Cover Story
The Latest on Legionella
by Matthew R. Freije
March 1, 2010
Draining water from infrequently used hospital dialysis hookup lines is one example of how to combat the formation of Legionella bacteria. Photos courtesy Matt Freije
Plumbing engineers can minimize this prevalent hazard through education and preventive measures.
Most of us have
made the mistake of ignoring a problem, hoping it will just go away, instead of
doing what we can to improve the circumstances. And then, once we devise a plan
and get to work, we find the problem is more manageable than we
realized.
Legionella is a problem that will not vanish without intervention but can be
greatly minimized with proper design, construction, operation and maintenance
of plumbing systems. Because plumbing engineers play a key role in prevention,
they must stay up to date to protect health and life and to reduce their legal
risk.
Here is the latest on Legionella and a forecast of what is likely to come.
Prevalence
Because more than 90 percent of Legionnaires’ disease cases
are not even detected, let alone reported to health authorities or by the
media, many people perceive the disease as rare, but it is actually quite
prevalent and possibly on the rise. The number of reported cases rose 70 percent
from 2002 to 2003, with the largest increase in the Eastern states, according
to a report in 2008 by Neil Berkelman. Of the reported cases occurring from
2000 to 2005, 63 percent were in people less than 65 years old.
Litigation
Studies have sown electronic faucets to be more conducive to Pseudomonas and Legionella than manual faucets.
In addition to building owners, defendants have included general contractors, plumbing contractors, water-treatment companies, engineers, architects, manufacturers and water utilities.
As the number of diagnosed Legionnaires’ cases increases because of physician awareness and better and cheaper clinical tests, the number of lawsuits is likely to increase as well. Plumbing engineers should check their professional liability (errors and omissions) insurance policies to ensure coverage for claims related to bacteria are not excluded.
Regulations and Guidelines
An electronic mixing valve to better control temperature in a hot-water loop may be a good idea, but must be thoroughly evaluated.
This year and next, the document likely to affect plumbing engineers the most is the new ASHRAE Legionella standard, expected to be released for public review late this year. The current ASHRAE Legionella document, issued in 2000, is a guideline whereas the new one will be a standard, which has more muscle.
The ASHRAE standard is likely to advocate a proactive approach to the prevention of Legionnaires’ disease, emphasizing the need for a water-management plan similar to what is recommended by the World Health Organization. Although ASHRAE will not likely give a specific recommendation for water testing, the standard may require an owner to validate preventive measures, which can best be done by testing water for Legionella.
The ASHRAE standard will likely increase demand for Legionella assessments and management plans. Type here
Water Testing Technology
The culture method is still considered the standard but as newer technologies are refined, validated and accepted by the scientific community, Legionella water test results will be available in one or two days (instead of seven) after a sample is collected, more accurately quantified, and more specific in the species and serogroups reported. It won’t happen this year but quite likely will happen before the decade is half over. If the new testing technologies are also lower in cost, Legionella sampling will be more widely used.
Green Building Initiatives
Copper-silver ionization is still a method primarily used in domestic water remediation.
Hospitals are not the only buildings facing choices between waste and stagnation. Hotels, for example, can minimize Legionella bacteria by running the water in vacant rooms.
Complexity in Plumbing Systems
Extra piping, fixtures and valves add surface area and
crevices where biofilm can develop and stagnation can occur. Thus, heat
recovery systems, mixing valves, extra faucets to encourage hand washing and
other complexities may ultimately do more harm than good.
For systems with a storage tank that holds a day or more of hot water, a master
thermostatic mixing valve may help to minimize Legionella by storing water at
140°F or higher and then mixing it down to a safer temperature for delivery to
fixtures.
But if smaller water heaters are used (such as semi-instantaneous heat
exchangers that hold only about 20 gallons), heating the water to 140°F and
then mixing to a lower temperature will do little or nothing to control
Legionella because the water will not be at 140°F for enough time to kill the
bacteria (Legionella die in about 32 minutes at 140°F). The mixing valves in
such a scenario could actually increase the risk of Legionella by adding
surface area to the system.
Electronic faucets are another example. Studies have shown them to be
significantly more conducive to Pseudomonas and Legionella than manual faucets.
Legionella was found, not only in the water flowing out of the electronic
faucets, but in the biofilm on the inner components.
Technologies for maintaining temperatures and flow in various parts of plumbing
systems, including right at shower fixtures, have recently been introduced in
Europe but testing must be conducted to determine whether the designs actually
minimize Legionella and other biofilm-associated bacteria.
Complexity, however, is not always a bad thing. An electronic mixing valve to
better control temperature in a hot-water loop and solenoid valves to bleed
water at stagnant points in a system may be a good idea, but each design needs
to be thoroughly evaluated. Everything else being the same, engineers should
prefer the simple to the complex.
Water Testing for New Construction
A chlorine dioxide generator
The AWWA C651 recommendation to hold a chlorine concentration of 50 parts per million in the entire system for 24 hours, or 200 ppm chlorine for three hours, is appropriate for most buildings and agrees with the ASPE’s handbook. But some of the options described for post-chlorination validation testing are either vague or totally inappropriate for building plumbing systems.
For example, the document states samples will be collected from every 1,200 feet of the new water main, at the end of the line and from each branch. If this guideline was to be applied to a building plumbing system, as was recently proposed by the designer of a new hospital, a ridiculous number of costly samples would be required. Also, an HPC (heterotrophic plate count) test, which the AWWA states is optional, is not an appropriate post-chlorination validation test.
HPC is a poor indicator of health risk. In fact, studies of cooling towers and home plumbing systems have shown HPC bacteria may actually protect against pathogenic (disease causing) organisms.
In April 2002, beginning one day after the International Symposium on HPC Bacteria, the World Health Organization held a meeting in Geneva, Switzerland, on the scientific basis for interpretations of HPC measurements. The experts arrived at a consensus that HPC bacteria in drinking water was not associated with a significant health risk. The U.S. EPA subsequently removed the requirement for HPC levels below 500 cfu/ml in public water supplies.
Additionally, the AWWA states the system will show the absence of coliform organisms. Although coliforms are certainly not perfect indicator organisms, testing for them is appropriate since a coliform test is standard for U.S. drinking water.
Some engineers have written specifications requiring “no live bacteria” following the chlorination procedure, but that is not feasible or reasonable in a plumbing system. First, “no live bacteria” is vague because it does not state which type of test should be used or the number of points in the system to sample. Second, to require a plumbing system to have zero live bacteria would put it on the level of a high-purity pharmaceutical or electronics manufacturing system.
A proper specification for plumbing disinfection is important. If the requirements are lax, the people who occupy the building may get sick. If the requirements are excessive, it will unnecessarily add to the project cost and possibly delay the opening of the building. here
Domestic Water Remediation
A point-of-use submicron filter may be needed on some fixtures that remain Legionella-positive.
With the aging population and increasing threat of waterborne organisms resistant to antibiotics, plumbing engineers will continue to play a key role in minimizing disease.
Matthew R. Freije
mf@hcinfo.com
Matt Freije is president of HC Information Resources Inc., Fallbrook, CA (www.hcinfo.com). He is the author of the book Legionellae Control in Health Care Facilities: A Guide for Minimizing Risk and three new Legionella management plans for hospitals, hotels and nursing homes. He is also the editor of Legionella Enews, an international newsletter that covers outbreaks and new technology. Freije conducts Legionella building assessments, serves as an expert in litigation related to Legionnaires’ disease, recommends domestic water disinfection strategies and teaches seminars. He can be reached at (760) 451-1050, or mf@hcinfo.com.
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