What are the most common organisms that cause septic arthritis?

Most Common Organisms Causing Septic Arthritis

Staphylococcus aureus is the most common pathogen causing septic arthritis across all age groups, accounting for approximately 40-45% of cases. 1, 2

Common Causative Organisms by Frequency

• Staphylococcus aureus: Most frequent pathogen (39-45% of cases), with methicillin-resistant S. aureus (MRSA) accounting for approximately 8% of septic arthritis cases 1, 3
• Streptococcus species: Second most common cause (15% of cases), including beta-hemolytic streptococci 1, 3
• Gram-negative bacteria: Less common but significant pathogens including:
  • Escherichia coli (4-10% of cases) 3
  • Pseudomonas aeruginosa (particularly in immunocompromised patients) 4
  • Kingella kingae (most common in children under 4 years of age) 5
• Other pathogens:
  • Neisseria gonorrhoeae (particularly in sexually active young adults) 6
  • Staphylococcus epidermidis (3% of cases, more common in prosthetic joint infections) 3
  • Haemophilus influenzae 4
  • Borrelia burgdorferi (3% of cases, cause of Lyme arthritis) 3

Age-Specific Considerations

• Neonates: Group B streptococcus is a common pathogen 5
• Children under 4 years: Kingella kingae is particularly prevalent 5
• Adults: S. aureus and streptococci predominate 1
• Elderly: Higher rates of gram-negative infections and potentially more resistant organisms 1

Special Clinical Scenarios

• Sickle cell disease: Salmonella species are common pathogens 5
• Intravenous drug use: Higher risk for S. aureus (including MRSA) and Pseudomonas infections 5, 4
• Prosthetic joint infections: Staphylococcus epidermidis and other coagulase-negative staphylococci are more common 7
• Human or animal bites: Consider Pasteurella multocida and Eikenella corrodens 4
• Immunocompromised hosts: Broader spectrum of pathogens including gram-negative bacteria and fungi 6

Clinical Implications

• Empiric antibiotic coverage should target S. aureus as the most likely pathogen 8
• Consider MRSA coverage (e.g., vancomycin) in high-risk patients or areas with high MRSA prevalence 8
• For children under 4 years, ensure coverage for Kingella kingae 8
• In patients with sickle cell disease, include coverage for Salmonella species 5
• Polymicrobial infections may occur in specific clinical scenarios (e.g., penetrating trauma, immunocompromised hosts) 8

Diagnostic Considerations

• Joint aspiration with synovial fluid culture remains the gold standard for diagnosis 8
• Synovial fluid culture is positive in approximately 80% of non-gonococcal septic arthritis cases 8
• Blood cultures should be obtained as hematogenous spread is the most common route of infection 5
• Consider specialized culture techniques or molecular methods for fastidious organisms like Kingella kingae 7

Treatment Implications

• Immediate surgical drainage combined with appropriate antibiotics is essential 8, 3
• The number of required surgical procedures and treatment efficacy depends on the initial stage of infection 3
• Delayed diagnosis or treatment is associated with poor outcomes and joint destruction 4, 2
• MRSA infections may require longer antibiotic duration and are associated with more complications 2