In 1976, a mysterious respiratory disease started affecting people who had attended an American Legion convention at a hotel in Philadelphia. After 221 people had gotten sick—34 fatally—the source of the infection was traced to a newly discovered bacterium that had created a colony in the air-conditioning system of the hotel where the convention had taken place. The bacterium, Legionella pneumophilia, had previously been regarded as unable to affect humans. Legionnaires’ disease is now considered an important public health concern, particularly in developing countries, where it is believed to be significantly under-diagnosed.
The bacterium thrives in wet environments, especially standing water. Mere exposure to the microbe, however, doesn’t inevitably lead to illness. Smokers are among those who are especially vulnerable, as with all lung diseases, and people with weakened immune systems—such as due to AIDS or to corticosteroid use for managing other illnesses—are as well. People over age 65 are also at risk. Other risk factors include chronic lung disease or being on anti-rejection drugs. In addition, people in certain jobs may have occupational exposure to the bacterium that makes infection more likely.
Although the disease is more common in the developing world, there are still occasional outbreaks elsewhere. In October, more than a dozen people in Alabama were determined to have the disease. This outbreak was traced to a nursing home in the town of Florence. Nursing homes are common sources of Legionnaires’ disease; in this instance, ten of the patients were residents of the home and the others, including one woman who died, were frequent visitors. Another outbreak in the Lehigh Valley area of Pennsylvania affected six people. That was attributed to a decorative fountain at a medical center.
The usual treatment for Legionnaires’ disease is with antibiotics. Treatment needs to be started promptly to have the greatest chance of being effective. The bacterium responsible for Legionnaires’ disease can sometimes also cause another, milder disease called Pontiac fever. Pontiac fever causes flu-like symptoms, but is almost entirely non-fatal, and generally goes away on its own.