Spontaneous Bacterial Peritonitis - Symptoms, Causes, Treatment & Prevention

Overview

Spontaneous bacterial peritonitis (SBP) is an acute infection of the fluid that accumulates in the abdominal cavity (the peritoneal cavity) without an obvious source such as a perforated organ or an abdominal surgery wound. The infection typically occurs in patients who already have ascites, most commonly due to advanced liver cirrhosis. SBP is a medical emergency because it can rapidly progress to sepsis, organ failure, and death.

• Who it affects: Adults with cirrhosis and ascites; less commonly, patients with nephrotic syndrome, heart failure, or pancreatic disease may develop SBP.
• Prevalence: Approximately 10‑30 % of cirrhotic patients with ascites will develop at least one episode of SBP during their disease course. In hospitalized cirrhotics, the incidence is reported as 11‑14 % per year (Mayo Clinic, 2023).
• Mortality: Untreated SBP carries a mortality rate of 20‑30 %; even with appropriate antibiotics, 10‑20 % of patients die within 30 days (Cleveland Clinic, 2022).

Symptoms

SBP may present with vague or subtle findings, especially in patients with liver disease who already have abdominal discomfort. Common symptoms include:

• Fever or low-grade chills – often the first clue.
• Abdominal pain or tenderness – typically diffuse, sometimes localized to the right upper quadrant.
• Worsening ascites – rapid increase in abdominal girth.
• Altered mental status – confusion, asterixis, or hepatic encephalopathy.
• Nausea or vomiting – may be mistaken for medication side‑effects.
• Diarrhea – less common, but can occur.
• Hypotension or tachycardia – signs of systemic infection/sepsis.
• Generalized fatigue or malaise.

Because many of these symptoms overlap with other complications of cirrhosis (e.g., variceal bleed, hepatorenal syndrome), a high index of suspicion is essential.

Causes and Risk Factors

Pathophysiology

SBP arises when bacteria translocate from the intestinal lumen across a compromised gut barrier, then travel via the bloodstream or lymphatics into the ascitic fluid. The peritoneal cavity of cirrhotic patients is an ideal medium for bacterial growth because it is protein‑rich, low in complement, and has impaired phagocytic activity.

Typical organisms

• Gram‑negative bacilli – E. coli, Klebsiella spp. (≈ 60‑70 % of cases).
• Gram‑positive cocci – Streptococcus spp., Enterococcus spp. (≈ 20‑30 %).
• Multidrug‑resistant (MDR) organisms – increasingly common in patients with prior antibiotic exposure or recent hospitalization.

Risk factors

• Advanced liver cirrhosis (Child‑Pugh class B or C)
• Large volume ascites (> 2 L) or repeated paracenteses
• Low protein concentration in ascitic fluid (<1 g/dL)
• Renal dysfunction or hepatorenal syndrome
• Recent gastrointestinal bleeding
• Proton‑pump inhibitor (PPI) use – associated with intestinal bacterial overgrowth
• Prior SBP episode (risk of recurrence ~ 70 % within 1 year)
• Immunosuppression (e.g., HIV, chemotherapy)

Diagnosis

Prompt diagnosis relies on a combination of clinical suspicion, laboratory analysis of ascitic fluid, and supportive imaging.

Paracentesis – the cornerstone test

• Performed as soon as SBP is suspected, ideally within 1 hour of presentation.
• Polymorphonuclear (PMN) leukocyte count: ≥250 cells/mm³ is diagnostic even if cultures are negative.
• Gram stain and culture of the fluid should be sent before starting antibiotics.
• Additional fluid studies – total protein, albumin, glucose, lactate dehydrogenase (LDH) – help differentiate other causes (e.g., secondary peritonitis).

Blood tests

• Complete blood count (CBC) – leukocytosis may be blunted in cirrhotics.
• Serum creatinine, electrolytes, and liver panel – assess organ function.
• Serum-ascites albumin gradient (SAAG) – helps confirm portal hypertensive ascites (>1.1 g/dL).

Imaging

• Ultrasound – evaluates fluid volume, rules out intra‑abdominal abscesses, and guides safe paracentesis.
• CT scan – reserved for patients with atypical presentation or suspicion of secondary peritonitis (e.g., perforated viscus).

Diagnostic criteria (per 2022 AASLD guidelines)

SBP is diagnosed when any of the following are present:

1. PMN count ≥250 cells/mm³ in ascitic fluid, regardless of culture result.
2. Positive ascitic fluid culture with any PMN count.
3. Clinical signs of infection plus a rapid rise in ascitic fluid neutrophils on repeat paracentesis.

