CMS SOM App. H, Tag V219

7 Strategies for bacterial control

7.1 General (disinfection and frequency)

Routine low-level disinfection of the pipes should be performed to control bacterial

contamination of the distribution system. The frequency of disinfection will vary with the

design of the system and the extent to which biofilm has already formed in existing systems,

but disinfection must be performed at least monthly.

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A mechanism should be incorporated in the distribution system to ensure that disinfectant

does not drain from pipes during the disinfection period.

Interpretive Guidance § 494.40(a)

ANSI/AAMI RD52:2004

7 Strategies for bacterial control

7.1 General

The strategy for controlling the proliferation of microorganisms in hemodialysis systems

primarily involves proper system design and operation, and regular disinfection of water

treatment system and hemodialysis machines. A key concept in ensuring compliance with water

bacteriology standards is that disinfection schedules should be designed to prevent bacterial

proliferation, rather than being designed to eliminate bacteria once they have proliferated to an

unacceptable level (i.e., above the action level). With this strategy, monitoring levels of bacteria

and endotoxins serves to demonstrate that the disinfection program is effective, not to indicate

when disinfection should be performed. Gram-negative water bacteria, their associated

lipopolysaccharides (bacterial endotoxins), and nontuberculous mycobacteria (NTM) most

frequently come from the community water supply, and levels of those bacteria can be amplified

depending on the water treatment system, dialysate distribution system, type of dialysis machine,

and method of disinfection.

Two components of hemodialysis water distribution systems—pipes and storage tanks—can

serve as reservoirs of microbial contamination. Hemodialysis systems frequently use pipes that

are of larger diameter and longer than are needed to handle the required flow. Oversized piping

slows the fluid velocity and increases both the total fluid volume and the wetted surface area of

the system. Gram-negative bacteria in fluids remaining in pipes overnight multiply rapidly and

colonize the wet surfaces, thus producing bacterial populations and endotoxin quantities in

proportion to the volume and surface area. Such colonization results in the formation of

protective biofilm that is difficult to remove once formed and that provides a barrier between the

bacteria and germicide during disinfection.

Biofilms are communities of microorganisms attached to surfaces. They form just about

anywhere a nonsterile fluid flows over the surface. Biofilm increases the ability of

microorganisms to compete for nutrients and other resources. The complexity of biofilm depends

on the degree of water or fluid movement and the availability of nutrients. Thicker biofilm, and

usually a greater diversity of microorganisms, will form in slower-moving waters; in faster-moving waters, it is harder for microorganisms to become (and remain) attached to the surface,

so biofilm formation takes longer. Organisms living within biofilm are shielded by an

extracellular polymer or glycocalyx. This glycocalyx provides the bacteria with some protection

from the action of disinfectants. Biofilm may exist throughout a hemodialysis distribution system.

Once established in a distribution system or dialysis machine, biofilm can be difficult to

eradicate. Bleach and ozone are generally the most effective agents for biofilm removal, and

their use may be more efficacious if the pipes are treated first with a descaling agent. However,

in some cases, complete or partial replacement of the distribution system may be the only way to

eliminate biofilm.

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Additional Guidance:

In order to minimize the risk of development of biofilm, every dialysis facility must disinfect their

water distribution system at least monthly.

Delineation of what constitutes sufficient contact time of an EPA-registered disinfectant is

typically determined by the manufacturer. All surfaces in the water distribution system must have

sufficient contact, as instructed by the manufacturer, time with the disinfectant prior to its being

rinsed from the system.