NO ONE knows why, but in 1997 a mind contagion broke out in New Orleans. As the city geared up for its annual Mardi Gras festivities in January, a rumor began spreading via word-of-mouth, fax, and forwarded email to the effect that a highly organized crime ring in New Orleans was carrying out plans to drug visiting tourists, surgically remove healthy kidneys from their bodies, and sell the organs on the black market.

The viral message, which most often arrived under the header "Travelers Beware," sparked an avalanche of phone calls to local authorities, prompting the New Orleans Police Department to publish an official statement to calm public fears. Investigators found no substantiating evidence.

The story had a familiar ring. Before New Orleans, people said it happened in Houston; before Houston, Las Vegas — where an unsuspecting tourist was drugged in his hotel room by a prostitute and woke up the next morning, supposedly, in a bathtub full of ice, minus a kidney.

A chilling tale, and a dubious one

It's a scenario that has taken many forms. I first heard it myself many years ago from a friend who'd heard it from another friend, whose mother swore it had happened to a distant cousin.

In that version, the victim — we'll call him "Bob" — was on a business trip alone somewhere in Europe, and went out to a bar one night to have a cocktail. Wouldn't you know it, he woke up the next morning in an unfamiliar hotel room with severe pain in his lower back.

He was taken to the emergency room, where doctors determined that, unbeknownst to himself, Bob had undergone major surgery the night before. One of his kidneys had been removed, cleanly and professionally.

A chilling tale, and a dubious one. With minor variations, the same story has been told thousands of times by thousands of different people in many different locales. And it's always based, like the version I heard, and the version you heard, on third-, fourth-, or fifth-hand information.

It's an urban legend.

Which is not to say that human organs are never bought and sold illicitly in parts of the world where people can get away with it. The case for the existence of an international black market organ trade has become increasingly convincing in recent years. What remain unsubstantiated are the tales of "back room" organ thefts perpetrated in the dark of night in seedy hotel rooms or secluded alleyways.

"There is absolutely no evidence of such activity ever occurring in the U.S. or any other industrialized country," says the United Network for Organ Sharing. "While the tale sounds credible enough to some listeners, it has no basis in the reality of organ transplantation."

In fact, it's all but impossible for such activities to take place outside properly-equipped medical facilities, UNOS argues. The removal, transport, and transplantation of human organs involves procedures so complex and delicate, requiring a sterile setting, minute timing, and the support of so many highly-trained personnel, that they simply could not be accomplished "on the street," as it were.

No confirmed victims have ever come forward

The National Kidney Foundation has repeatedly issued requests for alleged victims of such crimes to come forward and validate their stories. To date, none have.

Even so, like so many urban legends fueled by irrational fear and ignorance, the organ theft story continues to spread from person to person and place to place, changing and adapting to its surroundings over time like a mutating virus.

Unlike many other urban legends, unfortunately, this one has put real people's lives at risk. A decade or so ago, rumors began spreading in Guatemala to the effect that Americans were kidnapping local children in order to harvest their organs for transplantation in the United States. In 1994, several U.S. citizens and Europeans were attacked by mobs who believed the rumors to be true. An American woman, Jane Weinstock, was severely beaten and remains critically impaired.