Which of the following describes reactive arthritis?

Reactive arthritis is characterized primarily as an inflammatory arthritis that develops in response to an infection elsewhere in the body, most commonly following a genitourinary or gastrointestinal infection. It often occurs in large joints, such as the knees and ankles, and is typically a transient condition that resolves as the underlying infection is treated or clears on its own.

In this context, while it is important to recognize the other choices, the defining feature of reactive arthritis is its inflammatory nature and association with previous infections, focusing on large joints. Chronic autoimmune diseases, such as rheumatoid arthritis, differ significantly as they have a distinct pathophysiology involving persistent inflammation without a preceding infection. Degenerative joint diseases, like osteoarthritis, are related to joint wear and tear rather than inflammatory responses to infection. Lastly, while viral illnesses can lead to various types of arthritis, reactive arthritis is specifically not classified under the viral arthritis umbrella but is a reaction to infections, hence its unique definition.