Patient admitted in intensive care unit (ICU) for acute infection whether it be viral or bacterial had major impairment of the immune response. One hallmark of the immune impairment is presence of immature granulocyte (IG) in blood. Depend of initial trigger (virus or bacteria) concentration, phenotype and function of IG seems to be different. In this prospective trial, immature granulocytes will be analyzed in depth in immunocompetent patients hospitalized in the intensive care unit for an acute viral or bacterial infection.

Granulocytes are a key actor of immune response during acute viral or bacterial infection. During their maturation in bone marrow they went from immature form to mature form. In physiological condition only mature form are present in blood. However, in case of acute viral or bacterial infection, immature granulocytes (CD10low/CD16low) could be released in blood. But concentration, phenotype and function of these IG seems to be different between bacterial and viral infection. Indeed, in bacterial infection, concentration of IG is high (> 20%) and they expressed CD64 and CD123. In case of viral infection, blood concentration of IG is lower and they expressed CD62-L. These phenotype differences are probably associated with functional modification. A more precise characterization of the phenotype and functions of IG according to the stimulus (bacterial or viral) could provide a better understanding of the innate immune response in patients hospitalized in ICU for acute infection. The investigators will analysis by flow cytometry IG subsets (PDL1 CD62L LOX-1 CD45 CD64 CD15 CD123 CD16 CD10 CRTH2) of adult immunocompetent patient hospitalized in ICU for less than 24 hours for acute infection. Transcriptomic and cytokine analysis will be also performed. Infectious status will be validated by a blind adjudication committee which will classify patient in certain bacterial infection, certain viral infection, co-infection and no confirmed infection.

Inclusion Criteria:

• Bacterial infection:

  • Adult patient hospitalized for less than 24 hours in ICU for community documented sepsis
  • Vasopressor support
  • SOFA score > 4

• Viral infection:

  • Adult patient hospitalized for less than 24 hours in ICU for confirmed viral acute infection.
  • High flow oxygen, non-invasive or invasive ventilation since less than 24 hours
  • Moderate to severe ARDS with PaO2/FiO2 < 200mmHg and a FiO2 ≥ 0.6.

Exclusion Criteria:

• Bacterial infection:

  • Antibiotics or hospitalized in ICU in the previous 3 months
  • Immunocompromized patient
  • Ongoing acute or chronic viral infection

• Viral infection:

  • Antibiotics or hospitalized in ICU in the previous 3 months
  • Immunocompromized patient
  • Current antibiotics
  • Ongoing chronic viral infection.