## Most Common Causative Organism in Septic Shock **Key Point:** Gram-negative bacteria, particularly *Escherichia coli*, account for approximately 60–70% of septic shock cases in hospitalized patients globally and in India. ### Epidemiology of Septic Shock Organisms | Organism | Frequency | Common Source | Risk Factors | |----------|-----------|---------------|---------------| | *E. coli* | 60–70% | Urinary tract, intra-abdominal | Indwelling catheters, abdominal surgery | | *Klebsiella pneumoniae* | 15–20% | Respiratory, urinary | Diabetes, CKD, aspiration | | *Pseudomonas aeruginosa* | 10–15% | Respiratory, wounds | ICU stay, mechanical ventilation | | *S. aureus* | 5–10% | Skin, intravascular devices | IV lines, prosthetic devices | **High-Yield:** *E. coli* is the single most common organism in community-acquired sepsis and remains the leading cause even in hospital-acquired infections when all sources are considered. ### Clinical Context In this patient: - Diabetes and CKD are risk factors for urinary tract infection (UTI) → *E. coli* bacteremia - *E. coli* produces endotoxin (lipopolysaccharide), triggering the septic cascade - Early recognition and empiric coverage with broad-spectrum antibiotics (e.g., 3rd-generation cephalosporin or fluoroquinolone) is critical **Clinical Pearl:** Although *Klebsiella pneumoniae* is increasingly common in Asia (particularly in respiratory and urinary sources), *E. coli* remains the overall most frequent cause of septic shock when all sites are considered. **Warning:** Do not confuse "most common in ICU" (where *Pseudomonas* and *S. aureus* are more prevalent) with "most common overall" — the question asks about hospitalized patients broadly. [cite:Harrison 21e Ch 297]
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