Testing Mechanical Water Filtration Systems for Microbial Reduction in Healthcare Settings
By Rick Andrew
Healthcare facilities have increased focus on infection prevention in recent years. Many of their patients are immunocompromised and therefore more susceptible to infection, so this increased focus can have a significant impact on public-health outcomes. One of the major sources of infection is waterborne pathogens such as Legionella pneumophila, Mycobacterium avium and Pseudomonas aeruginosa. With waterborne pathogens playing a significant role in healthcare-acquired infections, there has been increasing awareness and action taken to help assure the safety of water systems within healthcare facilities.
In fact, in 2017, the Centers for Medicare & Medicaid Services implemented a requirement for healthcare facilities to conduct a facility-wide water safety-risk assessment, implement a water management plan and define and specify testing protocols, acceptable ranges for control measures and document specific actions that will be taken when control limits are not met.(1)
Water filtration technologies play a key role in these efforts. They are widely used in healthcare settings, especially POU technologies for showers and handwashing in sensitive areas such as burn units. Recognizing the need for a tool to help healthcare facilities have confidence in the safety and performance of these products, NSF has developed a new protocol, P376 Mechanical Water Filtration Systems for Microbial Reduction in Health Care Settings.
Scope of the protocol
Published on August 9, P376 addresses POU mechanical water filtration systems designed to retain bacteria and fungi that may be present in water supplies in healthcare settings, including, but not limited to, hospitals and dental clinics. Systems covered under the protocol are intended to reduce bacteria and fungi that may adversely affect the health of patients, especially those who are immunocompromised. The protocol establishes requirements for POU drinking-water treatment systems and the materials and components used in these systems. Only complete systems are evaluated under the protocol, not components of systems. The protocol covers only mechanical filtration systems and is not intended to evaluate systems that include disinfectant agents.
P376 refers to NSF/ANSI 53 for evaluation of safety of materials in contact with water and also for structural integrity, although with a modification to test structural integrity at elevated temperature (46 °C) because of the potential for these systems to be used for filtering shower water. In terms of microbiological filtration, the protocol requires evaluation of three filter systems, all challenged with four different organisms (see Figure 1). The challenge organisms may be combined into one challenge suspension or they may be used separately during testing.
The testing is conducted at the maximum flowrate attainable at 60 ± 3 psig. The test period must cover 100 percent of the manufacturer-estimated service cycle, although the test is stopped and completed if the test units clog to a degree that the initial flowrate is reduced by more than 75 percent, or the manufacturer’s replacement flowrate, whichever is lower. The total test period must be at least three weeks to constitute a valid test. Because of these test-period requirements, the manufacturer must provide the testing laboratory with specific details regarding the service cycle for the product, in terms of the number of weeks systems are used prior to replacement, or indicating a reduced flowrate at which point it is assumed that users will replace the units.
For shower-head filtration system testing, the operation cycle is 15 minutes of flow, two times per day, with the two periods of flow at least eight hours apart. For faucet-filtration system testing, the operation cycle is one minute of flow per hour for 16 hours, with the other 59 minutes of each hour having no flow through the systems. Systems are operated five days per week, with weekend stagnation periods that have no flow through the systems.
Microbial challenging and sampling is conducted in accordance with Figure 2. In addition to the microbial challenges described in Figure 2, additional effluent samples are collected as the first water out of each test unit upon resumption of operation at the end of three of the stagnation periods. The first post-stagnation sample collection must be between 25 and 50 percent, the second collection must be as close as possible to the 65-percent service cycle point and the final collection must be as close as possible to 90 percent and preferably between 90 and 100 percent. Microbial challenge test-water characteristics are described in Figure 3.
A valid test must have a minimum of four microbial challenges and a minimum of two post-stagnation samples prior to stopping the test due to filter clogging. For this reason, it is acceptable to deviate from the challenge schedule and conduct more frequent microbial challenges if it appears that the test units will not reach 100 percent of the manufacturer’s claimed service cycle prior to reaching 75-percent reduction in flow (or the manufacturer’s end flowrate, whichever is lower).
To qualify as a POU mechanical water-filtration system for use in a healthcare setting, three production units of a type must continuously meet or exceed the reduction requirements in Figure 1, with allowance for measurement variability of not more than 10 percent of the influent/effluent sample pairs having less than the required log reduction by less than one order of magnitude. The percent reduction for each post-stagnation sample point is calculated using the geometric mean of the three previous influent concentrations and is evaluated against the criteria in Figure 1.
Like the NSF/ANSI Drinking Water Treatment Unit (DWTU) standards, NSF P376 provides a highly sophisticated, scientifically based, rigorous tool for benchmarking quality and establishing confidence in these products developed for a specific and sensitive end use, providing water for immunocompromised individuals in healthcare settings who may be susceptible to healthcare-acquired infections. End users can be assured that mechanical water-filtration systems evaluated in accordance with NSF P376 have cleared a very high bar to demonstrate that they will perform as expected and as needed to achieve their purpose.
About the author
Rick Andrew is NSF’s Director of Global Business Development–Water Systems. Previously, he served as General Manager of NSF’s Drinking Water Treatment Units (POU/POE), ERS (Protocols) and Biosafety Cabinetry Programs. Andrew has a Bachelor’s Degree in chemistry and an MBA from the University of Michigan. He can be reached at (800) NSF-MARK or email: Andrew@nsf.org