Infection is usually caused by bacteria, occasionally fungal
Risk factors
Immunocompromised patients
Patients with chronic disease
Elderly
Young
Causative organisms
Newborns (<4 months) - S. aureus, Enterobacter sp., and group A and B Strep
Children (4 months to 4 years) - S. aureus, group A Strep, H. influenzae, Enterobacter sp.
Children/adolescents (4 years to adult) - S. aureus (80%), group A Strep, H. influenzae, and Enterobacter sp.
Adult - S. aureus, occasionally Enterobacter or Streptococcus sp
Sickle cell anaemia patients - S. aureus the most common, Salmonella species common and fairly unique to sickle cell patients
Pathophysiology
Routes of infection
Haematogenous - infection travelled in the blood from another infected site e.g. cellulitis, PWIDs, central lines/dialysis
Most commonly due to a single pathogen
Common localisation:
Children - long bone metaphysis
Adults - vertebral involvement is the most common
Exogenous - post-traumatic or contiguous spread
Post-traumatic - following deep injury e.g. open fractures
Contiguous spread - spread of infection from adjacent tissue e.g. injuries, secondary to infected foot ulcer in diabetic patients, secondary to pressure sore in elderly patients