Most Common Organism for Joint Infection in Adults
Staphylococcus aureus is the most common organism causing joint infections in adults, followed closely by coagulase-negative Staphylococcus species (including S. epidermidis). 1, 2, 3
Native Joint Septic Arthritis
- S. aureus accounts for approximately 53% of native joint septic arthritis cases, making it the predominant pathogen across all joint types 3
- Methicillin-sensitive S. aureus (MSSA) is more common than methicillin-resistant S. aureus (MRSA), with MSSA representing 36% of cases compared to MRSA at 17.6% 2
- Coagulase-negative Staphylococci (CoNS) account for approximately 13% of native joint infections 2
- Group B Streptococcus represents 7.3% of cases and shows particular predilection for shoulder infections 2
Joint-Specific Patterns
- The knee is the most commonly affected joint (21% of cases), followed by shoulder and hip 2, 3
- MRSA is the leading causative organism specifically in shoulder septic arthritis, while MSSA predominates in knee and hip infections 2
- Small joint infections (particularly hand interphalangeal joints at 20%) have better outcomes than large joint infections but follow similar microbiological patterns 3
Prosthetic Joint Infections
- S. aureus and coagulase-negative Staphylococcus species are the most common organisms in prosthetic joint infections, with the distribution varying by infection timing 4, 1
- In acute prosthetic joint infections, S. aureus and S. epidermidis together account for 91.66% of cases 5
- CoNS (31.2%) slightly exceed S. aureus (28.8%) overall in prosthetic joint infections, particularly in hip replacements 6
- Among patients with S. aureus bacteremia who have prosthetic joints, 28% develop prosthetic joint infection, with knee arthroplasty carrying 3-fold higher risk than hip 7
Clinical Implications for Empiric Coverage
- Empiric antibiotic therapy for suspected joint infection must cover S. aureus, including MRSA coverage when risk factors are present (healthcare exposure, prior infection, injection drug use) 1, 2
- For shoulder infections specifically, MRSA coverage should be strongly considered given its predominance in this location 2
- Gram-negative organisms (Enterobacterales and non-fermenting bacilli) account for approximately 21.8% and 18.4% respectively of chronic prosthetic joint infections, requiring consideration in delayed presentations 5
Important Caveats
- Culture-negative joint infections occur in 60% of cases, often due to prior antibiotic administration, making empiric coverage decisions critical 3
- Withhold antibiotics for at least 2 weeks prior to joint aspiration when clinically feasible to maximize culture yield 1
- Polymicrobial infections occur in chronic prosthetic joint infections and should be considered when initial therapy fails 5