Aseptic abscess syndrome (AA) is a rare entity characterized by the occurrence of deep abscesses with no germ found. Antibiotic therapy is ineffective and they are sensitive to anti-inflammatory treatment with corticosteroids.

Gut microbiota is important for the development of the immune system. In Crohn's disease which is frequently associated with AA syndrome, dysbiosis is found but could also be involved in the immune response at a distance from the gut.

Stool, blood, saliva and urine samples will be taken from the patients included and their controls in the centers where they are followed. These biological samples will be transported to Clermont Ferrand using the same procedure (transporter and dry ice) where the following analyses will be performed: microbiota on stool and saliva, short chain fatty acids on stool and lymphocyte study on blood.

• Included patients will be adult patients meeting the diagnostic criteria for aseptic abscess syndrome described by André et al.
• Controls will be adults without aseptic abscess syndrome living in the same environment as the patients, whether related to the patient or not.

Patients and controls must be able to provide informed consent and be affiliated with the French Social Security system.

Inclusion Criteria:

• For cases: adult patients meeting the diagnostic criteria for aseptic abscess syndrome described by André et al:
• Deep abscesses on radiological examination with neutrophilic features proven by pathological analysis of a surgical specimen or biopsy when performed
• Negative blood cultures, negative serological tests for bacteria, including always Yersinia enterocolitica, and, during surgery or aspiration, sterile pus (with standard cultures, BAAR and fungal tests) Failure of antibiotic therapy, when prescribed, after at least 2 weeks for conventional antibiotic therapy and at least 3 months for anti-tuberculosis treatment
• Rapid clinical improvement the day after the prescription of corticosteroids (at least 1/2 mg/kg prednisone or equivalent) followed by radiological improvement after 1 month of corticosteroids, sometimes in association with immunosuppressive treatments.

For controls: adult person living in the same environment as the case to which it is matched. Adult person living in the same household or near the patient.

For cases and controls:

• Ability to provide informed consent.
• Membership in the Social Security system.

Exclusion Criteria:

• Pregnant women. Incapable patients Patients deprived of liberty Antibiotic therapy administered within 6 weeks prior to inclusion.