In the summer of 1976, physicians and hospitals across the country reported cases of pneumonia due to a previously unidentified bacterium. A productive cough and fever prompted chest X-rays, which typically showed pneumonia in both lower lobes of the lungs. Some patients became severely ill, requiring ventilator support. A small percent died.
Epidemic specialists swung into action, searching for common features among the patients. They were predominantly middle-age or older men, many of whom smoked, and had recently attended an American Legion convention in Philadelphia.
Clif CleavelandThe Bellevue Stratford Hotel served as headquarters for the meeting. All the victims had either roomed or attended sessions at the hotel. Convention-goers dispersed widely as they returned to their hometowns after the meeting. Some patients did not become ill until two weeks following their return.
By the time the outbreak subsided, 189 cases had been reported with 29 deaths from the infection. Many cases were likely never reported.
After exhaustive study, scientists identified a new bacterium in sputum samples or autopsy material obtained from victims of the outbreak. The bacterium was named Legionella and the associated illness was called Legionnaire's disease.
Even today, Legionella is difficult to grow in the lab, which can lead to delays in diagnosis. One strain of Legionella causes most of the related pneumonias. Although sensitive to several antibiotics, the organism can still cause devastating pneumonia in elderly people, smokers and people with impaired immunity or chronic lung diseases such as emphysema. Another strain causes a much milder respiratory illness.
An extensive search for the source of the 1976 epidemic led to reservoirs of water in the cooling towers for the air-conditioning system at the Bellevue Stratford. The system generated a fine, contaminated mist which was distributed throughout the hotel. Only a very small fraction of people exposed to the mist became ill.
In later years, bathroom showers and nebulizers were identified as other possible sources of Legionella contamination. Person-to-person spread of the microbe does not occur.
Scientists showed that, upon invading the body, the Legionella bacteria quickly enter specialized cells of the immune system. The intracellular location of the bacteria limits the effectiveness of antibiotics. An infected cell quickly becomes a site for rapid reproduction of the bacteria, which are released to infect other cells.
Once the causative organism was identified, other outbreaks were reported worldwide. Legionella had clearly existed in nature but had not previously been linked to human infection.
The most recent outbreak occurred this summer in the South Bronx in New York City. As of Aug. 15, 121 cases have been reported with 12 fatalities. Cooling towers on older buildings have once again been confirmed as sources of the infections.
Stimulated by this epidemic, officials in New York State imposed mandatory inspections of cooling towers to identify those that harbor Legionella. These must be immediately sterilized, and this precaution should be extended to all older air-conditioning systems that employ cooling towers.
Epidemics make headlines. Individual cases do not. Up to 18,000 cases of Legionella pneumonia are reported in the U.S. each year with an estimated 100 deaths. Improved reporting of cases may account for rising figures.
Legionella remains an infrequent cause of community-acquired pneumonia. Its diagnosis should prompt a search for a contaminated source of aerosolized water to avoid repeated outbreaks.
Contact Clif Cleaveland at cleaveland1000@comcast.net.