Among winter respiratory viruses, influenza is the most common and therefore responsible for the highest mortality, but parainfluenza and RSV viruses have an even higher risk of mortality (1.6 to 1.9 times), this toll being paid mainly by the elderly and co-morbid population. Futhermore, SARS-Cov2 will probably become endemic and/or epidemic with the same targets of fragile patients. These viral infections are serious, however a bacterial co-infection worsens the prognosis even more: excess risk of mortality = 2.6, 95% CI [1.9-3.7].

Although rare, these co-infections are the subject of a prescription of antibiotics in more than 50% of influenza infections or other serious viral infections. Mainly due to this excess risk of mortality associated with the difficulty of diagnosing these co-infections.

Proper antibiotic use requires preventing this misuse and its harmful consequences in the short and long term at all costs. It is therefore imperative to have solid (grade A) evidence showing that antibiotic therapy in viral infections is not only futile but also potentially harmful.

Inclusion Criteria:

• Patients ≥ 65 years affiliated to a social security scheme

• Hospitalized for a lower respiratory infection defined as:

  • the presence of 2 of the following 4 signs:
  • hyperthermia >38°C,
  • hyperleukocytosis ≥12000 or ≤4000,
  • purulent aspirations/sputum,
  • rales on pulmonary auscultation indicating parenchymal damage
  • associated with a pulmonary image (standard X-ray, CT scan or ultrasound)

• Microbiological diagnostic sample taken within 48 hours

• Informed consent of the patient or their representative

Exclusion Criteria:

• Hospitalization planned for < 48 hours or transfer planned to another center within 7 days

  • Patient in septic shock,
  • Febrile aplasia
  • Absence of diagnostic microbiological sampling (> 48 hours after admission)
  • Moribund patient,
  • Death expected within the week
  • Inhalation proven by endoscopy or eyewitness
  • Purulent pleurisy, lung abscess, or other concomitant bacterial infection requiring antibiotic therapy.