By Marc P. Weingarten

It seems all too obvious today, 40 years after the Legionnaires' disease outbreak in Philadelphia that led to the discovery of the eponymous Legionella bacteria.

We've learned Legionnaires' is transmitted when a person breathes in aerosolized water containing the bacteria. We've learned the bacteria can grow in whirlpool spas, misting equipment, cooling towers, showers, decorative fountains, and other places where water is circulated. And we've learned that people with compromised pulmonary systems - the elderly, smokers, and individuals with weakened immunological systems due to cancer or diabetes - are especially at risk.

The summer of '76 was an exciting time for Philadelphia. That summer marked the celebration of the nation's bicentennial and the triumphant release of Rocky. In addition, from July 21 to 24, 4,000 American Legion members from Pennsylvania held their annual convention in the city.

Soon after the convention's start, some Legionnaires began showing signs of an illness with symptoms resembling pneumonia. Over the next several weeks, the epidemic grew. Speculation abounded that it could be a strain of influenza, possibly swine flu. There were also concerns that it might be some sort of terrorist attack. Whatever the cause, a medical catastrophe was anticipated. Serious consideration was given to taking control of hospitals and imposing quarantines to prepare for an anticipated health Armageddon.

Early in the investigation, certain curious facts came to light. All fingers seemed to point to the Bellevue Stratford Hotel. Of the 4,000 convention attendees, 600 were staying at that hotel. Also, many convention meetings took place in the Bellevue's various meeting rooms. (Another curious piece of the puzzle was that people who spent time in the hotel lobby or on the sidewalk outside were at an increased risk of contracting the disease.) However, because there was no master list of attendees, medical investigators could not readily reach out to conventioneers for follow-up interviews.

Finally, after months of painstaking and often frustrating investigatory work, scientists from the Centers for Disease Control and the state determined the source of the bacteria to be the cooling towers on the roof of the hotel. A mist of water was believed to have escaped from the cooling towers and then drifted along the wall of the hotel down to the ground. This would explain the increased exposure and risk of people on the sidewalk outside the hotel. In addition, vents located near the base of the building brought air directly into the hotel lobby. This explained the increased exposure for people in the lobby.

There is a Latin saying, Ex malo bonum (Out of bad comes good). So what good came from this event in the summer of 1976, which saw more than 200 individuals sickened and 34 succumb to this disease?

The disease that will be forever linked to the American Legion convention at the Bellevue Stratford has led to changes in disease detection, prevention, and treatment that benefit us all. We now have the framework for better teamwork between laboratory scientists and epidemiologists. We also have the template for stronger cooperation and coordination among federal, state, and local health departments as well as 24/7 coverage for some agencies. We have seen more rigorous inspection codes as well as stronger sanitation techniques and climate control. And we have learned that the best way to prevent Legionnaires' disease is to keep water clean through the use of chemical agents or temperature control.

We also know that the disease is neither communicable nor contagious. But while it is readily treatable with antibiotics, there are as many as 8,000 to 18,000 new cases each year - many of which are misdiagnosed. Even now, with effective treatment, the fatality rate can be anywhere from 5 to 30 percent.

Despite advances in investigatory techniques, medical treatment, and engineering technology to guard against Legionnaires' disease, we still see periodic outbreaks. Last summer, more than 100 people became ill and numerous deaths resulted from a contaminated cooling tower in the South Bronx.

Legionnaires' is no longer a mystery, but vigilance must continue to prevent this disease from striking innocent victims in the future.

Marc P. Weingarten is a senior partner at Locks Law Firm in Philadelphia. mweingarten@lockslaw.com