The research hypothesis is based on a suspected strong involvement of the immune system in the genesis of serious manifestations of the disease (hepatitis, renal failure, thrombocytopenia, intra-alveolar hemorrhage). The question asked is that of the state of the immune system (quantitative and qualitative: activation markers, production of cytokines) evaluated by the study of circulating innate immune cells (monocytes, neutrophils, dendritic cells, lymphocytes, platelets).

Inclusion Criteria:

• Age ≥ 4 years;
• Weight ≥ 11 kg;
• with ongoing symptoms compatible with a clinical diagnosis of leptospirosis.
• AND having a diagnosis of leptospirosis confirmed according to standard care procedures: preferably by Polymerase Chain Reaction (PCR) (blood or urine) or, failing that, serology indicating a recent infection (positive Immunoglobulin M (IgM) or Microscopic Agglutination Test (MAT) technique with titer >1/400 for a pathogenic serogroup)
• AND affiliated to a Social Security scheme

Exclusion Criteria:

• Refusal of participation by the patient or his entourage if the patient is physically unable to give his opinion (coma, resuscitation, etc.).
• Not affiliated with social security
• Immunosuppression that may interfere with the interpretation of the results: chemotherapy in progress, immunosuppressants in progress for organ transplantation or autoimmune disease
• Patient under legal protection (Guardianship, Curators)