WASHINGTON (AP) -- Planes provide the quickest way to get from one part of the world to another -- for deadly contagious diseases as well as for people.In the spring of 2003, the respiratory virus SARS journeyed to five countries in 24 hours after emerging in rural China. Airline and tourism industries lost billions of dollars worldwide because people were afraid to travel and governments ordered flights canceled.With concerns about bird flu rising, U.S. health and aviation officials are taking steps to guard against a repeat.More quarantine stations have been set up at airports. A better system is in place for tracking travelers who might have been exposed. Flight crews have instructions to report sick passengers.Katherine Andrus, spokeswoman for the Air Transport Association, which represents major airlines, said the industry is concerned but doesn't want to overreact."We are taking all the appropriate measures to make sure that if it's a pandemic, we're prepared to respond," she said.Bird flu generally spreads to people through contact with bird excretions. The fear, though, is that it will mutate into a disease that spreads from human to human.The disease is most prevalent in Southeast Asia, to which only two U.S. airlines fly their own planes -- United and Northwest. But officials with the Centers for Disease Control and Prevention, airlines and U.S. aviation officials are keeping a close eye as the disease spreads elsewhere."The best thing we always do in these situations is stay in close touch with CDC and as soon as we hear something, we kick it out," said Steve van Beek, executive vice president of the Airports Council International, a trade group. By that he means letting airports know they should be prepared to make space available and tell staff and police that planes will need to be isolated and passengers quarantined.Since the September 11 terror attacks, most airports have contingency plans and crisis centers, van Beek said.Planes provide a good environment for spreading disease. Passengers are in close quarters and confined for hours, and multiple people may sit in the same seat between cleanings as the jet makes different stops.One way to limit the spread of disease is to force recirculated air through high-efficiency particulate filters, which trap fungi and germs. HEPA filters are used on about three-fourths of all commercial airplanes, Federal Aviation Administration spokeswoman Alison Duquette said."It's a standard industry practice for new aircraft," Duquette said.Airlines also follow CDC guidelines calling for flight crew to separate a passenger with a contagious disease, if possible, and provide a surgical mask. Pilots, by law, must notify the nearest quarantine station and quarantine workers will arrange for medical assistance, notify health departments and work with the airline to make sure the disease germs are killed, according to the CDC."Flu is pretty easy to kill with disinfectant," Andrus said.An Orlando, Florida, company called AeroClave has developed equipment that modifies temperature and humidity inside airplanes so the air kills smallpox, SARS and bird flu. A giant white box and hose pump heated air through an airplane's ventilation system for two hours, disinfecting parts of the plane that cleaning crews can't reach.Company founder Dr. Ronald Brown said the FAA is in the process of certifying the system."When we started this two and a half years ago, people looked at us cross-eyed," Brown said. "SARS was just our two-minute warning. It showed how things can spread rapidly."Brown said he's unaware of any standard for plane cleanliness. Airline cleaners wipe off stains and spills, and maintenance workers deep clean them during heavy maintenance checks, but Brown said he doesn't know of any airlines that disinfect seat belts, tray tables and overhead bins on a weekly basis.Since the SARS outbreak in 2003, the CDC has added nine more quarantine stations to international airports for a total of 17. CDC workers can meet airplanes from countries affected by a disease and isolate anyone who shows symptoms. They can also tell anyone possibly exposed what to watch for and how to seek help.Flight crews were reminded that they must notify health officials if a passenger shows suspicious symptoms. United Airlines spokeswoman Robin Urbanski said the airline has annual training for flight attendants on controlling infectious diseases and an airline doctor available around the clock.Passengers sometimes don't show disease symptoms while traveling but are diagnosed later. In those cases, the CDC tracks people who were exposed to the infected passenger.That turned out to be a challenge during the SARS epidemic, Andrus said, because so many people had to be contacted.The airlines and the CDC came up with a passenger locator card that can be read by a machine. The CDC would direct airlines to distribute the card, most likely on flights coming from the part of the world where the disease is endemic, Andrus said.Copyright 2005 The Associated Press. All rights reserved.This material may not be published, broadcast, rewritten, or redistributed.