- A doctor can perform laboratory tests that help identify the flu virus.

- Swine flu is presumptively diagnosed clinically by the patient's history of association with people known to have the disease and their symptoms listed.

- Usually, a quick test (for example, nasopharyngeal swab sample) is done to see if the patient is infected with influenza A or B virus.

- Most of the tests can distinguish between A and B types. The test can be negative (no flu infection) or positive for type A and B.

- If the test is positive for type B, the flu is not likely to be swine flu. If it is positive for type A, the person could have a conventional flu strain or swine flu.

- Swine flu is definitively diagnosed by identifying the particular antigens (surface proteins) associated with the virus type.