Evaluation criteria. Attending ED physicians will implement pre- and post-test proforma for diagnosis (CAP) level of certainty, treatment (antimicrobial agents), site of care, before and after chest CT-scan. Comparison of ED physician's answers before/after CT-scan. Patients will be followed until day 28. An adjudication committee (1 pneumologist, 1 infectiologist, 1 radiologist)will review patients' data for gold standard diagnosis.