In spite of the ubiquitous nature of the bacteria which lives in lakes and rivers around the world it wasn’t until an outbreak at an American Legion convention in Philadelphia, PA, USA in 1976 that the bacterium was first discovered. The disease, a mystery at first, was coined Legionnaires’ Disease and the culprit named Legionella. Since that time further studies and diagnoses have identified the Legionnaires bug as one of about twenty of a family of Legionella, Legionella pneumophila, the worst of the bunch in terms of human health and safety.

The 1976 outbreak was traced to the cooling system of the hotel where the legionnaires were holding their convention. The condensate pans beneath the cooling towers on the roof were poorly drained allowing pools of warm water to collect which is an ideal environment for the bug to proliferate. During the investigation by the Centers for Disease Control and Prevention (CDC) it was found that concentrations inside the hotel were surprisingly low compared to samples taken on the street due to wind conditions blowing water droplets out of the pans and effectively aerosolizing the streets below! Contaminated water droplets breathed into the lungs is the main cause of infection.

So how does this affect plumbers? It’s an HVAC issue isn’t it? It certainly is an HVAC issue, one that technicians, installers and engineers should be apprised to protect both their clients and themselves when working on these systems. But plumbers should take notice too, since it has come to light that water distribution systems are at risk of harbouring the villain, possibly more so than any other!

When you’re working on an existing system have you ever noticed the slime that forms on the inside of some water pipes? It’s a biofilm comprised of waterborne microbes, protozoa and other microorganisms attached to the sides of pipes, tanks and other components that make up the distribution system. It’s also an excellent place for legionella to thrive if the temperatures are between 40° – 50°C (104° - 122°F). Temperatures above or below this range tend to inhibit growth however temperatures sustained above 60°C (140°F) are required to kill it. Knowing this one might want to examine that domestic hot water system a little more closely.

And DHW systems are exactly where they’re finding the bug. Larger buildings seem to be more prone to contamination, possibly due to the sheer size and volume of these systems although that is mere speculation at this point and deserves further study. Certain studies either previously conducted or currently underway have found upwards of 70% of hospitals tested in England, Canada and the United States to have legionella contaminated water distribution systems in both the hot and cold water piping! This may sound incredibly alarming and in a few of those cases it certainly was, however the presence of L pneumophila won’t necessarily cause Legionnaires’ Disease unless in a sufficient quantity and/or the person in contact has a weakened immune system. But I don’t have to spell out the consequences if left to propagate.

Early tests had shown the bug to be in highest concentration within the scale and sludge found at the bottom of hot water storage vessels and it was deduced that this was the breeding ground and consequently the place to launch the attack. Health officials were recommending operating all water heaters at 60°C or higher since the high temperatures are very effective at killing legionella. However this will only kill bacteria within the heater itself and it was quickly becoming evident that the bacteria could be present elsewhere in the system and recolonization would be imminent.

Legionella can colonize on a variety of plumbing materials, including plastics and stainless steel. Copper is also prone but less so than other materials. Avoid natural rubber in gaskets and faucet washers, too, as the bug seems to do very well on these surfaces. Glass and other vitreous tank linings don’t deter the bug either, however the configuration of the tank does. Tests have revealed that, for some reason, horizontal tanks were significantly less prone to contamination than vertical tanks. It would be interesting to find out why that is. Other places to look are water hammer arrestors, dead-end piping, shower valves, showerheads and faucets.