Charleston International Airport’s status as a medium-size hub airport is being proven in a recent audit by the Charleston County Aviation Authority.

Despite increased competition from more airlines serving the airport thanks to Charleston being an international tourism hotspot as well as the home to a surging industrial market dominated by

Boeing, Mercedes-Benz and Volvo Cars, passenger counts are holding steady.

The state’s busiest airport features service from seven airlines — Alaska, American, Delta, Frontier (which started routes on Feb. 20), JetBlue, Southwest and United — with Allegiant joining the mix in April.

Charleston airport passenger traffic reached 3.98 million fliers over the past calendar year, nearly double its 2010 volume.

Columbia Metropolitan Airport, which has seen passenger counts drop as ticket prices rose, is trying to bring low-cost carriers back to the Midlands. Spirit and Allegiant are being targeted with incentive packages, including up to $500,000 in marketing, waivers for airport fees for two years, and the possibility of offer free ground handling.