Legionnaires’ disease: Controlling the hazard

Legionnaires’ disease – Not everyone who is exposed to the legionella bacteria will develop legionnaires’ disease, but every case of legionnaires’ disease is the result of exposure to the bacteria, and in almost every recorded case of legionnaires’ disease, the illness has resulted from exposure to a contaminated building water system, either plumbing or HVAC in nature.

“When the bacteria enter building water systems, they often find environments that are conducive to growth: warm water, stagnant water, or slow-moving water,” explains William McCoy, chief technology officer at Phigenics, and chair of ASHRAE’s Standard 188P committee. “Premise plumbing or building water system plumbing provides many opportunities for the bacteria to amplify.”

Amplifiers could come in the form of cooling towers and evaporative condensers, humidifiers, potable water heaters and holding tanks, pipes containing stagnant warm water, showerheads, faucet aerators, jetted bathtubs, pools, and public fountains.

The proposed ASHRAE Standard 188P, which is expected to be pub lished in final form early next year, is a voluntary practice standard that requires facility manager s and owners to formally take responsibility for controlling legionella in their building or water system.

“We know how to analyze and control this hazard,” says McCoy. “We need a standardized practice to specify for facility managers and owners exactly what to do in their facilities to control the hazard in a systematic and scientif ically defensible way.”

Disease outcomes

“The term legionnaires’ disease is the common name for a very serious form of pneumonia,” says McCoy. “It is an extraordinarily aggressive infection that causes a severe pneumonia. Any time a person is infected by legionella bacteria, they have legionellosis, but legionnaires’ disease is an infection that leads to pneumonia.”

The disease proves to be fatal in between five and 30 per cent of cases, with the mortality rate often depending on the speed at which treatment can be administered. Those who survive may not fully recover, suffering from irreparable lung damage. “Many people who endure those symptoms and survive have long- term debilitation,” reports McCoy.

The other clinical illness caused by the legionella bacteria is Pontiac fever. This is a flu-like illness without pneumonia. Persons with Pontiac fever experience fever and muscle aches without pneumonia, and generally recover in less than a week, without treatment.

Reducing the hazard

“In the case of legionellosis, the risk cannot be measured because it is too complicated. Transmission can var y, susceptibility varies, and all the various factors make it impossible to measure the risk. If you cannot measure the risk, by definition you cannot minimize it,” clarifies McCoy.

What can be done, he says, is to use practices that will control, reduce or eliminate the hazard that can lead to illness.

Growing conditions

While legionnella bacteria are commonly found in nature, they rarely pose a threat in the environment because the concentration tends to be very low. Like most bacteria, however, under certain conditions they can replicate to form sizeable colonies.

Legionella pneumophila can grow in tap water between 25°C and 42°C, with an optimal temperature for growth of 37°C (98.6°F). Standing water in cooling towers, humidifiers and other building systems can provide these conditions.

But there’s more to the spread of illness than bacterial colonies. “It is not just about the number of bacteria, it is also about the transmission of the bacteria. In a natural environment, often the numbers are very low, and there isn’t a ready source of exposure to aerosol,” explains McCoy.

“The only way that the disease can be transmitted is from the water, through the air, and into the lungs. You cannot get legionellosis from person-to- person. You cannot get legionellosis from drinking contaminated water, nor can you get legionellosis from skin exposure to contaminated water. You can only get legionellosis if you inhale the water.”

That’s why disease outbreaks tend to be tied to HVAC systems. Once a bacterial colony is present in a cooling tower or humidifier, the bacteria can become airborne by way of the ducts and fans in the HVAC system.

Decontaminating systems

The emergency protocol for decontaminating wet-type- heat rejection systems usually involves the use of chlorine and dispersants, which help increase the efficiency of biocides. For systems with significant legionella problems, a residual of as much as 3 ppm free chlorine may be used, but this level of chlorine can compromise piping systems if used on an ongoing basis.

When decontaminating a potable water system, the bacteria can generally be effectively controlled by increasing water temperatures to above 60°C.

Cooling tower cited in outbreak

The outbreak of legionnaires’ disease in Quebec City last year has been linked to an HVAC system in the city’s lower-town area. More than 180 cases of the disease were attributed to the outbreak, which started in the summer, and caused more than a dozen deaths.

Authorities in the city mandated that cooling towers in the affected area be inspected and cleaned, which helped bring the illness under control. More than 100 cooling systems were disinfected as part of the clean-up.

Making use of the standard

For compliance with ASHRAE Standard 188P, Prevention of Legionellosis Associated with Building Water Systems, building owners and managers need to take proactive steps to ensure that structures are in place to address the hazard.

“The first thing that must be done is to establish a team,” says Standard 188P committee chair William McCoy.

That team will analyze the building’s water systems, creating a schematic specific to the facility that identifies critical control points – areas most at risk of bacterial growth – and prescribed steps that will structure how those points in the system will be monitored, and what corrective action will be taken if the bacterial count exceeds the set critical limit.

The team must also verify that the plan is being implemented, and have a structure in place to verify that hazard control has been effective.

By Adam Freill

 

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