SBP is most commonly (75%) caused by gram-negative aerobic organisms, with Klebsiella pneumonia accounting for 50% of these. Gram-positive aerobic organisms are responsible for the remainder of cases; the most common of these are Streptococcus pneumoniae or Viridans group streptococci.
The ascitic fluid typically has a high oxygen tension. Therefore anaerobic organisms are not commonly seen. In the majority of cases of SBP, only one infecting organism is involved (92%), though a small number of cases have been reported as polymicrobial.
Typically, patients who experience SBP have a chronic liver disease with a Child-Pugh classification, which assesses the prognosis of liver disease, of C. This ranking involves a high to a maximum score of 10 to 15 points (on the Child-Pugh scale), and measures 1-year patient survival at 45% and 2-year survival at 35%. Decompensated cirrhotic patients are those at highest risk of developing SBP. Infecting organisms typically originate from the intestinal lumen, from where they pass via translocation to mesenteric lymph nodes.
Additional risk factors for SBP include a previous history of SBP, low complement levels, and reduced hepatic synthesis of proteins with (1) an associated prolonged PT time and reduced protein levels in ascitic fluid (less than 1 g/dL), and (2) long-term proton pump inhibitor (PPI) therapy such as increased gastric pH with PPI use, which promotes gut bacterial growth and translocation.
Though in adults, SBP is typically seen in patients with abdominal ascites, most children with SBP do not have ascites. The reason for this has not yet been elucidated.
SBP can occur in adults and children. In children, it most commonly occurs in neonates and those around five years of age. It is most common in patients with cirrhosis, though it can occur as a complication of any disease that results in accumulation of ascitic fluid, such as liver disease, Budd-Chiari syndrome, congestive heart failure, systemic lupus erythematosus, renal failure, or cancers, and has a poor prognosis. Approximately 10% to 25% of patients with ascites will develop SBP, and the condition is associated with a 20% in-hospital rate of mortality.
Patients with a prior incidence of SBP are more likely to encounter a subsequent infection with a drug-resistant organism. Additionally, the risk of developing SBP increases with age, use of proton-pump inhibitors (PPIs), and when undergoing SBP prophylaxis such as selective intestinal decontamination. 
The majority of the isolated organisms in SBP (90%) are gram-negative enteric organisms (e.g., Escherichia coli or Klebsiella pneumoniae) which suggest that the main source of contamination is the gastrointestinal (GI) tract. Enterotoxin is also frequently isolated from ascitic fluid, further supporting the theory that bacteria involved in SBP migrate transmurally from the intestinal lumen (i.e., bacterial translocation).
An alternatively proposed mechanism of contamination involves hematogenous spread, from a distant source, such as a urinary tract infection, in individuals predisposed to the disease by a weakened immune system (i.e., immunocompromised). Patients with cirrhosis typically have an elevated level of bacterial overgrowth in the GI tract, largely due to a prolonged intestinal transit time. This, coupled with reduced protein production by a cirrhotic liver (e.g., low complement levels in both the serum and ascites) and poor phagocytic and reticuloendothelial system function, results in a decreased ability to clear microorganisms from the system, thereby further contributing to bacterial overgrowth, migration, and expansion within the ascites fluid.
One should have a high index of suspicion for SBP in all patients presenting with ascites, and this is especially true if the patient has an acute history of clinical deterioration. The majority of patients with SBP will present with fever, chills, and abdominal pain, although some patients may be asymptomatic and SBP is an incidental finding. Fever is the most common symptom encountered in patients with SBP, which is a particularly useful clinical symptom as patients with cirrhosis are typically hypothermic. Additional signs and symptoms include diarrhea, paralytic ileus, new-onset or worsening encephalopathy (e.g., altered mental status) without any other identifiable cause, new-onset or worsening renal failure, or presence of ascites that does not improve with use of diuretic medications.
On physical examination, most patients will have a tender abdomen, although patient response can vary from mild discomfort to the presence of guarding and rebound tenderness.
There is a short window of opportunity for treating SBP before it progresses to septic shock or multisystem organ failure; therefore, rapid assessment and diagnosis are critical (i.e., treatment is much more successful if antibiotics are started before the development of shock).
