Imaging is recommended because X-ray changes are common in the lungs of avian influenza A (H5N1) patients and can indicate the presence of pneumonia. This pneumonia tends to rapidly progress to respiratory distress and subsequent respiratory failure, and cases may die in spite of being ventilated.
This excerpt from a published article illustrates the progression of pneumonia in a hospitalized patient with avian influenza A (H5N1) infection. You can see the lung infiltrates worsen and become more dense from day 5 to day 10. However this severe pneumonia is not specific to avian influenza A (H5N1).