What are the common causes of osteomyelitis in children?

Common Causes of Osteomyelitis in Children

Staphylococcus aureus is the predominant causative organism of pediatric osteomyelitis across all age groups, with age-specific pathogens including Group B streptococcus in neonates, Kingella kingae in children under 4 years, and Salmonella species in patients with sickle cell disease. 1, 2, 3

Primary Bacterial Pathogens by Age Group

Neonates (Birth to 1 Month)

• Group B streptococcus is the predominant organism in this age group 1
• S. aureus remains an important pathogen even in neonates 3

Infants and Young Children (<4 Years)

• Kingella kingae should be strongly considered as a common pathogen in children under 4 years of age 1, 3
• S. aureus continues to be the most frequent overall cause 2, 3
• This age group accounts for half of all pediatric osteomyelitis cases, with children under 5 years representing the highest-risk population 2, 3

Older Children and Adolescents (≥4 Years)

• S. aureus predominates, responsible for the majority of acute hematogenous osteomyelitis cases 1, 3
• Streptococcal species are the second most common cause 1
• Methicillin-resistant S. aureus (MRSA) has emerged as a major pathogen, increasing from 6% to 31% of cases over recent years 4

Special Population Considerations

Patients with Sickle Cell Disease

• Salmonella species are important pathogens and must be considered in the differential diagnosis 1, 3
• These patients pose a diagnostic challenge because marrow infarction and osteomyelitis present similarly 2, 3

Immunocompromised Patients

• Polymicrobial infections and atypical organisms should be considered 1
• Fungi and mycobacteria become relevant pathogens in this population 1

Route of Infection

Hematogenous Seeding (Most Common)

• Hematogenous bacterial seeding is the most common cause of pediatric osteomyelitis 2
• Bacteria deposit in the highly vascular synovial membrane during bacteremia 1
• The metaphysis is the primary site of infection because looping nutrient vessels slow blood flow, creating an ideal environment for bacterial adherence and proliferation 3

Contiguous Spread

• Significant route particularly in neonates and infants from adjacent osteomyelitis 1
• Concomitant joint and bone infections occur in more than 50% of pediatric cases 1, 3

Age-Specific Vascular Anatomy

• In children ≤18 months, transphyseal vessels allow infection to spread from metaphysis directly into the epiphysis and adjacent joint space, explaining the high rate of concurrent septic arthritis 3
• Children under 2 years are more likely to develop septic arthritis than osteomyelitis due to these transphyseal vessels 2, 3

Emerging Pathogen: MRSA

MRSA has become increasingly prevalent and is associated with more severe disease:

• MRSA must be covered empirically with vancomycin 1
• MRSA infections demonstrate significantly greater inflammatory markers (ESR and CRP) on admission 4
• Patients with MRSA have increased length of hospital stay, prolonged antibiotic therapy, and higher overall complication rates compared to methicillin-sensitive S. aureus 4, 5
• MRSA produces more severe bone infection and requires more aggressive surgical and medical management 5

Critical Clinical Pitfalls

• The classic triad of fever, pain, and diminished mobility is present in only approximately 50% of acute hematogenous osteomyelitis cases, making diagnosis challenging 1, 3
• Negative blood cultures occur frequently, with bacterial isolates obtained in only 55% of cases 4
• Radiographs are often normal in acute osteomyelitis, as bone changes require 10-14 days to become visible 3
• Bacterial proliferation can cause irreversible cartilage damage within hours to days when joints are involved, necessitating immediate drainage and antibiotic therapy 1