Peritoneal fluid analysis (e.g., cell count, differential, culture, lactate level, pH) should be performed in all patients with suspected SBP. This may be achieved either by diagnostic paracentesis or withdrawal of fluid through a peritoneal catheter, which is sometimes present in patients undergoing peritoneal dialysis. In patients with only a small amount of ascites, ultrasonography should be employed to help guide the paracentesis procedure.
Additionally, blood and urine cultures should be obtained before initiation of antibiotic therapy as the results of these may help point towards a source of infection and guide antibiotic therapy.
The most accurate predictor of SBP is a polymorphonuclear leukocyte (PMN or granulocytes such as neutrophils, basophils, and eosinophils) count of greater than 500 cells/uL in a sample of ascitic fluid with a sensitivity and specificity of 86% and 98%, respectively. At a PMN count of greater than 250cells/uL, sensitivity increases to 93% while specificity declines to 94%. This is the widely accepted number of PMNs needed to form a presumptive diagnosis of SBP, before beginning empiric antibiotic therapy.
If the perforation is suspected within the abdomen, imaging is warranted, and computed tomography (CT) should be strongly considered, as it is more sensitive for detecting smaller perforations than a plain radiograph.
More recently proposed tests for SBP include a rapid reagent strip that evaluates for the presence of leukocyte esterase in ascitic fluid, which is shown to have a sensitivity of 100% in the diagnosis of SBP when compared to manual PMN counting. Though this may prove to be a much more efficient method of SBP diagnosis than those previously used, the test still needs to undergo a large-scale comprehensive evaluation.
Empiric antibiotic therapy, such as intravenous third-generation cephalosporin, should be started in all patients with suspected SBP and a PMN count of greater than 250 cell/uL on ascitic fluid analysis. Exceptions to this rule include patients with recent beta-lactam antibiotic exposure or diagnosis of SBP in a nosocomial setting. Antibiotics should be chosen based on results of susceptibility testing in these cases.
Patients with an ascitic fluid PMN count of greater than 500cells/uL should be admitted and treated with empiric antibiotic therapy as soon as possible and the antibiotics adjusted later based on the results of susceptibility testing. A follow-up analysis of ascitic fluid to assess PMN count should be performed to ensure the patient is receiving adequate and appropriate antibiotic therapy. This is important, as lack of improvement after 48 hours of therapy may indicate an underlying perforation or abscess formation, such as secondary bacterial peritonitis, that may require surgery. In general, ascitic fluid PMN count should be reduced by at least 25% after 48 hours of antibiotic therapy.
Some cirrhotic patients with SBP and either a serum creatinine greater than 1mg/dL, a blood urea nitrogen (BUN) greater than 30mg/dL, or total bilirubin greater than 4mg/dL should be given adjunctive (i.e., in addition to antibiotics) albumin intravenously. This has been shown to reduce both in-hospital mortality and renal damage when compared to the use of antibiotic therapy alone.
Certain high-risk patients may benefit from outpatient antibiotic prophylactic therapy including norfloxacin, ciprofloxacin, or trimethoprim-sulfamethoxazole. These individuals have had a prior episode of SBP, or ascitic fluid with either a low protein count (< 1g/dL) or is associated with a GI bleed.
