H1N1 (Swine Flu) Pneumonia

Chest radiograph shows patchy airspace opacities in bilateral mid to lower lung zones in a patient infected with H1N1 virus (lab confirmed), admitted to the ICU. Subsequent CT (not shown) reveals similar findings without pleural effusions or lymphadenopathy.

Facts

• First reported in Mexico in April 2009
• Fatality rate 0.45%
• Confirmed case = a person with an influenza-like illness with laboratory confirmed novel influenza A (H1N1) virus infection by one or more of the following tests: real-time RT-PCR, viral culture
• Influenza-like symptoms = fever, cough, sore throat, body aches, headache, chills, fatigue

Radiographic Appearance

• Initial exam is normal in nearly half of cases who had radiography
• When initial exam is abnormal, the abnormality is patchy consolidation (50%), groundglass opacity or groundglass opacity with consolidation (25%)
• Predominant location: lower lung zones (70%), diffuse (25%)
• Pleural effusion not common (less than 10%)
• Lymphadenopathy uncommon

Based on a single, uncontrolled study:

• Patients with abnormal initial radiograph were associated with admission and severe disease
• H1N1 infection was associated with a high rate of pulmonary embolism (36%) among patients admitted to the ICU

Reference:

Agarwal PP, Cinti S, Kazerooni EA. Chest radiographic and CT findings in novel swine-origin influenza A (H1N1) virus (S-OIV) infection. AJR 2009;193:1488-1493.