What is the most common causative organism of septic arthritis?

Staphylococcus aureus is the most common causative organism of septic arthritis, particularly in adults. This bacterium is a part of the normal flora of the skin and mucous membranes, but it can become pathogenic under certain conditions, such as when there is disruption of the skin barrier, pre-existing joint conditions, or in individuals with compromised immune systems.

In cases of septic arthritis, Staphylococcus aureus is known for its ability to rapidly invade joint spaces, causing inflammation and significant damage. Its virulence factors, such as toxins and enzymes, enable it to persist and spread effectively within the synovial fluid of joints.

While other organisms may also cause septic arthritis, their prevalence is lower. For instance, Escherichia coli is more often associated with septic arthritis in certain populations, such as those with underlying urogenital infections or in specific demographic groups. Streptococcus pneumoniae is primarily linked to pneumonia and other systemic infections rather than to septic arthritis as a primary causative agent. Neisseria gonorrhoeae is more commonly associated with septic arthritis in the context of disseminated gonococcal infection, particularly in a younger sexually active population, but it is less prevalent overall compared to Staphylococcus aureus.