Legionnaires' disease

April 1, 2001
Last year, I became acutely aware of Legionnaires disease while researching the controversial issue of using water heaters for both potable water and hydronic systems. While I was familiar with the 1976 outbreak in Philadelphia, I was not well-informed about the disease itself or the bacteria that causes it. A wealth of information is available, and I have found the worlds leading authorities are

Last year, I became acutely aware of Legionnaire’s disease while researching the controversial issue of using water heaters for both potable water and hydronic systems. While I was familiar with the 1976 outbreak in Philadelphia, I was not well-informed about the disease itself or the bacteria that causes it.

A wealth of information is available, and I have found the world’s leading authorities are more than willing to share their knowledge.

In 1976, while attending an American Legion Convention at the Bellevue Stratford Hotel, 211 people became ill and 34 of them died from what was thought to be a previously unknown type of bacterial pneumonia. After this outbreak and identification of the bacterial strain, the Centers for Disease Control and Prevention examined some previously collected tissue samples, which revealed earlier cases of Legionnaire’s disease.

One was circa 1947 from a soldier who had developed and died of pneumonia while at Fort Bragg, N.C. Further study revealed an outbreak occurred in 1957 at a meat-packing plant.

Another form of infection caused by legionella bacteria is Pontiac Fever. Its name is derived from the first recorded outbreak in Pontiac, Mich., which affected 144 people at the Oakland County Health Department. Flu-like symptoms occur that last for several days.

So who is at risk? Generally speaking, elderly people with immune systems that are compromised by medication or illness; smokers; heavy drinkers; and aids, heart and kidney patients. Blood samples have shown that a large percentage of the population has been exposed to legionella bacterium. As many as 10,000 to 100,000 cases of Legionnaire’s disease occur each year (depends on whose statistics you believe), and some think those are low numbers. Unfortunately, many cases go unreported because they are simply listed as pneumonia. Penicillin, a drug often prescribed to pneumonia patients, is ineffective. Erythromycin is the proper medication.

"Amplifiers," a term often used with this issue, are devices capable of providing an environment suitable for the growth of legionella bacteria. Some examples include air conditioning cooling towers, potable water systems, humidifiers, whirlpool tubs, spas and domestic water heaters. Any device capable of creating a mist that can be inhaled (vegetable misters, shower heads, aerators) in an environment where people are present can deliver a potentially fatal dose if the bacteria are present in sufficient numbers to overwhelm the immune system. Human lungs are a virtually perfect environment for legionella bacteria.

Legionella bacteria need four very basic conditions to survive and grow:

Water temperatures between 68? and 122? F;

A pH between 5.0 and 8.5;

Biofilm (sediment); and


Biofilms are the slime and layer of junk we find in piping. Plumbing repairs can dislodge large amounts of infected biofilm.

Sediment occurs in tanks. In recent years, water heater manufacturers have cranked the thermostats down in order to stem the tide of scalding incidents and to increase efficiencies. Although legionella bacteria begin to die above 120? F, they don’t really get kicked in the pants until the temperature rises above 130? F.

The pH of nearly all potable water systems fall right in the most desirable range for growth. Stagnation is all that we’re really missing.

The hydronics industry is enjoying a radiant revolution. As more and more people discover the benefits, comfort and reliability of these products, the pressure has increased to find more economical installation methods. The temptation to cut corners and compromise consumer safety, knowingly or unknowingly, has given rise to cross-connecting potable water with hydronic loops while using a domestic water heater as the energy source. As my bride said, "Gross, that’s like drinking your own bath water!"

What happens when the hydronic system is at rest? Stagnation. Various code bodies and professional organizations want to see timers installed to exercise the system pump to prevent long-term stagnation, but like any mechanical device, they are subject to failure and no one is inspecting for code compliance in my neck of the woods.

Think chlorine is keeping your water safe from legionella bacteria? Think again. Chlorine levels in typical potable water systems are 10,000 times lower than the levels needed to suppress these bacteria cultures. High chlorine concentration flushes of infected systems do not eradicate the bacteria and they are typically back within just a few short weeks. Elevated levels of chlorine in potable water also create carcinogens. Chlorine dissipates in hot water, and some believe that this also contributes to pitting in copper tubing.

High-temperature water flushes (140? F and above) also offer only temporary suppression as has been documented in numerous locations. In several hospital cases, flushes using 180? F water for five minutes at every faucet were employed. Many man-hours were required, notices posted to warn people not to use the faucets during the flush period and equipment was taxed to its limits keeping up with the demand. Although notices were properly posted, several scalding cases occurred.

At present, there appear to be two effective methods for controlling legionella growth.

Ionization of copper and silver alloys in the potable water stream for commercial applications is gaining acceptance as a method of killing off the bacteria and preventing its return. These systems are becoming more popular and might eventually be available in residential models.

Maintaining higher water temperatures is the other method. Several other countries have adopted plumbing codes that require water temperatures to be maintained at or above 140? throughout the entire potable hot water distribution system and only allow a small amount of cooler water, typically 131? or above, after the mixing valve.

The only way to prevent legionellosis acquired via mechanical systems is to improve the design and maintenance of cooling towers and plumbing systems.

Legionellosis has 5%-20% fatality rate in general public exposures and a fatality rate as high as 40% in hospital-acquired cases. According to the cdc, only 5%-10% of estimated cases are reported.

Clearly our existing plumbing codes must be changed to disallow cross-connected potable and hydronic systems. Manufacturers of water heaters should increase the delivery temperatures, and plumbing codes should be changed with respect to requirements for mixing valves and scald-guard faucets. We should be prepared to accept and support these changes.

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