When patients develop ascites from whatever cause, the treatment usually involves a team of healthcare professionals including nurses, pharmacists, physicians, and other allied healthcare workers. These patients not only need to be treated for the acute infection but also the primary disorder causing the fluid build up. The patients are often emaciated and need a dietary consult. A physical therapy consult is needed to increase mobility and muscle function. The pharmacist must ensure that the patient is on no medications that can worsen liver or renal function and must abstain from alcohol use. The nurse has to monitor the patient's abdomen girth, body weight, and vital signs regularly to make sure that the treatment is working. The family has to be educated on the signs and symptoms of bacterial peritonitis and when to bring the patient back to the hospital. There is a small margin for errors and any delay in seeking help can lead to mortality.  (Level V)
Spontaneous bacterial peritonitis carries a mortality rate of 30-70% in patients with end-stage liver and kidney disease. The mortality rates are lower in children with nephrosis. Recently the mortality rates have shown a slight decrease because of earlier diagnosis and advances in treatment. For the patient who develops septic shock secondary to bacterial peritonitis, the mortality increases each hour until antibiotic therapy is started. (Level V)
|||Song DS, [Spontaneous Bacterial Peritonitis]. The Korean journal of gastroenterology = Taehan Sohwagi Hakhoe chi. 2018 Aug 25 [PubMed PMID: 30145857]|
|||Soin S,Sher N,Saleem N, Spontaneous bacterial empyema: an elusive diagnosis in a patient with cirrhosis. BMJ case reports. 2018 Aug 29 [PubMed PMID: 30158261]|
|||Maraolo AE,Gentile I,Pinchera B,Nappa S,Borgia G, Current and emerging pharmacotherapy for the treatment of bacterial peritonitis. Expert opinion on pharmacotherapy. 2018 Aug [PubMed PMID: 30071176]|
|||Oey RC,van Buuren HR,de Jong DM,Erler NS,de Man RA, Bacterascites: A study of clinical features, microbiological findings, and clinical significance. Liver international : official journal of the International Association for the Study of the Liver. 2018 Jul 11 [PubMed PMID: 29992711]|
|||Bolia R,Srivastava A,Marak R,Yachha SK,Poddar U, Prevalence and Impact of Bacterial Infections in Children With Liver Disease-A Prospective Study. Journal of clinical and experimental hepatology. 2018 Mar [PubMed PMID: 29743795]|
|||Oey RC,de Man RA,Erler NS,Verbon A,van Buuren HR, Microbiology and antibiotic susceptibility patterns in spontaneous bacterial peritonitis: A study of two Dutch cohorts at a 10-year interval. United European gastroenterology journal. 2018 May [PubMed PMID: 29881617]|
|||MacIntosh T, Emergency Management of Spontaneous Bacterial Peritonitis - A Clinical Review. Cureus. 2018 Mar 1 [PubMed PMID: 29721399]|
|||Wang H,Li Y,Zhang F,Yang N,Xie N,Mao Y,Li B, Combination of PCT, sNFI and dCHC for the diagnosis of ascites infection in cirrhotic patients. BMC infectious diseases. 2018 Aug 10 [PubMed PMID: 30097024]|
|||Yang L,Wu T,Li J,Li J, Bacterial Infections in Acute-on-Chronic Liver Failure. Seminars in liver disease. 2018 May [PubMed PMID: 29871019]|
|||Moreau R,Elkrief L,Bureau C,Perarnau JM,Thévenot T,Saliba F,Louvet A,Nahon P,Lannes A,Anty R,Hillaire S,Pasquet B,Ozenne V,Rudler M,Ollivier-Hourmand I,Robic MA,d'Alteroche L,Di Martino V,Ripault MP,Pauwels A,Grangé JD,Carbonell N,Bronowicki JP,Payancé A,Rautou PE,Valla D,Gault N,Lebrec D, Effects of Long-term Norfloxacin Therapy in Patients with Advanced Cirrhosis. Gastroenterology. 2018 Aug 22 [PubMed PMID: 30144431]|
|||Singh A,Cresci GA,Kirby DF, Proton Pump Inhibitors: Risks and Rewards and Emerging Consequences to the Gut Microbiome. Nutrition in clinical practice : official publication of the American Society for Parenteral and Enteral Nutrition. 2018 Aug 2 [PubMed PMID: 30071147]|
|||Luo WW,Zhang DZ, [Diagnosis and treatment of bacterial infection in patients with end-stage liver disease]. Zhonghua gan zang bing za zhi = Zhonghua ganzangbing zazhi = Chinese journal of hepatology. 2018 Jan 20 [PubMed PMID: 29804355]|
|||Caly WR,Abreu RM,Bitelman B,Carrilho FJ,Ono SK, Clinical Features of Refractory Ascites in Outpatients. Clinics (Sao Paulo, Brazil). 2017 Jul [PubMed PMID: 28792999]|
|||Harrison PM, Management of patients with decompensated cirrhosis. Clinical medicine (London, England). 2015 Apr [PubMed PMID: 25824076]|
|||Haj M,Hart M,Rockey DC, Development of a novel clinical staging model for cirrhosis using the Nationwide Inpatient Sample. Journal of investigative medicine : the official publication of the American Federation for Clinical Research. 2018 Aug [PubMed PMID: 29760160]|