 CLINPCT study is a prospective, randomized, controlled, open intervention clinical trial including adult patients admitted in the emergency department with community-acquired pneumonia. The objective of this clinical trial is to compare two strategies: clinical reassessment and procalcitonin guided diagnostic and therapeutic strategy in patients with community-acquired pneumonia. In the clinical reassessment arm, antibiotherapy is systematically started in the emergency department. The continuation, the discontinuation or the modification of the antibiotherapy initially prescribed in the ED were made at Day 1 and Day 5 based on clinical assessment. On Day 1, the aim of the clinical reassessment is diagnosis reassessment: to confirm or not the diagnosis of community-acquired pneumonia and to confirm or not the antibiotherapy. On Day 5, the aim of the clinical reassessment is to evaluate the possibility to stop the current antibiotherapy based on criteria for clinical stability defined by the Infectious Diseases Society of America Temperature 37.8C, Heart rate 100 beatsmin, Respiratory rate 24 breathsmin, Systolic blood pressure 90 mm Hg, Arterial oxygen saturation 90 or pO2 60 mm Hg on room air. In the procalcitonin arm, initiation and discontinuation of the antibiotherapy is based on the antibiotic stewardship based on procalcitonin PCT cut-off ranges previously published. Re-evaluation of the clinical status and measurement of serum PCT levels is mandatory after 6-24 h in all persistently sick and hospitalized patients in who antibiotic are withheld. The PCT algorithm can be overruled by pre-specified criteria, e.g. in patients with immediately life-threatening disease. If the algorithm is overruled and antibiotics are given, an early discontinuation of antibiotic therapy after 3, 5 or 7 days is more or less endorsed based on PCT levels. In hospitalized patients with ongoing antibiotic therapy PCT levels are reassessed on days 3, 5 and 7 and antibiotics will be discontinued using the PCT cut-offs defined above. 