Nearly 40,000 Twin Cities residents will go to their mailboxes on Sunday, May 6, to find an unusual delivery: An empty pill bottle representing a powerful antibiotic that would be delivered in the event of a bioterrorism attack in Minnesota.

The exercise, dubbed "Operation Medicine Delivery," has united the Minnesota Department of Health with the U.S. Postal Service to answer questions that have plagued public health officials since the terror attacks of 9/11. What if an airborne anthrax attack struck the Twin Cities? How would millions of Minnesotans get the medicine to survive?

More than 300 mail carriers will participate in the test, fanning out across four neighborhoods in Minneapolis, St. Paul, Robbinsdale and Golden Valley. They plan to reach 37,000 households in four ZIP codes: 55101, 55102, 55411 and 55422.

The overall goal of the exercise would be to deliver preventive doses of medication to most people within the first 48 hours of a bioterror attack, though much of that would happen through local medicine dispensing sites run by area public health organizations. During an actual bioterror crisis, the couriers would be alerted through an automated phone message.

The exercise, funded through the U.S. Department of Health and Human Services and the Postal Service, will spark an intense period of evaluation, when health officials will finally see if the idea could work under the most catastrophic public health conditions.

The tactic has been tested on a smaller scale in Boston, Philadelphia and Seattle, but the Twin Cities experiment will be its first full-scale test.

Minnesota health officials have been developing the idea since 2004 and expect it to be closely watched by other states.

"We made it a priority," said Health Department spokesman Buddy Ferguson. "We really felt it was important to take the lead on this."

The average mail carrier reaches 400 households in a day, said Postal Service spokesman Pete Nowacki, so delivery "is the easy part."

But, he added, Postal Service volunteers had to go through hours of safety training and preparation --including being fitted with protective masks. Local law enforcement officials will be on hand to escort the postal workers, as they would be in a true emergency.

Mail carriers are enthusiastic about the experiment because they often "get to know people as more than just an address," Nowacki said. Many are deeply committed to the neighborhoods they serve, and at 6 a.m. on what would normally be a day off, their trucks will roll out.

The biggest logistical concern for the Health Department and the Postal Service has been informing the communities that will be part of the simulation. They're working through local public health organizations to notify residents in the affected ZIP codes to expect the delivery -- and to recycle the empty bottles.

Amanda Bankston is a University of Minnesota student on assignment for the Star Tribune.