A 57-year-old woman is hospitalized with high-grade fevers, chills, and right upper abdominal pain. The patient lives in Wisconsin and has no history of international travel. Her temperature is 40 C (104 F). Physical examination of the abdomen shows rebound tenderness. Laboratory studies show elevated aspartate and alanine aminotransferases. Imaging studies reveal a fluid-filled cavity within the right lobe of the liver as shown below.
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Which of the following microorganism/route combinations is most likely to be the cause of this patient's infection?
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The presence of a fluid-filled cavity in the liver in conjunction with fevers, chills, and right upper abdominal pain is suggestive of a hepatic abscess. In developing countries, hepatic abscesses have a relatively high incidence and are usually caused by parasitic infections (eg, Entamoeba histolytica, echinococcal). In contrast, hepatic abscesses are uncommon in the United States and are caused by bacterial infection in about 80% of cases.
Pyogenic bacteria can gain access to the liver through the following routes:
The types of organisms causing a hepatic abscess depend on the route of hepatic access. Systemic hematogenous seeding of the liver secondary to Staphylococcus aureus infection at a distant site is the most plausible choice of all the answer options.
(Choice A) Ascending cholangitis is usually caused by enteric gram-negative bacilli (eg, Escherichia coli, Klebsiella) and enterococci. Chlamydia trachomatis is transmitted sexually and is not found in the enteric environment.
(Choice B) Hepatic abscesses that arise by direct invasion from a nearby source are usually enteric gram-negative bacilli and enterococci. Cytomegalovirus can cause hepatitis in the immunosuppressed patient, but it is not associated with the development of a hepatic abscess.
(Choice C) Traumatic penetrating injuries to the abdomen (eg, stab wound) typically result in abscesses that contain mixed aerobic and anaerobic flora. Entamoeba histolytica is most often transmitted through foodborne exposure and in areas with poor sanitation. It can cause a hepatic abscess by ascending from the colon through the portal venous system.
(Choice E) Streptococcus pneumoniae colonizes the nasopharynx and typically causes disease within the respiratory tract region (eg, pneumonia, otitis media, sinusitis) and meningitis. However, hepatic abscesses due to portal vein seeding typically arise from abdominal infectious processes (eg, appendicitis, diverticulitis) and S pneumoniae is not an enteric pathogen.
Educational objective:
Staphylococcus aureus can cause hepatic abscesses via hematogenous seeding of the liver. Enteric bacteria (eg, Escherichia coli, Klebsiella, and enterococci) can cause hepatic abscesses by ascending the biliary tract (ie, ascending cholangitis), portal vein pyemia, or direct invasion from an adjacent area (eg, cholecystitis).