Legionella, particularly Legionella pneumophila, is a bacterium that is known to proliferate in complex water systems, such as cooling towers, hot tubs and even domestic plumbing. Being exposed to this bacterium, usually by way of aerosolized water droplets, might result in serious illnesses like Legionnaires’ disease. Due to the potentially fatal consequences of Legionella infections, it is critical to demonstrate the efficacy of disinfectants through rigorous disinfectant testing against Legionella in these water systems.
Stringent testing standards like EN 13623 are employed to check the efficacy of disinfectants intended to be used to reduce the risks posed by Legionella. Here we explore the standard, test parameters, its requirements and the significance in ensuring the efficacy of disinfectants for Legionella control.
What is EN 13623?
The risks associated with Legionella are moderated by the use of effective disinfectants. Basically, this standard disinfectant testing against Legionella is applied to water systems such as cooling towers, spas, showers and swimming pools in which its multiplication is a high risk to human health.
The test method described in EN 13623 is a phase 2, step 1 test, which means that it has been designed to determine the basic bactericidal activity of a disinfectant in the laboratory before it is tested under field conditions.
Test Parameters and Requirements
The EN 13623 standard is highly specific regarding the parameters that need to be tested. Critical parameters include test organism, temperature, contact time, diluent, interfering substances, among others. Below is a brief discussion on the critical test parameters:
Test Organisms
This standard requires the test organism Legionella pneumophila subsp. pneumophila (ATCC 33152). Other strains, such as Legionella pneumophila serogroup 1 Benidorm (NCTC 12006, ATCC 43108), can also be used for specific applications. Disinfectant testing against Legionella involves culturing these organisms under specified conditions such as incubation at a temperature of 36 ± 2°C.
Temperature and Contact Time
Disinfectant efficacy is indeed assessed by testing under controlled conditions, which include specific temperatures. In cooling water systems, this is performed at a temperature of 30°C, while for general-purpose water systems, it is conducted at 20°C. The contact time is influenced by the speed of action of the disinfectant. Products that work quickly are tested for a contact time of 60 minutes, while for the slowly acting products this time can go up to 15 hours.
Interfering Substances
Interfering substances, such as yeast extract, are added to the culture medium to simulate actual conditions. The concentration used is 0.0005%. This ingredient provides for the organic material probably present in a water system and may act to neutralize the efficiency of disinfectant under field test conditions for Legionella disinfection.
Diluent
The selection of diluents for different types of water systems in disinfectant testing is determined by the specific requirements of the test. Hard water is used as the diluent for general purpose water systems. For cooling water systems, buffered ferrous hard water is used. The pH and hardness of the water should be controlled to simulate the conditions that the disinfectant would encounter in real applications.
Test Methods and Procedures
The EN 13623 standard describes a complete test method to ensure that the bactericidal activity of the disinfectant is accurately determined. This process includes the following steps:
Preparation of Test Organism Suspensions
A test suspension of Legionella pneumophila is prepared using a validated method. The suspension is mixed with the disinfectant diluted in hard water or buffered ferrous hard water. Certain temperatures and contact times need to be maintained for effective disinfectant testing against Legionella.
Neutralization of Disinfectant Activity
Following contact time, an aliquot of the mixture is withdrawn and the bactericidal activity is neutralized. The reason being that the disinfectant might otherwise exert its activity on the bacteria beyond the contact time of the study. The method of choice to arrest the bactericidal activity of the disinfectant is dilution-neutralization. However, if this is not suitable, then membrane filtration may be used.
Calculation of Bactericidal Activity
This defines the number of living bacteria in the sample and evaluates the log reduction in bacterial count. This reduction should be achieved under the required test conditions such as a temperature of 20°C for general-purpose water or at a temperature of 30°C for cooling water, using the contact time as prescribed. A disinfectant should exhibit at least a four-logarithmic reduction corresponding to 10,000-fold reductions in bacterial count in order to be considered effective for bacterial control.
Interpretation of Results
Test results are expressed in terms of log reduction. If the log reduction required by the standard is obtained with the disinfectant, it will be considered bactericidal against Legionella pneumophila under the specified test conditions. It should be noted that EN 13623 disinfectant testing against Legionella is targeted at shock treatment disinfectants applied in a single dose to kill Legionella. The test cannot be used to assess disinfectants dosed into the water system as part of a continuous regime to control bacterial growth over a period of time. Further, biofilm formation, particular water chemistry and specific pH range may all impact the actual efficacy of the disinfectant.
The Role of EN 13623 in Public Health
EN 13623 assumes great importance in the safeguarding of public health by ensuring that chemical disinfectants developed for action against Legionella in water systems are effective. Compliance enables a manufacturer to validate his product for bactericidal efficacy, providing confidence to users in a wide range of industries such as healthcare, hospitality and water treatment.
Disinfectants that pass the EN 13623 disinfectant testing against Legionella can be marketed as effective against Legionella, reducing the risk of Legionnaires’ disease outbreaks in high-risk environments like hotels, hospitals and industrial cooling towers.
EN 13623 provides a robust framework for evaluating the efficacy of disinfectants against Legionella in water systems. The standard specifies precise test conditions and methodologies to ensure that disinfectants are capable of achieving significant reductions in bacterial count, thereby safeguarding public health. Whether in cooling towers, spas or domestic water systems, ensuring the efficacy of disinfectants is essential in controlling the spread of Legionella.
Disinfectant testing against Legionella at MIS
Microbe Investigations Switzerland (MIS) offers expert Testing and Validation Services as per EN 13623 standards. Our laboratory provides comprehensive services for testing disinfectant efficacy against Legionella. Contact us today to learn how we can help you achieve your Legionella control goals.
