Procalcitonin Antibiotic Consensus Trial (ProACT)

Inclusion Criteria: * ≥ 18 years old * A primary clinical diagnosis in the ED of acute LRTI (\< 28 days duration) * Clinician willing to consider procalcitonin in antibiotic decision-making Exclusion Criteria: * Systemic antibiotics before ED presentation (All prophylactic antibiotic regimens, OR received \>1 dose within 72 hours prior to ED presentation) * Current vasopressor use * Mechanical ventilation (via endotracheal tube) * Known severe immunosuppression * Accompanying non-respiratory infections * Known lung abscess or empyema * Chronic dialysis * Metastatic cancer * Surgery in the past 7 days (excluding minor surgery such as skin biopsy) * Incarcerated or homeless * Enrolled in ProACT in the past 30 days