The most likely diagnosis is Mycobacterium tuberculosis infection of the hip. Joint infections with M. tuberculosis present as an indolent process, often in the hip, knee, or spine (Pott disease). Constitutional symptoms are frequently absent, and imaging may reveal nonspecific erosions that may be interpreted as osteoarthritis. Moderate elevation of the erythrocyte sedimentation rate is common. The diagnosis is made by joint aspiration with fluid sent for mycobacterial cultures. This patient is at increased risk due to origination from and travel to an endemic area (India) and the recent initiation of the tumor necrosis factor (TNF)-α inhibitor etanercept for treatment of rheumatoid arthritis. TNF-α inhibitors increase the risk of tuberculosis reactivation. Patients should be screened for latent infection prior to start of therapy and monitored for signs of infection during therapy. In this case, the patient had appropriate treatment for latent tuberculosis infection in the past but may have had an incomplete response or contracted another latent infection.

Gout rarely occurs in premenopausal women and typically presents in peripheral joints, with the great toe (podagra) the classic site of the first attack.

This patient is not sexually active and thus is not at risk for Neisseria gonorrhoeae infection. Furthermore, gonococcal arthritis typically spares the axial skeleton.

Rheumatoid arthritis (RA) is always a consideration in a patient with RA and joint pain. However, it is unusual for a single joint to be involved in an RA flare, and her arthritis appears well controlled overall. Isolated inflammation of a single joint out of proportion to other joints is a clue to infection.