Legionnaire's disease is a rare form of pneumonia, caused by inhalation of the Legionella bacteria. It is also possible, although less common, to acquire the disease through aspiration of contaminated water ("going down the wrong pipe.") The bacteria can contaminate the cooling towers of large air conditioning systems and hot water tanks, among many other areas, where it can spread through the inhalation of mist containing it. Legionnaires' disease is rare when compared with other forms of pneumonia. Just 20,000 cases take hold in the US annually - in contrast with over 3 million annual cases of pneumonia.
The disease, which is not contagious from person to person, is more likely to afflict adults over the age of 50 with compromised immune systems, a history of heavy tobacco use or chronic lung disease. Hospitals and nursing homes, in which we find a higher concentration of this demographic, must exercise particular care to ensure their hot water and cooling systems do not become contaminated with Legionella. No vaccine currently exists for Legionnaires', which can take hold in hospitals where it has a higher mortality rate than community-acquired infections - as many as 1 in 4 patients afflicted with a nosocomial (healthcare-acquired) case of Legionnaires' disease may succumb to the infection. Research indicates that the malady is more common during Summer and Fall.
The bacterium was named for the convention at which the first known outbreak occurred, the American Legion convention in Philadelphia in 1976. A number of attendees, aged 39 to 82, mysteriously died after the convention, complaining of fatigue, chest pains, fever and lung congestion. A Bloomsburg, Pennsylvania physician who independently treated three of the men noticed that attendance of the convention was a common thread between them. In total, 211 men were hospitalized with similar symptoms and ultimately 29 died of the mystery disease. Despite a prompt response by the Pennsylvania Health Department and CDC (who feared an outbreak of swine flu), nearly a year passed before Representative Joseph McDade of Pennsylvania's 10th Congressional District discovered that the previously identified bacteria, thought only to affect animals, had been breeding in the cooling tower of the hotel's AC system. It was later renamed Legionella pneumophila, after the Legion convention.
Causes of Legionnaires' Disease
Legionnaires' disease occurs when a host breathes in aerosolized water or soil contaminated with the bacterium. Less commonly, it may be acquired when contaminated water is aspirated (goes down the wrong pipe) where it could go on to infect the lungs. The disease has been characterized as the single greatest risk of waterborne disease in municipal water supplies. Due to their symbiotic relationship with certain microorganisms, Legionella is sometimes resistant to certain water disinfection techniques. If the hospital water supply is not properly maintained, contamination may occur. Other routes of transmission are exceptionally rare, with just one case of possible spread from patient to caregiver, and a handful of cases in which direct contact between contaminated water and a surgical wound caused infection. Legionella thrives between room temperature and 113 degrees. Optimum temperature for the growth of Legionella rests at 95 degrees.
Cooling towers, evaporative condensers of AC systems and hot water tanks are known environments in which the bacteria can thrive. Legionella pneumophila accounts for 90% of Legionnaires' cases, while its bacterial cousins L. longbeachae, L. feeleii, L. micdadei and L. anisa account for the other 10%. There are at least 180 identified strains of Legionella.
Other places the bacteria may dwell on hospital grounds include:
- evaporative coolers
- ice-making machines
- hot water systems
- water features and decorative fountains
- room-air humidifiers
- large plumbing systems
If contaminated water "goes down the wrong pipe" and into the trachea, infection is possible. Once inhaled or aspirated, the bacteria is consumed by macrophages in the lungs where they multiply, killing the macrophage (a kind of white blood cell.) Once the macrophage is killed, the bacteria burst from it and go on to infect more white blood cells.
Symptoms of Legionnaires' Disease
Symptoms begin to manifest two to ten days after exposure to the bacteria. Even for those directly exposed to the bacteria, only .1% to 5% will develop the disease. Incidence is greater in hospitals, where there are more likely to be immunocompromised individuals with a higher susceptibility.
General symptoms include:
- sputum (in half of the cases)
- coughing blood (in one-third of cases)
- muscle aches
- loss of appetite
- loss of coordination (ataxia)
- chest pain
Treatment for Legionnaires' Disease
There are a handful of antibiotics available to treat Legionella. Because of legionella's ability to reproduce inside the cell, any effective antibiotic must reliable intracellular penetration.
The most common antibiotics used to treat Legionella are:
Those with healthy immune systems have a far better recovery rate from Legionnaires'. Those who acquire the infection in a hospital (nosocomial infection), who may have compromised immune systems, tend to have a higher mortality rate. The earlier treatment with antibiotics begins, the greater chance a patient has at recovery. In recent years, mortality has plunged to just 5% as researchers have developed a better understanding of the bacteria's mechanism of infection. If treatment is delayed, there is a greatly increased risk of patient mortality.
While the general population seems to exhibit a hearty resistance to infection by Legionella, the same may not be said of patients of hospitals and nursing home who may have pre-existing conditions making them more susceptible to infection. In addition, they may be receiving treatments such as intubation, which put them at greatly increased risk for developing health care-associated infection by Legionella.
A patient is at increased risk if they receive:
- ventilation assistance
- other respiratory therapies
- corticosteroids or other immunosuppressive drugs
- solid organ transplants
Conditions which increase a patient's risk include
- chronic obstructive pulmonary disease
- head or neck cancer
- end-stage kidney disease
- conditions associated with heavy drinking or smoking
Proper maintenance of the hospital water supply is critical in the prevention of Legionnaires'. High-risk patients are advised to avoid exposure to tap water and to be provided sterile water for drinking purposes if Legionella is detected in the water supply.
To ensure legionella is not thriving in a hospital's water systems, environmental samples should be taken by swabbing areas of water flow, including faucets and shower heads and taking a bacterial culture.
Adherence to detailed and systematic water safety plans may greatly reduce the incidence of Legionella contamination in water systems. Water temperature should ideally be kept well below the point at which Legionella thrives, which is between 68 and 122 degrees. Water stagnation should be avoided, but should it become unavoidable (perhaps in the case of a hospital remodel or temporary closure of a wing), water systems ought to be thoroughly disinfected prior to resuming operations.
Methods to disinfect an entire water distribution system include:
- thermal (super heat and flush)
- hyperchlorination copper-silver ionization
Methods designed to disinfect a portion of a water distribution system include:
- ultraviolet light sterilization ozonation
- instantaneous steam heating
In order to completely eradicate Legionella colonies and prevent recolonization, it may be best to use a combination of these techniques.
The efficiency of various Legionella disinfection techniques is given in the table below.
|Method||Efficiency of Eradicating Legionella|
|Distillation or boiling||Excellent|
|Chlorination||Fair to good|
|Copper/silver ionization||Excellent (with limited evidence)|