What is the most common cause of septic arthritis in otherwise healthy young adult patients?

The most common cause of septic arthritis in otherwise healthy young adult patients is gonococcus, which is the causative agent of gonorrhea, a sexually transmitted infection. This pathogen is particularly associated with joint infections in younger, sexually active individuals because it can disseminate from the genitourinary tract to the synovial membranes.

In young adults, sexually transmitted infections are more prevalent, and gonorrhea can lead to complications such as septic arthritis when it spreads into the bloodstream or directly into the joint space. Septic arthritis typically presents with acute joint pain, swelling, and fever, and in this demographic, the likelihood of gonococcal infection being the underlying cause is higher than other pathogens.

Other potential causes of septic arthritis, such as Staphylococcus aureus, while significant, are less common in this specific population compared to gonococcus. Escherichia coli is more associated with issues in older adults or those with certain risk factors. Streptococcus pneumoniae is primarily known for causing pneumonia and other respiratory infections rather than septic arthritis in healthy young individuals. Therefore, the association of gonococcus with the demographic factors of healthy young adults makes it the most frequent causative agent in this context.