Airlines suffered an 11.1 percent fall in passenger numbers in March year-on-year, and swine flu stands to compound financial problems and suppress traffic even more, an industry body said Tuesday.

"The global economic crisis continues to reduce demand for international air travel," the International Air Transport Association (IATA) said in a statement that warned the swine flu virus that has killed up to 149 people in Mexico could prove costly for airlines.

"Anything that shakes the confidence of passengers has a negative impact on the business. And the timing could not be worse given all of the other economic problems airlines are facing," it said.

Cargo traffic fell 21.4 percent last month compared to March 2008. Freight demand is a key barometer for the health of global trade, which has weakened considerably in response to the world's economic downturn and credit crisis.

IATA, which represents 230 airlines including British Airways, Cathay Pacific, United Airlines and Emirates, has said airlines would lose $4.7 billion this year as a result of the economic downturn that has kept people and cargo from flying.

Its traffic data excludes domestic flights.