Spontaneous Bacterial Peritonitis (SBP): Diagnosis, Treatment and Prevention in Cirrhosis

Spontaneous bacterial peritonitis (SBP) is an acute infection of ascitic fluid in cirrhotic patients — occurring without any obvious intra-abdominal source such as bowel perforation or abscess. It is one of the most life-threatening complications of cirrhosis, with an in-hospital mortality of 15–30% and a 1-year mortality exceeding 60% in those who survive without liver transplantation. As a hepatologist managing decompensated cirrhosis at Gleneagles Hospital Mumbai, I perform diagnostic paracentesis as a routine first step in any cirrhotic patient admitted with clinical deterioration, ascites worsening, or altered sensorium — because missing SBP is a potentially fatal oversight.

How Does SBP Occur?

SBP develops through bacterial translocation — bacteria from the gut (primarily gram-negative enteric organisms) crossing the intestinal wall into mesenteric lymph nodes, entering the systemic circulation, and seeding the ascitic fluid. Three factors make cirrhotics uniquely vulnerable:

• Impaired gut barrier: Cirrhosis causes intestinal dysmotility, bacterial overgrowth, increased intestinal permeability (leaky gut), and dysbiosis — all promoting bacterial translocation.
• Deficient ascitic fluid opsonic activity: Low ascitic fluid protein concentration (<15 g/L) means poor complement activity and opsonisation — bacteria that enter the peritoneal cavity are not effectively killed.
• Immune paresis: Cirrhosis impairs neutrophil function, complement synthesis, and reticuloendothelial system (RES) activity — the systemic immune defences are weakened precisely when bacterial load is highest.

The most common causative organisms are Escherichia coli (accounts for ~40%), Klebsiella pneumoniae (~20%), and other gram-negative bacilli. Gram-positive organisms (streptococcal species, staphylococci) account for ~20–30%, with their proportion increasing in healthcare-associated SBP. Anaerobes are rare — their absence helps distinguish SBP from secondary bacterial peritonitis.

Risk Factors for SBP

• Ascitic fluid total protein <15 g/L — the single strongest predictor of first SBP
• Prior episode of SBP — 40–70% recurrence rate within 1 year without prophylaxis
• Gastrointestinal haemorrhage — acute bleeding dramatically increases bacterial translocation risk
• Advanced cirrhosis: Child-Pugh C, MELD >15, bilirubin >3 mg/dL
• Proton pump inhibitor (PPI) overuse — PPIs alter gut microbiota and increase SBP risk; avoid routine use in cirrhotics without clear indication
• Renal impairment — AKI or CKD increases susceptibility

Recognising SBP: Clinical Features

The clinical presentation of SBP is deceptively variable. Classic features — fever, abdominal pain, abdominal guarding — are present in fewer than half of patients. The presentation is often subtle:

• Fever (present in ~50%): often low-grade; hypothermia can occur in severe cases
• Abdominal pain or tenderness (~50%): diffuse, not localised
• New or worsening ascites
• Hepatic encephalopathy without other explanation — HE in a cirrhotic with ascites should trigger diagnostic paracentesis even without fever or pain
• Acute kidney injury — complicates 30–40% of SBP episodes and is the main driver of mortality
• Asymptomatic (20–30%): detected only on routine paracentesis

Clinical pearl: Any cirrhotic patient with ascites who deteriorates — for any reason — warrants diagnostic paracentesis before or alongside other investigations. The cost of the procedure is trivial; the cost of missing SBP is a patient’s life.

Diagnosis of SBP

Diagnostic paracentesis involves withdrawing 20–30 mL of ascitic fluid using sterile technique. The key investigation is the ascitic fluid polymorphonuclear (PMN) neutrophil count:

• PMN ≥250 cells/mm³ = SBP diagnosis established — treat immediately, do not wait for culture
• Ascitic fluid culture (inoculated into blood culture bottles at bedside) is positive in only 40–50% of cases — a negative culture does not exclude SBP
• Ascitic fluid total protein, albumin (calculate SAAG: serum-ascites albumin gradient), glucose, LDH, and Gram stain should also be sent

Distinguishing SBP from Secondary Bacterial Peritonitis: Secondary peritonitis (from perforation, abscess) must be excluded because it requires surgery — and the treatment of SBP (antibiotics alone) would be fatal if given for a surgical cause. Features suggesting secondary peritonitis: ascitic fluid PMN very high (>10,000), protein >10 g/L, glucose <50 mg/dL, LDH > serum LDH, multiple organisms on culture. CT abdomen is mandatory if secondary peritonitis is suspected.

Treatment of SBP

Antibiotics

Start antibiotics immediately once PMN ≥250/mm³ is confirmed — do not wait for culture results. Every hour of delay worsens outcomes.

First-line: Cefotaxime 2g IV every 8 hours × 5 days — covers the predominant gram-negative organisms, penetrates ascitic fluid well, and has been validated in multiple RCTs. Alternatively, amoxicillin-clavulanate IV or oral ciprofloxacin 500 mg twice daily (in uncomplicated cases without vomiting, HE, or renal impairment).

