U.S. airlines are scrambling to calm jittery passengers and investors while addressing growing public health concerns as the swine flu outbreak moves north of the Mexican border.

Travel to Mexico typically tails off this time of the year, a factor that may help officials contain the outbreak within the U.S., where relatively few cases and no deaths have been reported, as yet.

But for carriers, the bigger concern is that airline passengers may stop traveling within the U.S. and to other overseas countries if the number of cases reported continues to rise rapidly.

The worst-case scenario? Fearful passengers would stay home in droves, prompting a huge drop in air travel similar to the fall-off that surrounded the SARS epidemic in 2003. Offering shades of that earlier crisis, Hong Kong and Taiwan have warned that any passengers arriving with flu-like symptoms would be quarantined.

While the prospect of a major outbreak within the U.S. remains a distant threat, investors still fled airline stocks Monday. Shares of the six largest U.S. carriers were down between 9.4 percent and 17.4 percent in Monday training.

“I think there’s a general concern by investors that this may spread and you’d get a 2003-like SARS situation,” said Michael Derchin, airline analyst with FTN Midwest Securities Inc. “But it’s based more on panic right now than anything substantial.”

Such fears hit at a particularly inopportune time for large U.S. airlines, which were already struggling to attract recession-weary flyers. Analyst Kevin Crissey of investment bank UBS downgraded American, Continental, U.S. Airways and United Airlines on Monday over concerns that their second-quarter traffic was worse than anticipated.

Airlines say they’ve seen an uptick in calls from worried passengers, but relatively few cancellations as yet because of the swine flu. Most carriers also said they wouldn’t charge fees to customers who cancel trips to Mexico.

“We’ve had some calls to reservations from customers … but not huge numbers seeking changes or information so far,” said American Airlines spokesman Tim Smith.

American, United and Delta are among airlines are working closely with the Centers for Disease Control to monitor the situation and to develop a response if the threat worsens. But carriers said they weren’t actively screening passengers for flu symptoms, relying instead on airports in Mexico to conduct such checks.

United Airlines said that beginning Monday, it would send crews of cleaners swarming through airplanes returning from Mexico, swabbing every surface of the cabin with heavy disinfectants capable of killing viruses.

Such heavy cleans are typically done on United aircraft used for overseas flying about once every two weeks.

© 2009, Chicago Tribune. Source: McClatchy-Tribune Information Services.