Treatment Options

Early empiric antibiotic therapy dramatically improves survival. Treatment is usually initiated before culture results return.

First‑line antimicrobial regimens

• Third‑generation cephalosporin: Cefotaxime 2 g IV every 8 h for 5 days (most widely used; covers common Gram‑negatives).
• Alternative: Ceftriaxone 2 g IV daily.

When MDR organisms are suspected

• Broad‑spectrum agents such as piperacillin‑tazobactam or a carbapenem (e.g., meropenem) plus coverage for resistant Gram‑positives (e.g., vancomycin) may be required.
• Therapy should be de‑escalated based on culture and sensitivity results.

Adjunctive measures

• Albumin infusion: 1.5 g/kg body weight on day 1, then 1 g/kg on day 3 (per NICE 2021) reduces risk of renal failure and mortality.
• Fluid resuscitation and electrolyte correction as needed.
• Discontinue or limit PPIs if not essential.

Management of complications

• Hepatorenal syndrome: Early nephrology consultation; consider vasoconstrictor therapy (e.g., terlipressin) plus albumin.
• Variceal bleeding: Endoscopic band ligation or pharmacologic therapy as per standard protocols.

Secondary prophylaxis

Because recurrence is common, long‑term antibiotic prophylaxis is recommended after an initial episode:

• Norfloxacin 400 mg orally once daily, or trimethoprim‑sulfamethoxazole 160/800 mg daily, for up to 6 months or indefinitely in high‑risk patients.
• Prophylaxis should be reassessed regularly for side effects and emerging resistance.

Lifestyle & supportive care

• Low‑sodium diet (<2 g/day) to control ascites.
• Regular therapeutic paracentesis when fluid volume threatens respiration or causes discomfort.
• Alcohol abstinence – critical for any cirrhotic patient.
• Vaccinations: hepatitis A & B, pneumococcal, influenza, and COVID‑19.

Living with Spontaneous Bacterial Peritonitis

Managing SBP is a team effort that includes hepatologists, primary‑care providers, dietitians, and caregivers. Practical daily tips:

• Monitor weight daily – a sudden increase of >2 kg in 48 h may indicate fluid accumulation.
• Keep a symptom diary (fever, abdominal pain, mental status changes).
• Adhere strictly to prescribed antibiotics; never stop early even if you feel better.
• Schedule regular follow‑up labs (CBC, renal function, liver panel) every 2–4 weeks.
• Limit salt: read labels, avoid processed foods, flavor meals with herbs, lemon, or vinegar.
• Stay hydrated but follow your provider’s fluid recommendations; excess free water can worsen ascites.
• Engage in gentle activity (e.g., short walks) as tolerated – helps maintain muscle mass and reduces portal hypertension.
• Carry a concise medical alert card stating “Cirrhosis with ascites – risk of SBP – on prophylactic antibiotics.”

Prevention

Because SBP is largely preventable, focus on modifiable factors:

• Primary prophylaxis: Initiate norfloxacin or trimethoprim‑sulfamethoxazole in cirrhotic patients with ascitic fluid protein <1 g/dL or a prior SBP episode.
• Control ascites: Use diuretics (spironolactone ± furosemide) to maintain a modest fluid balance; avoid large‑volume paracenteses without albumin replacement.
• Limit invasive procedures that breach the gut wall; when necessary, use prophylactic antibiotics (e.g., before endoscopy for variceal banding).
• Vaccinations – as listed above.
• Reduce PPI use – switch to H2 blockers if acid suppression is required.
• Alcohol cessation programs – counseling, support groups, and pharmacologic aid (naltrexone, acamprosate).

Complications

If SBP is not recognized promptly, a cascade of serious complications can develop:

• Septic shock – profound hypotension, organ hypoperfusion.
• Acute kidney injury / hepatorenal syndrome – occurs in up to 40 % of SBP patients.
• Hepatic encephalopathy – worsened mental status due to ammonia accumulation.
• Upper gastrointestinal bleeding – portal hypertension may precipitate variceal rupture during infection.
• Multiorgan failure – respiratory distress, coagulopathy, and cardiac dysfunction.
• Recurrent SBP – each episode increases mortality risk and may accelerate progression to end‑stage liver disease.

When to Seek Emergency Care

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Sources: Mayo Clinic. “Spontaneous bacterial peritonitis.” 2023; Cleveland Clinic. “SBP Overview.” 2022; American Association for the Study of Liver Diseases (AASLD) Practice Guidelines, 2022; National Institutes of Health (NIH) – LiverTox; World Health Organization (WHO) – Infectious disease fact sheets; CDC – Antibiotic resistance surveillance.