Healthcare-associated SBP — defined as SBP developing ≥48 hours after hospital admission, or in patients recently hospitalised or on healthcare contact — has a higher prevalence of resistant organisms including ESBL-producing gram-negatives and MRSA. Empirical treatment should be escalated to carbapenems (meropenem) ± glycopeptides based on local resistance patterns. This is a growing clinical challenge in India where ESBL prevalence is high.

Repeat diagnostic paracentesis at 48 hours is recommended to confirm treatment response (PMN should fall by ≥25%). Failure to respond requires broadening antibiotic cover and reassessment for secondary peritonitis.

Albumin Infusion — Mandatory, Not Optional

Intravenous albumin given alongside antibiotics reduces mortality significantly. The landmark Sort et al. (NEJM 1999) trial showed albumin reduces hepatorenal syndrome from 33% to 10% and 3-month mortality from 29% to 10%.

Dosing: Albumin 1.5 g/kg IV on Day 1 (at diagnosis) + 1 g/kg IV on Day 3. Use 20% albumin solution. This is not optional — it is mandatory for any patient with SBP and bilirubin >4 mg/dL or creatinine >1 mg/dL. In patients with normal bilirubin and creatinine, albumin benefit is less established but increasingly used universally given the low risk.

Monitoring During Treatment

Daily creatinine, electrolytes, and urine output monitoring is essential. Hepatorenal syndrome (HRS-AKI) is the most dangerous complication — a rise in creatinine >0.3 mg/dL within 48 hours signals HRS and requires immediate terlipressin + albumin protocol initiation, ICU-level monitoring, and urgent transplant evaluation.

SBP Prophylaxis — Preventing the Next Episode

Secondary Prophylaxis (After First SBP Episode)

Every patient who survives SBP requires indefinite antibiotic prophylaxis — the recurrence rate without it is 40–70% per year. Norfloxacin 400 mg/day orally is the standard regimen (EASL 2018). Where norfloxacin is unavailable, ciprofloxacin 500 mg/day or trimethoprim-sulfamethoxazole are alternatives. Secondary prophylaxis is continued until liver transplantation or death. The high recurrence rate is itself an indication to accelerate transplant listing.

Primary Prophylaxis

Two high-risk groups benefit from primary SBP prophylaxis before any episode occurs:

• Low ascitic fluid protein <15 g/L with Child-Pugh ≥9 AND bilirubin ≥3 mg/dL or renal impairment (creatinine ≥1.2 mg/dL, sodium ≤130): norfloxacin 400 mg/day
• Acute gastrointestinal haemorrhage: ceftriaxone 1g IV/day × 7 days (superior to oral fluoroquinolones in this setting — Fernández et al., Gastroenterology 2006)

SBP and Liver Transplantation

A first episode of SBP is a pivotal moment in the natural history of cirrhosis. Median survival after SBP without transplantation is less than 1 year. Patients who develop SBP should be referred for transplant evaluation urgently if not already listed. I routinely evaluate international patients — from the UK, UAE, USA, Canada, East Africa — who have developed SBP as part of their decompensated cirrhosis and require transplantation in India. See liver transplant in India for NRI patients for the pathway.

Frequently Asked Questions About SBP

Can SBP be treated at home?

No — SBP requires hospitalisation for IV antibiotics, IV albumin, and close monitoring of kidney function. Oral antibiotic regimens are reserved for very carefully selected uncomplicated cases (no HE, no renal impairment, no vomiting, bilirubin <4) and even then require very close outpatient follow-up within 48 hours with repeat paracentesis to confirm response.

How is SBP different from regular peritonitis?

SBP is “spontaneous” — it occurs without any breach in the gut wall or intra-abdominal source. Regular (secondary) bacterial peritonitis results from a perforated viscus, abscess, or surgical complication. They look different on ascitic fluid analysis (SBP: single organism, lower protein; secondary: multiple organisms, high protein, high LDH, low glucose) and require completely different management — secondary peritonitis needs surgery, SBP does not.

Does SBP mean I need a liver transplant?

Not necessarily immediately, but SBP is a strong signal that your liver disease has reached a stage where transplant evaluation is warranted. The 1-year mortality after first SBP without transplantation is very high. Your hepatologist should begin the transplant work-up conversation after a first SBP episode if not already started.

Why do cirrhotics get infections so easily?

Cirrhosis causes a state of “cirrhosis-associated immune dysfunction” (CAID) — impaired neutrophil function, reduced complement production, altered monocyte/macrophage activity, and a chronically activated but poorly effective inflammatory state. The gut becomes leaky, allowing bacteria to translocate. The result is a patient who is simultaneously pro-inflammatory (high inflammatory markers) yet immunocompromised — vulnerable to infections that a healthy liver would clear easily.

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Dr. Chetan Kalal is a DM Hepatologist (ILBS, New Delhi) and liver transplant physician at Gleneagles Hospital, Mumbai — the first DM Hepatologist of Maharashtra and AASLD Foundation Award recipient. ORCID: 0000-0002-5284-7890. For consultations including telemedicine for international patients, contact the clinic.