Taking a deeper look.

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, North Carolina. 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, Michigan, which affected 144 people at the Oakland County Health Department. Flu-like symptoms occur that last for several days.

“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 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.

Stats and conditions

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

Legionella bacteria are ubiquitous (meaning virtually everywhere) in our environment. According to the CDC, most people have been exposed to Legionella. The vast majority of people survive the exposure because they are relatively healthy, and the bacteria were not present in sufficient numbers to overwhelm their immune system. 

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. 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.

Legionella bacteria have specific needs to flourish. These conditions include:

  • Water temperature between 55° F and 133°, with 80° to 120° being most favorable for rampant reproduction; 
  • pH between 5.0 and 8.5, which pretty much encompasses our potable water system ranges;
  • Biofilms within potable or hydronic piping in open dual-use, cross-connected dual-use potable/hydronic systems and sediment in hot water tanks; and
  • Stagnation — any time the system is at rest.

Tankless water heaters can be amplifiers too, so no free pass on using them in open potable/hydronic systems. 

Chlorine at levels utilized in municipal water systems has no effect on Legionella bacteria and the amount of chlorine required to suppress Legionella population would be harmful to humans. In addition, chlorine does not penetrate biofilms well. Chlorine dioxide and copper/silver ionization do work well in suppressing the bacteria, but are not commonly used for our potable water systems. 

What can be done?

If we raise potable water temperatures above 133°, we begin to kill off Legionella bacteria. However, that requires contact time — typically 20-minutes or longer — and the little beasties can survive super-heated flushes (160° or hotter) by living within biofilms and sediment layers. 

Knowing these facts, we maintain our home’s potable hot water at 140° and have constant 24/7/365 circulation from our indirect water heater to the far end of the distribution piping and back to the tank’s drain valve tee. The return remains above 133° at the tank.

Scalding becomes a more pressing issue once you exceed the factory setting of 120°, so if you, or your customers, decide to set your domestic hot water for a target temperature of 140° (or higher), you’ll need to incorporate an ASSE-Listed thermostat mixing valve either at the water heater’s outlet or at points of use where human contact will occur. Given that codes already require ASSE compliant scald-guard tub/shower faucets, the remaining lavatory and kitchen faucets are easily protected. 

As for the hydronic side of open unprotected systems, the stagnation issue is supposedly overcome by utilizing a timer to “exercise” the circulator or else incoming potable water is run through the hydronic side to “freshen” the otherwise stagnant water. This can present other issues such as cold water condensation on concealed underfloor piping with the potential for growing mold! 

Best practice, from my perspective, and using common sense, is to protect your customers by keeping the potable and hydronic waters isolated from each other using a stainless steel flat plate heat exchanger. Although the national plumbing codes currently allow the installation of open potable/hydronic systems, knowing that such systems create a bacteria amplifier that suits Legionella reproduction to a T, renders that a no-go in my book from a liability standpoint. 

Cooling towers

Cooling towers also offer Legionella an ideal breeding ground, and testing has indicated 50% to 80% of cooling towers contain Legionella bacteria. 

In the fall of 2017, 22 cases of Legionnaire’s disease were traced to a cooling tower as the likely source at Disneyland. Disneyland denied being the source of the outbreak. However, two Disneyland cooling towers revealed high levels of the bacteria from tests conducted around the time of the outbreak. 

The cooling towers were disinfected and Disneyland was never fingered as the source, and according to a Los Angeles Times article, Disneyland spokeswoman Suzy Brown said, “We strongly object to Cal-OSHA’s allegation that our cooling towers caused any illness, since the source of the outbreak has never been scientifically determined.”  

Cal-OSHA utilized records by one of their safety engineers indicating Disneyland did not follow proper guidelines to disinfect its cooling towers, which allowed the bacteria to flourish. However, the Disneyland cooling towers were never definitively proven to be the source of the outbreak. 

The fact remains cooling towers can be a suspect for Legionnaire’s disease outbreaks. Imagine this on a much smaller scale at your local level if one of your client’s cooling towers you service were to be identified as the source for folks being sickened. I’ll detail those issues next month. 

This article is also available at: https://www.pmmag.com/articles/102970-dave-yates-legionella-in-hvac