Condé Nast Traveler and "Dr. Germ" check in to three hotels—from ultra-budget to ultra-luxury—to see if the most expensive digs really are the cleanest. Christian L. Wright reports

Slip a freshly encoded key card into your hotel room door. A little green light comes on. Depress the handle. Like any other guest, enter the luxury sanctum with your suitcase, your laptop, and the assumption that the room is spotless, pure. Hotels—whether towers of luxury or roadside rests for the weary—suspend reality (at least for a while), keep secrets, and wipe the slate clean. Leave it to country-western singers to ponder who's been there before. The rest of us would rather not think about it. Yet every time we turn around, there's cause for pause: the recent viral outbreaks on cruise ships, the resurgence of bedbugs in even the poshest suites, the isolated cases of Legionnaires' disease associated with potable water in U.S. hotels, and new viruses arriving from distant shores.

Eighty percent of all infectious diseases are transmitted by contact, direct or indirect. Kissing, for example, is direct. Indirect? The doorknob you grabbed hold of to enter the hotel room, for one; the phone used to call down to room service for champagne and finger sandwiches, for another. These are the types of inanimate surfaces that can act like a guest book of germs (Staphylococcus aureus from Pathogen Park, USA…thanks for the memories!). The technical name for an object that can transmit disease is a fomite.

We more or less expect the city bus to be one great lumbering fomite, lurching from stop to stop. And public bathrooms might as well have a sign posted next to the soap dispenser, halfway between the paper towels and the cloudy mirror, that reads "These toilets were made possible with generous support from Fomite & Company, LLC." It is no wonder that Purell, the 62 percent ethyl alcohol hand sanitizer introduced in 1997, has been so successful, producing many imitators and now dangling off Bugaboo strollers. Contact with strangers is a dirty business. But surely a hotel room—particularly one that sets your wallet back more than $500 a night—rises above such pedestrian bother.

To find out, we got an audience with Philip M. Tierno, Jr., a.k.a. Dr. Germ, the microbiologist who helped solve the mystery of toxic shock syndrome and who was a member of Rudy Giuliani's task force on bioterrorism just after 9/11. "There are more germs in the human body than there are men who have ever walked the earth," says Tierno, shortly after the average person would be getting to "how do you do." "We could not live without these germs, but we can become very sick when our relationship with them is thrown out of balance."