By Barry C. Fox, M.D., University of Wisconsin
Pneumonia, or infection of the lungs, is caused by a variety of agents. These may be bacteria or viruses in the air. But sometimes, the source of the infection, or even the way in which the infection reaches the lungs, is not very obvious. This is what happened in the very first recognized outbreak of what became known as Legionella, the cause of Legionnaire’s disease which causes pneumonia.
The Legionnaires
In 1976, hundreds of individuals at a convention in Philadelphia were struck down by a mysterious illness that at the time had no known cause, was not necessarily infectious, and had no name. Later it was named after the group at the convention—the American Legionnaires.
The convention had around 2000 members of the American Legion at the Bellevue-Stratford Hotel in Philadelphia, celebrating the country’s 200th birthday. What was unique about this population at risk was the large numbers of veterans who had been heavy cigarette smokers and had underlying emphysema lung disease. There were 182 reported cases, and 34 deaths.
The Spread of Illness
Although Legionella bacteria are present in most water systems at a low level, including your home, in 1976 it unfortunately became a dangerous situation because there was a lack of proper water quality maintenance at the hotel. This led to large numbers of bacteria being aerosolized.
Now, when others in Chicago who stayed at the same hotel started to report similar illnesses, an epidemiologic investigation was launched. This found that the fountain, locker rooms, swimming pool, and hot tub all tested positive for Legionella bacterium. This true incident actually resulted in 3 deaths.
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Identifying the Cause
At first, it wasn’t clear that the outbreak was actually due to an infectious agent. There were many possible causes of the illness, which included chemical exposures in the environment and toxic metal poisoning.
The bacterium, which was subsequently named Legionella pneumophila, did not grow on standard culture media. The Pennsylvania Health Department and CDC launched an intensive investigation. However, it wasn’t until 3 months later that the growth conditions for this ‘new’ bacterium were identified, and Legionella was found in abundance in the water cooling towers of the hotel, eventually seeding the air conditioning system.
Disinfecting for Legionella
Well, how worried should you be about acquiring this infection? Well, some pneumonia can be contracted by directly breathing in droplets contaminated with aerosolized bacteria. This is one reason that hotels, but especially hospitals, need to pay strict attention to water quality in showers, pools, air conditioning systems, and hot tubs.
Since the original outbreak, there have been over six hundred reported outbreaks of Legionnaires’ disease worldwide, even some that have originated inside hospitals. Hospitals and hotels are required to perform one of several types of disinfection for Legionella. Disinfection methods include chlorination, copper ionization, or more commonly ‘superheating’ water to 140 degrees Fahrenheit and, then, flushing the water storage tanks every month.
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Legionella in the Lungs
Now, let’s take a further look at how this germ, when aerosolized, can cause pneumonia. The mucous membranes of the throat and respiratory tract are very important in stopping inhaled substances from entering our lungs. However, if you have a chronic lung condition, or you smoke regularly, these membranes and attached cilia are damaged, and they can’t perform their innate immunity properly.
Legionella bacteria can then make their way deeper into the lungs and enter the alveoli, balloon-like structures, which help us exchange oxygen. The bacteria continue to multiply in the alveoli, causing pneumonia, an invasion of the alveoli and adjacent lung tissue.
Aspiration Studies
Now while failure of the respiratory defenses is common in individuals with underlying lung disease, you don’t need to have abnormal lungs to develop pneumonia. The common physiology of almost all pneumonia is what is known as aspiration from mouth, throat, and teeth bacteria, via gravity, into the lungs, and this has nothing to do with inhaling bacteria like Legionella. You’ll be surprised to know from studies done more than 30 years ago in medical students that half of us aspirate while we’re sleeping.
Investigators painted the back of the students’ throats with a harmless nuclear medicine tracer material. The students, then, slept on beds where there was an equivalent of an overhanging Geiger counter, and the investigators looked for the tracer in the students’ lungs. What prevented them from getting pneumonia was their normal ciliary clearance mechanisms of the upper and lower airways.
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The Prevalence of Legionella
Legionella bacteria actually live in harmony inside amoebae that are themselves harmless to humans. They are found in many aquatic systems, and they thrive at normal thermal temperatures, or even at water temperatures up to 110 degrees Fahrenheit. When inhaled in the lung, germs are captured by macrophages of our lungs, but are still able to live intracellularly in these immune cells. The pneumonia caused by Legionella tends to be more severe.
In 1976, the germ was originally thought to be a newly identified bacterium. Once the organism was cultivated, the CDC compared the bacteria with samples of an unknown illness from years past called Pontiac fever, from Pontiac, Michigan, and they found that the bacteria were identical.
Now while Legionnaires’ bacterium is of great historical interest, it is still one of the top five causes of bacterial pneumonia in the U.S., not from any outbreak situation, but because it’s ubiquitous in most water environments. Estimates of the disease in the United States are approximately 10,000 sporadic cases per year.
Legionella Detection
Infectious disease specialists have to maintain a high index of suspicion in patients presenting with more severe forms of community-based pneumonia. Now, fortunately, there is a urine test that can detect the equivalent of the shedding skin from the bacteria, which can detect around 80 percent of cases of Legionella cases.
However, there are some species that are not detected by this urine test. Also, since the germ does not routinely grow in the microbiology lab, and requires special media, the diagnosis has to be made clinically.
Common Questions About Legionella and Legionnaire’s Disease
In 1976, hundreds of individuals at a convention in Philadelphia were struck down by a mysterious illness that at the time was unknown. Later it was named after the group at the convention—the American Legionnaires.
Legionella bacteria actually live in harmony inside amoebae that are themselves harmless to humans. With improper water management, these bacteria can become aerosolized and can enter human lungs.
In 1976, the germ was originally thought to be a newly identified bacterium. Once the organism was cultivated, the CDC compared the bacteria with samples of an unknown illness from years past called Pontiac fever, from Pontiac, Michigan, and they found that the bacteria were identical.
There is a urine test that can detect the equivalent of the shedding skin from the bacteria, which can detect around 80 percent of Legionella cases.
