Some of the millions who travel to Saudi Arabia in November for the annual hajj will be greeted with face masks, hand sanitizer and fever checks as health officials strive to stem the spread of H1N1 swine flu during the world's largest pilgrimage.

The Saudi Health Ministry, aided by the U.S. Centers for Disease Control and Prevention, is setting up an emergency operations center to get real-time reports from area hospitals and clinics to track how many are sick, and will need the free anti-viral medication stockpiled for the dense gathering.

"It's an advance warning system," said the CDC's Dr. Shahul Ebrahim, who with Dr. Ziad Memish, the Saudi deputy health minister, outlined the planning and concerns Oct. 29 in the journal Science.

The hajj, a pilgrimage required of all able-bodied Muslims at least once in their life, attracts about 3 million people from 160 countries every year to the holy cities of Mecca and Medina.