ABSTRACT
Septic arthritis is defined as a purulent infection in a joint cavity. The infection commonly
reaches the joint by hematogenous spread or by direct extension of pathogenic bacteria.
Microbiology
Staphylococcus aureus is a predominant etiologic agent of septic arthritis in all age groups.
A history to trauma often is associated with S. aureus infection (1,2). This organism is the cause
in over three-fourth of infected joints affected by rheumatoid arthritis. Neisseria gonorrhoeae is
themost frequent pathogen among younger sexually active individuals. Streptococcus spp., such
as Streptococcus viridans, Streptococcus pneumoniae, and group B streptococci, account for 20%
of cases. Aerobic gram-negative rods cause about 20% to 25% of cases. Most of these infections
occur in the very young or old, the immunosuppressed, and intravenous drug abusers (2).
In the newborn, however, group B beta-hemolytic streptococci and gram-negative enteric
organisms are also involved (1). Haemophilus influenzae type b, S. aureus, group A streptococci
and pneumoniae cause arthritis in children younger than five years of age. H. influenzae type b
infection is, however, now rare in immunized children (3,4). S. aureus and group A streptococci
are the most common causes of arthritis in children older than five years.
