Tuesday, October 15, 2013

Developing a Prevention Plan for Legionnaires’ Disease

As temperatures continue to drop, it is important to remember that most cases of Legionnaires’ disease, which infects an estimated 8,000 to 18,000 people every year, are reported in the summer and fall, says Dr. Joseph Allen, senior scientist with Environmental, Health and Engineering (EH&E). Because this disease is transmitted from inhaling aerosolized droplets of water contaminated with the bacteria Legionella, proper maintenance of water systems is crucial, according to the CDC. However, as Allen explains, an effective prevention plan involves the proper assessment of many factors, and begins with understanding the basics risk factors and pathways of exposure. 

“One of the key messages we like to tell clients is that it’s a mistake to consider any one factor alone. [Legionnaire's disease] is multifactorial so you need to have a multidisciplinary team, to understand the building system, the epidemiology, the microbiology,” Allen says. “All of these factors play into understanding how this bacteria thrives and potentially causes exposure.”

Understanding common conditions that promote the growth of Legionella, hot spots in a building plumbing system and site-specific risk factors such as building size, population, water treatments and water use will foster a deeper understanding of basic risk factors and pathways of exposure. It is important to consider all  factors before developing a prevention plan against Legionnaires’ disease, he says.

According to OSHA, common conditions that foster the growth for Legionella include warm (68-122 °F) environments, stagnate water, a pH ranging between 5.0 and 8.5 and/or the presence of other micro-organisms. These conditions can be found in a multitude of areas within a building plumbing systems including: cooling towers, domestic hot-water systems, humidifiers, decorative fountains, showers, water faucets, spas/whirlpools, dental water lines, stagnate water in fire sprinklers, and in some cases, ice machines or any cold water source near enough to a heat source, Allen says.

Legionnaires' disease is frequently characterized as an "opportunistic" disease, often preying on individuals with underlying illnesses or weakened immune systems. According to OSHA, buildings, such as hospitals, with occupants with weakened immune systems, individuals 65 or older, smokers or people with chronic lung diseases need to be particularly cautious, as these groups are more vulnerable to the disease  The pathways of exposure are important to note as well, particularly in settings likely to house at-risk individuals. Showers, fountains and humidifiers all present means of aerosolizing the water, creating risk for exposure should the water be contaminated. 

Chemical water treatments are often used to combat the growth and spread of Legionella, and are generally effective, as long as the system is working properly. Factors that will affect the efficiency of a chemical treatment will include the pH level of the water and whether or not the system has any dead legs or stagnate zones, Allen says.  The effectiveness of chemical water treatments will vary depending on the pH level of the water, he explains, if only the pH levels of the treatment do not adequately offset the pH level of the water, the treatment may not be effective. Likewise, even if you have an effective concentration of the treatment, if it’s not reaching everywhere in the building’s plumbing system there will be areas left untreated. This was the case in a 2011-2012 outbreak of Legionnaires’ disease in the VA Pittsburgh Healthcare System that left five dead and more than one dozen sick. 

Keys to Prevention
Allen emphasizes that the key to a successful prevention plan is relying not on one method or denominator, but to consider a multidisciplinary approach. Each system is unique, so where to test and how often to test will vary based on an assessment of the building. He offers these tips for developing a plan to fit your facility:
  • Frequent testing of water samples, environmental samples and culture for the bacteria:
    • Look for prevalence/positivity of bacteria;
    • Look at concentration of bacteria;
    • Note the species of bacteria and the number of affected sites. 
  • Initial and periodic checking of the system for stagnate zones and/or dead legs.
    • Remember that building dynamics change over time, so it is important to monitor the system periodically to ensure it is working properly.
  • Improve system performance by removing dead legs or flushing distal outlets to
    ensure water circulation.
  • Ensure the water treatment is done at an appropriate level and that the cofactors and the pH is appropriate.
  • Avoid any “bright line” determiners, including the traditional 30 percent positive culture rate.
  • Increase surveillance (especially in hospitals):
    • Look for signs of outbreaks using urine antigen tests or cell culture from people who present with pneumonia.
Learn more about Legionella prevention at www.eheinc.com.