WASHINGTON (AP) -- Some of the millions who travel to Saudi Arabia next month for the annual hajj will be greeted with face masks, hand sanitizer and fever checks as health officials strive to stem the spread of 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 Thursday in the journal Science.

The hajj, a pilgrimage required of all able-bodied Muslims at least once in their lifetime, attracts about 3 million people from 160 countries every year to the holy cities of Mecca and Medina. The climax is a four-day period during which people gather in and around Mecca to perform a series of rituals.

The density of the pilgrims, with shoulder-to-shoulder contact as they pray, provides "a perfect transmission atmosphere" for the new flu that scientists call the 2009 H1N1 strain, Ebrahim and Memish warned.

Saudi health officials during the summer urged that children, pregnant women, the elderly and those with chronic diseases postpone this year's trek, but they won't be banned.

"We need to be prepared" for expected outbreaks, Memish said in a telephone interview.

Among those preparations:

-Rapid reporting of illnesses from a network of hospitals and clinics back to the emergency operations center, where Saudi officials will work closely with U.S. flu specialists to rapidly diagnose cases and track whether the seriously ill are straining health systems.

-Saudi aid groups will donate personal hygiene kits to arriving pilgrims that contain face masks and hand sanitizer. But the report urged those protections during the trip, too. Alcohol-based hand gels are allowed under religious law since the alcohol is for a medical purpose, the report said -- but it cautioned that pilgrims may shun covering their faces.

-Thermal screening equipment to detect passengers with fevers are in place in Saudi airports, which are being advised to set aside room to hold 200 to 300 pilgrims for evaluation.

-Encouraging that pilgrims get vaccinated at least two weeks before departure if they live in a country that has some of the scarce vaccine supplies. China this week announced that its more than 12,000 planned hajj travelers will be inoculated.

Copyright 2009 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.