Is MSSA Liver Abscess Common?
No, MSSA liver abscess is uncommon—Staphylococcus aureus (both MSSA and MRSA) accounts for only approximately 7-7.6% of all pyogenic liver abscesses, with the vast majority being polymicrobial or caused by enteric gram-negative organisms like E. coli and Klebsiella. 1, 2
Epidemiology and Prevalence
Pyogenic liver abscesses are predominantly polymicrobial or caused by enteric gram-negative bacteria (E. coli, Klebsiella pneumoniae), with Staphylococcus aureus representing a small minority of cases at approximately 7-7.6%. 3, 2
MSSA liver abscesses are "rarely reported" and "uncommonly encountered" in clinical practice, representing an unusual presentation even among the already uncommon category of staphylococcal liver infections. 1, 4
Within the subset of S. aureus liver abscesses, MRSA accounted for 7.6% in one retrospective series of 117 patients, suggesting MSSA would represent the remaining staphylococcal cases—still a small fraction of total liver abscesses. 2
Route of Infection and Risk Factors
Staphylococcus aureus liver abscesses typically result from hematogenous dissemination from another infected site rather than ascending biliary infection, which distinguishes them from the more common enteric bacterial abscesses. 2
The most frequent predisposing condition for MRSA liver abscesses is recent abdominal surgery, followed by biliary disease, suggesting healthcare-associated acquisition patterns. 2
Risk factors that should prompt consideration of staphylococcal etiology include: recent abdominal surgery, prolonged antibiotic use, history of skin abscesses, intravenous drug use, and healthcare contact. 4, 2
Clinical Implications
When a patient presents with severe illness and risk factors for S. aureus infection (healthcare contact, recent surgery, skin infections), clinicians must broaden empiric antibiotic coverage beyond standard gram-negative/anaerobic regimens to include gram-positive organisms. 1
Standard empiric therapy for pyogenic liver abscess (ceftriaxone plus metronidazole) does not adequately cover MSSA, necessitating addition of agents like nafcillin, oxacillin, or vancomycin when staphylococcal infection is suspected. 3, 1
Obtaining diagnostic aspiration with culture is critical to guide definitive therapy, as empiric regimens may miss uncommon pathogens like MSSA. 3, 1
Comparison to Common Causes
The most common pathogens in pyogenic liver abscess are E. coli and Klebsiella pneumoniae, which arise from biliary or intra-abdominal sources and account for the majority of cases. 3, 2
Other intra-abdominal infections and biliary diseases are the most common underlying causes of pyogenic liver abscesses, not hematogenous seeding from distant staphylococcal foci. 3