Aetiology and assessment of liver abscess
Liver abscesses are usually bacterial (pyogenic) or amoebic.
In children, liver abscesses are rare and most commonly caused by streptococci or Staphylococcus aureusMishra, 2010Thavamani, 2020. Risk factors for liver abscess in children include hepatobiliary malignancies, liver transplant and biliary diseaseThavamani, 2020. Seek expert paediatric advice for management of liver abscess in children – it may be necessary to involve a multidisciplinary team, including a paediatric infectious diseases physician.
In adults, bacterial liver abscess can be a primary infection (eg caused by Klebsiella pneumoniae) or a secondary infection (eg following spread from an intra-abdominal source, such as diverticulitis or biliary tract infection, or seeding from a bacteraemia).
Spontaneous primary bacterial liver abscess is increasingly caused by K. pneumoniae, particularly among patients from Asia or those with diabetes. K. pneumoniae is usually the sole pathogen, and can be associated with metastatic infections such as endophthalmitis, meningitis, septic pulmonary embolismWang, 2022 and discitisWang, 2022.
Studies suggest an association between pyogenic liver abscess, especially those caused by K. pneumoniae, and colorectal cancerMohan, 2019. Consider a screening colonoscopy in patients with pyogenic liver abscess, especially those caused by K. pneumoniae.
Secondary infection is often polymicrobial, caused by aerobic and anaerobic bowel flora. Occasionally, an organism of the Streptococcus anginosus (milleri) group (S. anginosus, S. constellatus, S. intermedius) may be the sole pathogen.
In areas of northern Australia where Burkholderia pseudomallei is endemic1, liver abscess may be a clinical manifestation of melioidosis. If suspected, see Melioidosis for antibiotic therapy.
Amoebic liver abscess (caused by Entamoeba histolytica) most commonly occurs in travellers returned from an endemic country; however, it can also occur in individuals who have not travelled outside Australia.
The presentation of bacterial and amoebic liver abscess can be identical, so in all cases, take blood samples for culture and susceptibility testing (for bacterial causes) and serological testing (for E. histolytica). Ultrasound- or computed tomography (CT)–guided needle aspiration of the abscess, together with microbiological testing is usually necessary for diagnosis. If microscopy and bacterial culture results are negative, or if epidemiology and serology is suggestive, molecular testing for E. histolytica on the abscess fluid may be indicated. If radiological imaging suggests hydatid disease, needle aspiration should be delayed to avoid intraperitoneal spillage of hydatid contents – seek expert advice. See also Hydatid disease.