Legionella testing required for medical water systems
The presence of microbiological organisms in water can be complex to interpret. There are bacteria that are good for us, like the ones that live in our digestive system and help us digest food, and there are bacteria that are dangerous and can make us sick if ingested or inhaled. Additionally, there are opportunistic bacteria that can cause illness if the right circumstances exist, such as if a person has a weakened immune system.
Under the Safe Drinking Water Act, public water supplies are required to test for coliform and E. coli bacteria. These bacteria are found in the same places as more harmful bacteria, so their presence could indicate the presence of other, more infectious disease-causing bacteria.
Legionella is regulated under the Safe Drinking Water Act as a treatment technique for surface water systems, which means that surface water systems must follow certain treatment techniques that should remove Legionella along with other dangerous microorganisms, such as Cryptosporidium and Giardia. This means Legionella is not a required test for public water supplies unless there is an incident that prompts the system to perform additional testing. Additionally, Legionella happens to be non-coliform bacteria, so the required tests done by public water supplies will not indicate a presence of Legionella. Knowing whether there is a Legionella risk requires other testing methods.
Legionella is an opportunistic pathogenic bacteria known to cause Pontiac fever or the more serious Legionnaires’ disease. Legionella is found in many aquatic environments, but it thrives in hot tubs, decorative water fountains, hot water tanks, heaters and cooling towers. While the bacteria can cause disease, it must be inhaled via fine water droplets from cooling towers or from showering. It also can be inhaled by aspirating drinking water. Consequently, simply ingesting water containing Legionella does not cause illness. The majority of healthy individuals who are exposed to Legionella do not get sick. However, certain individuals are at a higher risk of infection, including people over the age of 50, those who smoke or have smoked, and anyone with chronic lung disease or a weakened immune system.
On June 2, 2017, the Center for Medicare and Medicaid Services introduced a requirement for hospitals, nursing homes and other facilities providing medical services to implement water management plans to reduce the risk of Legionella outbreaks. The requirements are based on standards developed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) for developing and applying water management plans and risk control in large or complex building water systems. Part of developing a plan is testing its effectiveness, so testing is highly recommended. When testing for Legionella or an indicator organism, a variety of methods exist, and each has advantages and disadvantages.
Let’s first consider testing for indicators of Legionella. A great indicator test commonly used is heterotrophic plate count (HPC), also referred to as called standard plate count. This test looks for non-coliform bacteria which includes Legionella as well as several other opportunistic bacterium. While high HPC levels may not be dangerous to most people, they do represent a significant risk to anyone who has a compromised immune system. This test commonly is used to determine the effectiveness of disinfection. HPC levels are not regulated under the Safe Drinking Water Act, so there is no maximum contaminant level, but there is a guidance level of 500 cfu per mL. When levels are above 500 cfu per mL, additional testing may be recommended to ensure safety.
Tests for HPC should be done at a certified laboratory. When collecting these samples, remember that this test has a very short holding time and needs to be received by a lab within 6 to 24 hours, depending on the state’s certification program. Samples will need to be put on ice, and if shipped must be at 10°C or less when received, while samples transported to the lab must show evidence of samples being cooled, such as the presence of ice and a cooler.
Another indicator test is a slime-forming bacteria test, which provides an optimum environment for Legionella. There is a biological action reactivity time test for slime-forming bacteria that can be performed in-house or at a laboratory. This indicates estimated counts of bacteria colonies based on the reaction time. The more bacteria present, the quicker the analysis will be completed. It can take several days to confirm a negative result. While not necessarily an indicator test, it is important to monitor disinfectant levels and temperatures, as they can significantly impact bacteria levels. Temperature and disinfectant levels are easily tested on site, so they should be done on a daily basis or more as required by the water management plan.
Testing Types & Tips
In the U.S., Legionella testing is primarily certified by the Centers for Disease Control and Prevention (CDC), although some states have implemented Legionella certification in recent years. The CDC has a program called Environmental Legionella Isolation Technique Evaluation, or ELITE for short, which helps a laboratory by creating ways to test its technique against standardized samples to evaluate its isolation technique.
The main method used for running Legionella is a culture method. Currently this is the only method approved by certifying agencies, but there is a movement to accept some newer methods. The culture method looks for most species and 12 serotypes of L. pneumophila, which is the pathogenic species that causes Legionnaires’ disease. This method takes 10 days to confirm a negative result, so testing can take some time. This analysis is quantitative and will give an estimated count of bacteria present. The sample size depends on what is sampled. Usually a 1,000-mL sample is required for potable water and a 250-mL sample is required for non-potable water.
Samples should be preserved with sodium thiosulfate and be cooled before being the laboratory receives them. They should arrive at the laboratory within 24 hours of collection, so be sure to collect the sample at the proper time. Take into consideration time zone changes if shipping samples, to ensure the lab has enough time to receive and prepare for analysis. The lab should provide its sampling instructions so the samples arrive in the proper condition.
While the culture method is the standard for testing, newer methods that provide quicker results are emerging. When it comes to an outbreak, quicker results can be helpful. One such method is commonly referred to as the polymerase chain reaction and can provide results within 24 hours.
However, there are some drawbacks. This method only provides a present or absent result, and it does not distinguish between active and non-active organisms. There also can be false negatives, depending on the sample matrix.
This method works by measuring DNA or RNA material, and it is an excellent screening test when trying to identify the source of Legionella. The results of this analysis should be confirmed using the culture method.
Legionella is a serious microbiological contaminant. in 2015, there were approximately 6,000 cases of Legionnaires’ disease reported, and the CDC thinks that is an underestimate because it often is misdiagnosed. Legionnaires’ disease can be deadly, as nearly 1 of 10 people who develop the disease are likely to die from it.
Hospitals estimate the cost of treating Legionnaires’ disease to be about $450 million annually, so it is expensive and taxes our health care system. This is a preventable disease, and with the increase in incidence over the last few years, regulations aimed at reducing these risks are timely. The new regulations address buildings that house at-risk individuals and do not use a cookie-cutter approach. Each building must be evaluated based on various factors and require testing be conducted to ensure systems serving at-risk individuals are safe.