Most Common Organism Causing Osteomyelitis
Staphylococcus aureus is the most common organism causing osteomyelitis across all age groups and clinical settings, responsible for approximately 50% of all cases. 1
Primary Pathogen Across All Patient Populations
S. aureus is the predominant pathogen in osteomyelitis, found in roughly 50% of cases regardless of the mechanism of infection (hematogenous, contiguous spread, or direct inoculation). 1, 2
This organism is particularly virulent in bone infection due to its ability to adhere to bone matrix proteins through Microbial Surface Components Recognizing Adhesive Matrix Molecules (MSCRAMMs) and form biofilms that resist both antibiotics and immune clearance. 3
S. aureus causes the majority of chronic osteomyelitis cases and is notoriously difficult to eradicate due to bacterial persistence mechanisms, including small-colony variant formation and intracellular reservoirs. 4, 5
Other Common Pathogens (Secondary Considerations)
After S. aureus, the frequency of other organisms varies by clinical context:
Coagulase-negative staphylococci account for approximately 25% of cases, particularly in prosthetic joint infections and hardware-associated osteomyelitis. 1
Aerobic streptococci are isolated in approximately 30% of cases. 1
Enterobacteriaceae (gram-negative organisms) are found in approximately 40% of cases, especially in diabetic foot osteomyelitis and pressure injury-related infections. 1
Age-Specific Pathogen Considerations
While S. aureus remains the most common organism across all pediatric age groups, certain populations require consideration of additional pathogens:
Neonates: Group B streptococcus is a common pathogen alongside S. aureus. 6, 1, 7
Children under 4 years: Kingella kingae should be strongly considered as it is frequently isolated in this age group. 6, 1, 7
Patients with sickle cell disease: Salmonella species are important pathogens that must be included in the differential diagnosis. 6, 1, 7
Special Clinical Scenarios
Polymicrobial Infections
Pressure injury-related osteomyelitis is typically polymicrobial, with an average of 3 aerobes and 1 anaerobe isolated from a single wound. 1
In this setting, S. aureus remains predominant (77.1% of cases), followed by Peptostreptococcus species (48.6%) and Bacteroides species (40%). 1
Diabetic Foot Osteomyelitis
S. aureus is still the most commonly isolated pathogen (approximately 50% of cases), but polymicrobial infections are common. 1
Coagulase-negative staphylococci, aerobic streptococci, and Enterobacteriaceae are frequently co-isolated. 1
Vertebral Osteomyelitis
S. aureus, streptococcal species, enteric bacteria, and other gram-negative rods are the most common pathogens. 1
In endemic regions, Mycobacterium tuberculosis and Brucella species must be considered. 1
Critical Clinical Pitfalls
Methicillin-resistant S. aureus (MRSA) is increasingly common, with up to 85% of S. aureus isolates from pressure injuries being methicillin-resistant in some settings. 1
Blood cultures are positive in only a minority of osteomyelitis cases, so negative blood cultures cannot rule out infection. 1
Bone biopsy remains the gold standard for definitive diagnosis and pathogen identification, as soft tissue or sinus tract cultures do not accurately reflect bone culture results. 1
The classic clinical triad of fever, pain, and diminished mobility is present in only approximately 50% of acute hematogenous osteomyelitis cases, making diagnosis challenging and often delayed. 6, 7