis or pure axial or axial type psoriatic rheumatism according to Assessment of Spondyloarthritis International Society (ASAS) criteria.
• Requiring treatment with anti-TNFα or anti- IL-17 according to the treatment recommendations of the French Society of Rheumatology (SFR)
• patient not previously treated with biotherapy
• Aged ≥ 18 years
• Having given free and informed written consent
• Being affiliated to the center national security system social

For control Subject:

• Healthy volunteers without diagnosis of spondyloarthritis or any other chronic disease.
• Aged ≥ 18 years
• Having given free and informed written consent
• Being affiliated with or benefiting from a social security scheme.

Exclusion Criteria:

• Persons treated with antibiotics, probiotics, prebiotics or any other treatment that may disrupt the gut microbiota within one month before stool sampling.
• Association with another chronic pathology