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Sat 1 Apr, 2017 # Articles

Legionnaires Disease: A Primer For Defense Lawyers

With the recent Legionnaires disease outbreaks in New York, much attention has been focused on the nature of and causes of the disease. While outbreaks and cases are relatively rare, when they occur litigation often follows in hot pursuit. Here are several thoughts to help you successfully defend an action for damages alleging a case or an outbreak of Legionnaires  disease.

1. The Disease

Legionella pneumophila is a type of bacteria that thrives in warm and stagnant water. It was first identified by the Centers for Disease Control in 1977 after an outbreak caused 34 deaths at the 1976 American Legion Convention in Philadelphia. Legionnaires disease (also known as Legionellosis) generally occurs following inhalation of aerosolized water contaminated with the bacteria, resulting in a form of pneumonia. Legionella infections account for 1% to 5% of community-acquired pneumonia in the United States, comprising 17,000 to 23,000 cases annually.

There are currently more than 50 named legionella species, and about half of these have been associated with human disease. Legionella pneumophila is the species most frequently involved in human infections. And, while there are more than 15 serogroups of Legionella pneumophila, serogroup 1 accounts for the vast majority of Legionnaires disease cases. There are many sub-types among serogroup 1 of Legionella pneumophila. Identification of the species, serogroup, and sub-type is critical to associating a source of legionella with a case of Legionnaires disease.

2. Who gets the disease?

Legionnaires disease is opportunistic. It most frequently attacks individuals who are smokers, or who are immunocompromised, or who are over 60 years of age, or who are all or a combination of the above. Outbreaks are frequently seen in hospitals because that is where elderly immunocompromised smokers often congregate. Such cases are described in the literature as nosocomial Legionnaires  disease. It is likely that most individuals have had multiple exposures to legionella bacteria over the course of their lives, but have remained disease-free because they do not have any of these susceptibility factors.

3. Where is the bacteria?

Legionella pneumophila bacteria are distributed in and amplify in water systems. Water conditions that promote the growth of the bacteria include stagnation, water temperatures between 68º and 122ºF (95º to 115ºF is the optimal range), pH between 5.0 and 8.5, and availability of microorganisms such as algae, flavobacteria, and pseudomonas (which provide nutrition and harbor to the bacteria).

The most common and accepted sources for the bacteria are building cooling towers, building evaporative condensers, domestic hot water systems operating below 140ºF and delivering water to taps below 122ºF, humidifiers, decorative fountains that create water spray, spas, whirlpools, dental water lines, produce misters, and stagnant water in fire sprinkler systems.

4. How is legionella growth prevented or controlled?

The most prevalent legionella prevention method for cooling towers is chlorination. While many biocides have been used to try to control legionella growth, none has proved to be more effective than chlorine. While it is useful in controlling legionella growth, chlorine brings its own baggage to a water treatment scheme. In a cooling tower, levels of free residual chlorine above 1 ppm may be corrosive to metals in the systems or may damage wood used in a system. But if the free residual chlorine level is allowed to remain substantially below 1 ppm for a substantial period of time, legionella growth may not be adequately controlled. Any owners of property containing a cooling tower should retain a water treatment professional to develop and implement an appropriate water treatment program, and to periodically monitor the water once the treatment has been implemented.

In a domestic water system, there are different challenges. Lavatories, showers, drinking fountains, and water heaters have all been implicated as sources for legionella bacteria growth and aerosolization. The best way to avoid legionella growth in a domestic system is to store hot water at a minimum of 140ºF and deliver it to all outlets at a minimum of 122ºF. Also, the hot water tank should be drained periodically to remove scale and sediment and should be cleaned with a chlorine solution if possible. If a hot water system is suspected of containing legionella, it should be cleaned by raising the water temperature to a minimum of 158ºF for 24 hours and then flushing each outlet for 20 minutes.

5. There is no threshold dose for Legionnaires disease.

Most toxic tort practitioners are familiar with the concept of threshold dose from our work in chemical exposure cases. With most chemicals, the science has progressed to the point that scientists are in general agreement as to the dose of a particular exposure required to produce harm to a human system. There is no such dose known or established relative to legionella bacteria. The only current guidance is from OSHA, which has established guidelines to assess the effectiveness of water system maintenance and to interpret sampling results.

