Community-acquired pneumonia (CAP) is frequently suspected in the Emergency Department (ED). However, usual diagnosis procedure based on clinical features and chest X-Ray has rather bad performances.

A recent study on CT performance in suspected CAP found that 58% of classifications were modified by CT when compared with usual procedure. However, extended CT usage in CAP diagnosis is associated with many limitations :

availability in a majority of ED, delay, cost and irradiation, in particular In young patients.

Lung Ultrasound (LUS) has good performances in CAP diagnosis even when compared with CT. It is a rapid, inexpensive, radiation-free tool available in a majority of ED. It is performed at the patient's bedside with immediate results. The learning curve allows Emergency Physicians (EP) to perform this exam after a relative brief training.

The Investigators aim to investigate LUS performances in clinically suspected CAP authentication , and assesses specific diagnostic contributions and impact on antibiotic prescriptions .

120 patients will be enrolled on CAP suspicion. All explorations (radiography…) and biological exams (blood culture…) will be performed as usual to build physician primary diagnosis. Complementarily, an EP will be realized and final diagnosis will be made by physician. Finally, at Day28 expert adjudication committee will authentic diagnosis considering explorations and clinical issues. Frequency of discordant diagnosis between 1st and 2nd assessment and against expert will be measured Primary Purpose: diagnostic Study Phase: Not Applicable Intervention Model: NA Number of Arms: 1 Masking: open label, Masked Roles: NA Allocation: NA Study Endpoint Classification: efficacy Enrollment: 120 subjects (anticipated )

Inclusion Criteria :

- clinical suspicion of PAC

Exclusion Criteria :

• documented end-of-life
• pregnancy
• seriously ill patients

120 patients will be enrolled on CAP suspicion. All explorations (radiography…) and biological exams (blood culture…) will be performed as usual to build physician primary diagnosis. Complementarily, an EP will be realized and final diagnosis will be made by physician. Finally, at Day28 expert adjudication committee will authentify diagnosis considering explorations and clinical issues. Frequency of discordant diagnosis between 1st and 2nd assessment and against expert will be measured