[International travelers Alicia Salinas, right, and her husband Genaro wear masks after arriving at Bush Intercontinental Airport on a flight from Mexico City Monday in Houston. AP photo]

Confirming 40 cases of swine flu in the U.S., the Obama administration said Monday it was responding aggressively as if the outbreak would spread into a full pandemic. Officials urged Americans against most travel to Mexico as the virus that began there spread to the United States and beyond.

More tips and resources:

Watch video: Obama says swine full cause for concern, not alarm

Photo gallery: See the flu's impact around the world

The Gradebook: Hillsborough schools tell students to cover up that sneeze

Map: Track the cases in U.S. and worldwide

CDC: Things you can do to prevent flu

Latest update: Cases in U.S.

How to: Plan and prepare