Just in case you were so wrapped up with the NBA playoffs or the NFL draft that you didn’t watch much news over the weekend, or you didn’t read Jonathan’s note here that was posted last night — the reason your favorite airline stock is posting a loss this morning is directly attributable to one thing. Swine flu.

Or rather, fears that the flu, which has, up to now, been concentrated in areas of Mexico, but has already crossed the border to the U.S., has gone beyond the stage where cases that have been confirmed can be ‘contained.’

As a result, memories of the SARS epidemic of a few years ago, and what it did to the industry, (the Asian carriers were particularly hard hit) has investors selling off shares of airline stocks faster than you can buy a box of Kleenex.

The major airlines are taking the brunt of the selloff this morning, with shares of Continental, Delta, US Airways, United, Southwest, and American all down by double digits. Or very close to double digits.