The main objective of this study is to compare the intestinal microbiota in newly diagnosed rheumatoid arthritis (RA) with that from individuals without RA.

The first analysis will compare the proportion of filamentous bacteria in the intestinal microbiota between the two groups.

The secondary objectives of this study are :

• A. To compare between the two groups :
• a. The proportion of Proteus mirabilis in the intestinal microbiota;
• b . The proportion of species producing peptidyl arginine deaminase (PAD ) in the intestinal microbiota;
• c . The number of species found in the intestinal microbiota.
• B. To evaluate bacterial translocation (from the digestive tract) in newly diagnosed RA patients with and healthy volunteers without RA. (Bacterial translocation is a phenomenon in which live bacteria or a part of bacteria (e.g. LPS teichoïc acid) cross the intestinal barrier and reach the bloodstream.).
• C. To describe the ecology of the intestinal microbiota of newly diagnosed RA patients (characterization of species found according to their respiratory metabolism, according to their bacteriological characteristics, and according to whether or not the species are found significantly more frequently in patients with RA than in individuals without RA).

Inclusion Criteria for RA patients:

• The patient was correctly informed
• The patient must have given his/her informed and signed consent
• The patient must be insured or beneficiary of a health insurance plan
• No antibiotic treatments within the 30 days preceding inclusion
• Absence of digestive pathology
• RA diagnosis made within the past 12 months

Exclusion Criteria for RA patients:

• The patient has participated in another study within the past 3 months
• The patient is under judicial protection, or any kind of guardianship
• The patient refuses to sign the consent
• It is impossible to correctly inform the patient
• The patient is pregnant, parturient, or breastfeeding
• The patient has taken antibiotics in the 30 days preceding inclusion
• RA was diagnosed more than 12 months ago
• Digestive pathology

Inclusion Criteria for healthy volunteers (HV):

• The HV was correctly informed
• The HV must have given his/her informed and signed consent
• The HV must be insured or beneficiary of a health insurance plan
• Absence of digestive pathology
• No antibiotic treatments within the 30 days preceding inclusion
• Does not have RA

Exclusion Criteria for HVs:

• The HV has participated in another study within the past 3 months
• The HV is under judicial protection, or any kind of guardianship
• The HV refuses to sign the consent
• It is impossible to correctly inform the HV
• The HV is pregnant, parturient, or breastfeeding
• The HV has taken antibiotics in the 30 days preceding inclusion
• Digestive pathology
• Joint pathology of any kind (including inflammatory pathologies)

A total of 50 adult subjects will be included: 25 with newly diagnosed RA (<12 months) based on the American College of Rheumatology criteria, and 25 healthy volunteers without RA.