During the 2009 flu pandemic , many thousands of cases of ILI were reported in the media as suspected swine flu . Most were false alarms. A differential diagnosis of probable swine flu requires not only symptoms but also a high likelihood of swine flu due to the person's recent history. During the 2009 flu pandemic in the United States , the CDC advised physicians to "consider swine influenza infection in the differential diagnosis of patients with acute febrile respiratory illness who have either been in contact with persons with confirmed swine flu, or who were in one of the five . states that have reported swine flu cases or in Mexico during the 7 days preceding their illness onset."  A diagnosis of confirmed swine flu required laboratory testing of a respiratory sample (a simple nose and throat swab).