A clinician must choose empiric therapy for severe sepsis of unknown bacterial source. Which of the following is the best reason to start a broad-spectrum agent rather than a narrow-spectrum agent?

• A. Starting with broad-spectrum therapy removes the requirement for diagnostic testing and microbiology support because subsequent lab confirmation becomes clinically irrelevant.
• B. Narrow-spectrum antibiotics are never effective in severe infections because severe infections are always polymicrobial and comprise both Gram-positive and Gram-negative organisms.
• C. Broad-spectrum agents permanently prevent resistance and therefore should always be selected regardless of culture availability or patient risk factors.
• D. Broad-spectrum therapy increases the probability of covering the causative pathogen rapidly in life-threatening infections when immediate, appropriate coverage is critical, while accepting the need to de-escalate once culture data are available.

Answer: (D)