Subacute (de Quervain's) thyroiditis is a rare but important cause of fever of unknown origin. Most cases of subacute thyroiditis are caused by a variety of viruses, for example, Coxsackie, cytomegalovirus, Epstein-Barr virus, and adenovirus. Influenza immunization or infection may cause subacute thyroiditis. We present the first reported case of a fever of unknown origin due to seasonal influenza A in a 67-year-old woman.

Subacute thyroiditis (SAT), also called de Quervain thyroiditis or granulomatous thyroiditis, is a self-limiting, possibly viral, and inflammatory thyroid disorder that is usually associated with thyroid pain and systemic symptoms. This report details a case of SAT possibly associated with influenza vaccine (Vaxigrip) in a young female. The diagnosis, therapeutic management and outcome are discussed.