Psittacosis presenting as a halo sign on high-resolution computed tomography

Psittacosis is an infectious disease caused by the intracellular microorganism Chlamydia psittaci, which mainly affects the respiratory tract. We described the high-resolution computed tomography findings in a 30-year-old man with psittacosis acquired by contact with psittacides. The diagnosis was confirmed by serological methods. High-resolution computed tomography showed nodular opacities surrounded by ground-glass attenuation (halo sign) in both lower lobes. Psittacosis should be considered in the differential diagnosis of pulmonary nodules with a halo sign in patients with a history of exposure to birds.