Legionella Prevention

     This Rule of Thumb Thursday topic was derived directly from a google search. “As a general rule of thumb, you should remember the following: keep hot water hot, cold water cold, and keep the water moving,” but is this justified?

     Legionella was discovered about six months after the Pennsylvania Department of Health and Centers for Disease Control and Prevention (CDC) began investigating reports of illness among Legionnaires who had attended the annual convention of the American Legion's Pennsylvania Chapter at the Bellevue-Stratford Hotel in Philadelphia,  July of 1976. The outbreak of what became known as “Legionnaires’ disease” struck 221 persons, 72 of whom did not attend the convention but were in or near the Bellevue-Stratford Hotel over the same period. 34 died (Fraser 1976).

     Legionella is a genus of pathogenic gram-negative bacteria that can cause legionellosis (all illnesses caused by legionella). It is a type of bacteria that causes two forms of pneumonia – Legionnaires’ disease and Pontiac Fever. Both conditions develop when the bacteria are inhaled through water droplets or vapor. The disease is not communicable and does not occur if Legionella is ingested.

     According to the CDC, anywhere from 8,000 to 18,000 cases are reported in the U.S. each year. Because the disease is difficult to distinguish from community-acquired pneumonia and the onset of symptoms occurs several days after contact, many more incidences probably go unnoticed. The bacteria are most likely to affect those with weakened immune systems, including children, those with reduced lung capacity, the elderly, and people with auto-immune disorders. The CDC also estimates that 5-30% of Legionnaires’ victims perish. Many patients recover with the aid of antibiotics, but some require hospitalization for days. A growing number of reports also show that victims can have lasting neurological damage, largely affecting memory and muscle control. Along with other waterborne diseases such as giardiasis and cryptosporidiosis, Legionella costs the healthcare system up to $500 million annually, according to CDC research. By using insurance claims, it was calculated that Legionnaires’ disease places a $100-340 million burden on patients, insurers, and taxpayers. For example, a single hospitalization for Legionnaires’ averages more than $40,000.

Beyond obvious places like cooling towers and hot tubs, there are many areas in a building vulnerable to Legionella. These include drinking water systems, hot water tanks, showers, misters, ice machines, fire sprinklers, and water features such as decorative fountains and water walls. Even respiratory devices and humidifiers in healthcare settings have been called into question. The likelihood of Legionella does not necessarily depend on the type of water system in question, but rather the conditions within that water supply. Certain environments will promote Legionella to breed at dangerous levels more so than others. “Legionella will flourish under three conditions,” says Simon Turner, president of Healthy Buildings. “It needs an optimum growth temperature between 77-115 degrees F, the presence of biofilm to provide a source of nutrients and an accumulation of sediment or scale that will shield it from chlorination.”

     One major cause of Legionella growth can be attributed to dead legs in plumbing lines that are common in older buildings with a history of renovations. “Water becomes stagnant in these abandoned pipes and can’t be properly sanitized or flushed out, yet it will constantly seed the rest of the plumbing system with Legionella,” Turner explains. The water in these areas does not circulate, and warm, stagnant water creates a particularly conducive environment for many kinds of bacteria to proliferate. Biofilms are able to flourish under conditions of low flow. These dead leg sections also make it difficult for water treatment chemicals to adequately contact areas of stagnation and if not eradicated, can even make the situation worse as biofilms can detach and settle downstream.

     Alternatively, high flow rates and turbulence can proactively reduce the formation of biofilm. At lower residence time, the erosion of cells on the surface due to higher shear force and enhanced diffusion of disinfectant within a thinner boundary layer are factors suggested to explain the effect of flow dynamics on biofilm formation (Donlan et al., 1994).

     There are many guidelines that indicate control of Legionella can be obtained by keeping the hot water at/above 140°F in water heaters and above 120°F at distil outlets, and by keeping cold water lower than 70°F. Unfortunately, Legionella may multiply at temperatures outside of these thresholds where biofilms or other complexities exist. Current studies differ in the maximum temperature observed for pneumophila growth, where some researchers observed growth in excess of 115°F. Several factors can be attributed to their growth, such as the types and species of amoebae present. It remains a best practice to avoid water temperature between 77-115°F but will not guarantee eradication of related bacteria.

     As it is commonly accepted that water is a living organism, so true is it that all domestic water systems should be addressed specifically. The related rule of thumb presents a much larger attention requirement than that given in this short article. In any water management plan, one could argue that effectiveness can be correlated to the control measures presented, means of verification and consequent remedial actions. Although I would agree with the rule of thumb as a general maintenance strategy, there are a plethora of additional parameters that need to be addressed when considering the overall health and safety of a building’s water. Such parameters include excess nutrients, pipe corrosion, chemical disinfectants, residence time, serogroups present, ambient climate, and many more. Hopefully, these parameters can be further investigated in future “ Rule of Thumb Thursdays”.

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Legionella Prevention Wisconsin
Dead legs Wisconsin Legionella
Legionella Bacteria

Legionella bacterium (green) caught by amoeba (orange)

Jed Kosch

ASSE 12080 Certified - Legionella Water Safety & Management