What are the risk factors for spontaneous bacterial peritonitis (SBP)?

Risk Factors for Spontaneous Bacterial Peritonitis

All patients with cirrhosis and ascites are at risk for SBP, with specific high-risk groups requiring heightened surveillance and prophylaxis consideration. 1

Patient Population at Risk

Baseline Risk:

• Prevalence in outpatients: 1.5-3.5% 1
• Prevalence in hospitalized patients: 10-11.3% 1
• Half of SBP episodes are present at hospital admission, while the remainder develop during hospitalization 1

High-Risk Clinical Factors

Advanced Liver Disease

• Child-Pugh Class C cirrhosis is an independent risk factor (OR: 3.323), with 85% of SBP cases occurring in this population 2, 3
• Elevated MELD score independently predicts both SBP development and mortality (OR: 1.565 for 30-day mortality) 2

Low Ascitic Fluid Protein

• Ascitic fluid protein concentration <10-15 g/L (1.0-1.5 g/dL) is a major risk factor requiring primary prophylaxis 4
• This reflects impaired opsonic activity and reduced local immune defense 4

Hyponatremia

• Serum sodium <125 mM is an independent predictor of SBP development (OR: 0.917 per mM increase) 2
• SBP-naïve patients with hyponatremia are at highest risk 2

Elevated Ascitic Fluid PMN Count

• Ascitic fluid PMN count ≥100 cells/μL (even below the diagnostic threshold of 250) indicates significantly increased risk for developing SBP (OR: 1.544) 2
• These patients warrant closer monitoring 2

Clinical Scenarios Requiring Immediate Paracentesis

Gastrointestinal Bleeding

• All cirrhotic patients with acute GI bleeding require antibiotic prophylaxis, as bacterial infections occur in 25-65% and significantly increase rebleeding rates and mortality 4
• This represents one of the highest-risk scenarios for SBP development 4

Prior Episode of SBP

• History of previous SBP is the strongest predictor of recurrence, with 1-year survival of only 34% after hospitalization with SBP 1
• These patients require indefinite secondary prophylaxis 4

Pathophysiologic Risk Factors

Bacterial Translocation

• Portal hypertension leads to increased intestinal permeability and bacterial translocation from the gut 1, 5
• Gut dysbiosis and bacterial overgrowth facilitate this process 1, 5

Immune Dysfunction

• Cirrhosis-associated immune dysfunction impairs the ability to clear translocated bacteria 1, 5
• Genetic factors, particularly NOD2 variants affecting bacterial recognition, increase SBP risk 1

Medication-Associated Risk Factors

Acid Suppression

• Proton pump inhibitors and other acid suppressive therapies are strongly associated with SBP in at-risk individuals 6
• Consider withholding these medications when possible 6

Beta-Blockers in Advanced Disease

• Beta-adrenergic antagonist therapy is associated with SBP risk, particularly in end-stage liver disease with refractory ascites 6
• Discontinuation should be considered in patients with resistant ascites 6

Healthcare-Associated Risk Factors

Nosocomial Acquisition

• Healthcare-associated and nosocomial SBP show increased rates of multidrug-resistant organisms and gram-positive infections 6, 7
• Prior fluoroquinolone prophylaxis shifts the bacterial epidemiology toward gram-positive cocci and quinolone-resistant organisms 4, 6

Common Pitfalls

Critical Warning: Each hour of delay in diagnostic paracentesis after hospital admission is associated with a 3.3% increase in in-hospital mortality after adjusting for MELD score 1. Therefore, maintain a low threshold for performing diagnostic paracentesis in any cirrhotic patient with ascites who presents with fever, abdominal symptoms, altered mental status, worsening liver/renal function, hepatic encephalopathy, shock, or GI bleeding 1.

Important Note: SBP may be completely asymptomatic, particularly in outpatients, making routine surveillance paracentesis essential in high-risk populations 1.