Legionellosis Linked to Limescale Buildup

Legionellosis is making the headlines again, with at least 15 confirmed cases in April in Auckland, New Zealand. The cases are spread throughout the Auckland area, making it difficult to find the source and supporting the idea it’s likely present in more than one source. One person in Auckland has died after contracting the disease.

Officials in the Auckland region have encouraged over 300 building owners to chemically treat or “shock-dose” their cooling towers with a biocide to kill the outbreak.

Legionellosis, or legionnaires’ disease, is a type of lung infection caused by a bacteria called legionella, according to the Centers for Disease Control and Prevention (CDC). Legionella bacteria thrive in wet conditions, but they must be inhaled or aspirated to cause an infection. The elderly or those with compromised immune systems are more at risk for contracting Legionnaires’ disease. Early symptoms, which begin two to 10 days after exposure, include headaches, fatigue, muscle aches and abdominal pain. Complications from the disease may include respiratory issues and kidney failure.

The CDC estimates between 8,000 and 18,000 cases of Legionellosis occur in the US every year, with more than 10% of the cases becoming fatal. The vast majority of cases of legionellosis are the result of exposure to legionella through a water system. The Building and Engineering Services Association claims the figure is potentially higher than the number purported by the CDC as the symptoms are often similar to the flu.

Any place moisture can build up may cause bacteria, such as legionella, to grow. The bacteria can grow in hot tubs, air conditioning systems (especially large commercial units), hot water tanks, plumbing systems and cooling towers. Limescale deposits in the water system allow water to pool when the fixtures aren’t in use. This pooling allows bacteria to grow and potentially infect those using or exposed to the system.

“By far the greatest risk lies within the humble hot and cold water systems, which deliver the disease through taps and shower heads. Legionella bacteria thrive in temperatures between 20-45 degrees Celsius; and if water is allowed to sit at these temperatures the bacterium can multiply into large numbers which can cause Legionnaires’ disease,” according to Simon French, a legionella expert and HVCA Service and Facilities Group member.

People involved in building management must understand the health risks associated with poorly maintained water systems. The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) publishes standard practices aimed at reducing the risk of legionellosis.

ASHRAE identifies the conditions in a building’s water system that make it less likely for legionella to grow and spread and recommends maintenance procedures and hazard controls to stop the spread of the bacteria. The standards are aimed at building/facility owners and managers, but they’re also useful to people involved in designing water systems to ensure their practices are adequate to prevent legionella exposure.

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  • Tim

    It may be semantics but moist environments support mold growth. Legionella must be in water as soon as the water dries the Legionella dies. It is a common misconception that large air handling units are a common source of Legionella outbreaks, they are at best a very very uncommon source of Legionella outbreaks. Most as many as 80% of outbreaks are from potable water systems. Cooling towers, spas and ornamental fountains are the other biggies. Humidifiers using tap water are a known source as well. Limescale may be an issue but it is not a significant one either. Standing water in dead legs, goose necks, shower hoses, drop legs for faucets / showers seldom used and even regular faucets is more of an issue. I’ve published several articles on misperceptions associated with Legionella. Misperceptions on the issue are all too common.

    May 15, 2012

    Presuming that “large air handling units” implies Cooling Towers, then while I agree, to an extent, with “It is a common misconception that large air handling units are a common source of Legionella outbreaks,” too much emphasis on this issue will lead to inaction on the part of maintenance staff. The Cooling Tower needs water, which water arrives via the potable water system, the inoculating culprit, but not the only one. It is imperative, if this health issue is to be addressed, that building owners and operator’s work with an experienced and competent consultant to focus on the risk areas and address preventive measures. As I stated in “LEGIONNAIRES DISEASE, PREVENTION & CONTROL, BNP 1983”, and in many articles, prevention is the key.

    The belief that “as soon as the water dries the Legionella dies.” may prove to be erroneous. Legionella, on entering protozoans, will multiply intracellularly to form cysts that are very resistant to drying and harsh chemicals, nature finds a way. Thus I leave you with, assume nothing, prepare for everything or suffer the consequences.
    F. Rosa

    May 16, 2012
  • Shame Onyou

    Although most cases are found in Cooling Towers or Large Air handling Units a lot of known cases in the UK are linked to hot and cold water systems. Mainly because they have been engineered in an incorrect manner for example some companies I have visited have a maximum of 15 outlets but would have a 15000L water tank to support them. You are only supposed to hold enough water in the storage tanks to last 24 hours. What i’m saying is a lot of Legionella cases come down due to lack of knowledge on the case, water heaters should be set at >50c as Legionella can thrive between 20-40c. Showerheads should also be disinfected and descaled on a 3 monthly basis in order to prevent a build up of scale that could be a homing ground for legionella.

    January 19, 2016
  • Michael Reed

    How about when a ball valves are used in hot water circulating ring mains and it is below 45 degrees, there is a small quantity of water trapped behind the ball in the open position, if there is lime scale present then wouldn’t this be a great environment for legionella to grow and when the ball valve was closed it would release the contaminated water into the circulating water.

    June 16, 2019

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