The OSHA guidelines — also known as Action Levels — propose that an employer take certain actions if the legionella content exceeds certain levels. OSHA Action Level 1 simply calls for cleaning followed by biocide treatment of a system, and it applies where the legionella content is above 100 colony-forming units per milliliter (cfu/ml) in a cooling tower, or above 10 cfu/ml in potable water, or above 1 cfu/ml in a humidifier or mister. OSHA Action Level 2 also calls for cleaning or biocide treatment, and further requires that immediate steps be taken to prevent employee exposure. OSHA’s Action Level 2 kicks in at 1,000 cfu/ml for cooling towers, 100 cfu/ml in potable water, and 10 cfu/ml in humidifiers and misters.

While the foregoing is certainly OSHA’s best judgment as to how to prevent harmful employee exposures to legionella bacteria, there is no assurance that an exposure to aerosolized water vapor containing legionella bacteria at levels below Action Level 1 will not produce Legionnaires disease. It is not yet certain whether the amount of the dose or the level of susceptibility of an individual is the more important factor in Legionnaires disease cases.

6. There is a new standard of care

This summer the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE), together with the American National Standards Institute’s Board of Standards Review (ANSI BSR) approved ASHRAE Standard 188—2015, titled Legionellosis: Risk Management for Building Water Systems. The standard establishes a national standard of care relative to legionellosis risk management in water systems in certain defined buildings. It is intended for use by building owners, managers, and those involved in the design, construction, installation, operation, maintenance, and servicing of centralized building water systems and components.

Standard 188—2015 requires certain facilities to create a Program Team and to implement a Water Management Program, including a document setting forth certain components and legionella control measures. Such a program is required for healthcare buildings, nursing homes, buildings taller than ten stories, and buildings containing multiple residential units served by a centralized water system. It is designed to reach buildings containing cooling towers, evaporative condensers, hot tubs, ornamental fountains, misters, atomizers, air washers, humidifiers, or any devices that release water droplets. It remains to be seen whether the adoption of the standard will have any appreciable effect upon the incidence of Legionnaires  disease,

7. There is a big difference between an outbreak and a case

An outbreak of Legionnaires  disease is defined as two or more people becoming ill at the same place at about the same time, and in most such situations an investigation by the Centers for Disease Control will ensue. CDC has investigated outbreaks in hospitals, prisons, hotels, schools, and office buildings. In virtually every outbreak investigation it has determined the source of the outbreak. But when an isolated case is diagnosed, the source is often difficult, if not impossible, to pinpoint.

The difficulty in identifying a cause for a specific case is due to the multiple potential sources for an exposure to legionella bacteria described above. An individual goes in and out of buildings, residences, and open areas throughout the day; an exposure may occur anywhere. Simply finding one source to which the individual may have been exposed during the two to ten day incubation period does not establish causation. Since there are so many species, serotypes, and subtypes of legionella bacteria, a source cannot be confirmed conclusively without culture testing. That is, the DNA from the bacteria source must be compared to, and match, the DNA from the bacteria in the individual. Only if they match can a causal association be confirmed. As might be expected, many experts on the plaintiff’s side are willing to ignore this gold standard causation evaluation method, and to opine that a causal association exists based on alternate testing that is far from conclusive.

8. How do you successfully defend a Legionnaires  disease case?

It obviously makes a big difference whether your client is being charged with causing an outbreak, or causing a case. If an outbreak is involved, it is critical to obtain the medical records of each individual whose cases make up the outbreak, and the CDC report identifying the source of the outbreak. If the identified source is one for which your client was responsible, and if there is no good basis upon which to challenge the CDC’s causal inference, then you must focus on the source and assess whether there existed a non-negligent explanation for the legionella growth at the source. Since legionella bacteria are ubiquitous in water distribution systems, if you can demonstrate that your client acted reasonably under the circumstances, or complied with ASHRAE Standard 188—2015, you may be able to persuade a fact-finder that it was the natural proliferation of legionella, rather than some misconduct by your client, that caused the outbreak.

The individual case is easier to defend. There usually will not be a CDC causal inference. Absent culture testing, there will be no conclusive evidence of the source of exposure. Most likely, there will have been multiple potential exposure sources during the two to ten day incubation period that cannot be ruled out as the source. For these reasons, in defending an individual case it is usually most helpful to focus on the potential sources, so that you can demonstrate to the fact-finder that there were multiple potential sources for the exposure that plaintiff cannot rule out. If the plaintiff has simply picked your client as the source he wants to present to the fact-finder without doing anything to rule out the other sources, you will have a very good chance to prevail in the case.


As long as there are water cooling towers and water distribution systems, there will be outbreaks and cases of Legionnaires  disease. Defense practitioners who study and understand the science are well on their way to a successful defense of a lawsuit filed after such an outbreak or case