Identifying Legionella risks for workers

Legionella can be fatal if it enters a building’s water system or other water-related areas.

Legionella can pose a fatal health risk when it gets into a building’s water system. (Photo: Shutterstock)

Six employees of an electrical company came down with flu-like symptoms after working in a client facility by the pier. The building’s sprinkler system had accidentally discharged while the employees were working inside.

Three went to their primary care provider where they were diagnosed with Legionnaires’ disease or Pontiac fever. However, none of the employees were diagnosed with pneumonia. All six employees fully recovered after three to five days.

The landlord of the building was notified and Legionella sampling was performed. The results showed Legionella Pneumophila Serogroup 1 (LP1) in a majority of potable water taps tested. This is the same strain that may cause Legionella Disease (LD), a potentially fatal pneumonia. The information was shared with the employer, who chose not to accept any future work involving this worksite due to the client’s lack of proper remediation of the worksite and the risk of exposing employees to LD with potentially fatal consequences.

Legionella can pose a fatal health risk when it gets into a building water system. The exposure pathway is by inhalation of aerosolized Legionella contaminated water droplets. Exposure can affect occupants, employees, facilities maintenance personnel, visitors and specialty vendors working around sources, which can aerosolize the contaminated water, including faucet aerators and touchless electronic eye faucets. Various guidances dictate the building owner as the responsible party for the control of Legionella bacteria in the building water system and connected equipment.

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Legionnaires’ disease

Legionella bacteria are ubiquitous in nature and are commonly found in natural aquatic environments such as streams, rivers, ponds, lakes and thermal pools, in moist soil and mud, and on the canopies of rain forests. Specific strains of the species Legionella pneumophila (LP) have been known to cause Legionnaires’ disease (LD). LD can be nosocomial (hospital-acquired or HAP), community-acquired (CAP) or travel-related. A likely source of Legionella infection includes potable water systems that become exposed to Legionella or colonized by the microorganism via municipal water systems.

Legionella can be found in public water distribution systems because it is able to survive routine water disinfectant treatment. Logically, because buildings and new water pipes are not built with Legionella in place, public water distribution systems are the likely inoculating sources of bacteria introduced into premise (building or facility) plumbing systems. Legionella can travel through a premise plumbing system and be exposed to humans or be trapped in areas where colonization and amplification may occur, which is a formula for future problems.

Additionally, biofilms (thick films of bacteria and other microbes that adhere to a surface) and other build-ups that inherently develop within the water pipes of both public (pre-premise) and premise water distribution systems. These biofilms can harbor and even protect Legionella from harsh environments, including attempts to control it through typical biocide applications. As a result, even if desired biocide levels are achieved, they may be ineffective in controlling Legionella bacteria. This is especially true if the system is repeatedly challenged by incoming contaminated public water or biofilm.

Water temperature is a critical factor for Legionella bacteria to be able to thrive in either natural or manmade sources. The temperature range for growth of Legionella bacteria is 68 – 122°F (20 – 50°C). Temperatures over 130°F will start killing Legionella, and at temperatures over 160°F, the bacteria will die instantly.

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Legionella dangers

Additionally, construction, disturbances or other activities in the public water system can cause physical disruptions that in turn may dislodge debris, scale, biofilm and Legionella into the incoming water, potentially causing ideal conditions for human Legionella exposure or introduction of Legionella into premise plumbing systems.

In humans, Legionella can cause either LD, which is a pneumonia with multisystem disease, or Pontiac Fever, which is a flu-like illness that will run its course without medical intervention.  While Pontiac Fever does not require treatment, LD causes death in 10-30% of cases, depending on the population affected. Together, LD and Pontiac Fever are called Legionellosis.

According to the CDC, it is not possible to distinguish LD from other types of pneumonia purely via clinical examination or x-rays. As a result, laboratory confirmation is essential for diagnosis. Urinary antigen testing is often used as a convenient and rapid means of diagnosing (presumptively) an LD case. However, the older culture methods, e.g., the isolation of Legionella from respiratory secretions, lung tissue, pleural fluid, or a normally sterile site is still an important method for diagnosis, despite the convenience and specificity of urinary antigen testing.

Investigations of outbreaks of LD depend on comparing both clinical and environmental isolates. Like swabbing DNA at a crime scene and comparing it with that of a potential suspect (exposure source), clinical and environmental isolates can be compared using monoclonal antibody and other molecular techniques. Because Legionella is commonly found in the environment, clinical isolates (like with a crime scene or victim DNA) are necessary to interpret the findings of an environmental (suspected source) investigation.

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Legionnaires’ disease can be hospital or community acquired, or even travel related. (Photo: Shutterstock)

Who’s at risk?

Risk factors thought to increase susceptibility to LD include:

Potential sources for Legionella exposure are routinely encountered and include:

Health-related consequences of LD

In a second case, an employee of an industrial plant was admitted to the ICU with Legionnaires’ disease with severe symptoms. He spent more than 30 days intubated and hospitalized, and experienced cardiovascular collapse, a heart attack, kidney failure and a stroke. He survived with residual kidney failure and neurologic deficits, requiring extensive rehabilitation.

The industrial cooling tower (CT) in the plant was the initial location of concern because Legionella had been previously identified there despite proper maintenance and disinfectant controls. Because of the current possible workplace-related LD, repeated CT water samples were obtained using a scientific exposure assessment study design.

Additionally, a history of alternative exposure sources revealed a recent family beach vacation for the affected employee within two weeks (incubation period) of their onset of illness, which included hotel stays during travel to and from the beach resort. Obtaining the vacation history was critical because approximately 20% of Legionnaires cases are travel-related, and this information helps in determining epidemiology and the causation analysis.

Using the latest DNA/genomic technology, Whole Genome Sequencing (WGS), none of the CT samples matched any of the LP organisms obtained from the sick employee. However, even though WGS is a very precise test, it is only one piece of the analysis. In order to be able to scientifically conclude with a high degree of confidence that the source of an LP organism has been identified, the laboratory findings must coordinate with the patient’s clinical information, the history of the disease development and the environmental samples. This is referred to as a proper causation methodology. In this case, a coordinated analysis of these factors led to the conclusion that there was no evidence to support that the employee’s illness was caused by the workplace.

Because of the risk to workers, the impact on business interruption and other general liability issues, vigilance, awareness and monitoring for the prevention of Legionella amplification in a building’s potable water system, water circulating equipment and water features will likely be required or expected to keep occupants and workers safe in buildings with these issues. Building owners should develop a formal water management program utilizing risk management guidance and principles to reduce the risk of legionellosis associated with building water systems.

Hung Cheung, MD, MPH, FACOEM, (solutions@cogencyteam.com) teaches environmental health and risk assessment to the junior residents at University of Pennsylvania Perelman School of Medicine where he is an adjunct assistant professor. He is president of Cogency Environmental, LLC, a consulting firm that investigates environmental injuries, occupational hazards, toxins related epidemiology studies and causation assessments using sound proven scientific methods.

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