Waterborne Pathogens in Healthcare: Critical to Quality

WATER IS THE ESSENCE OF LIFE ON EARTH. When we hear the word water, we naturally and instantaneously draw an association with purity, cleanliness, and rejuvenation. Refreshment on a sweltering summer day, a hot shower on a frigid winter morning, and the ritual use of water in cultural and religious ceremonies are just some of the images that leap to mind in response to the mention of the word.

We rarely think of water as potentially harmful, but in reality, especially in the healthcare setting, water can be the carrier of morbidity and mortality. It constitutes a reservoir of risk to vulnerable patients, as well as a potential danger to healthcare workers, support staff, and visitors.

How can this be so? How can water be the bearer of disease and death in settings designed to restore health and vitality? In order to answer these questions, we must first understand that water is the natural habitat of many potentially pathogenic bacteria, fungi, and parasites.1-4 Secondly, we must become knowledgeable about the ability of these pathogens to form biofilm as they are transported by water to the point-of-use in modern plumbing systems. Finally, we must recognize that patients with weakened immune systems are exquisitely vulnerable to direct contact with pathogens in contaminated water, and that direct contact can take the form of a liquid stream, an aerosol, the ice in a beverage, or an improperly reprocessed medical device.

The water that is used in hospitals comes from the municipal water supply, a local well, or both.2 As it enters the hospital, water is diverted to hot and cold water supply systems. Cold water supply systems do not usually receive any additional decontamination treatment over and above that provided at the source, since its temperature generally discourages the proliferation of any waterborne microbes that might be present. Hot water, on the other hand, presents entirely different challenges.

In order for hot water to be available immediately upon demand and at the proper temperature, it is necessary in multi-level hospital buildings to construct a hot water recirculation loop. Hot water in this loop is continually flowing so that it can be periodically returned to the system boiler for reheating. The sustained elevated temperature of the hot water loop creates an opportunistic environment for waterborne microbes to multiply and form biofilm on the internal surfaces of plumbing system pipes and fixtures.

Hot water systems are generally subjected to various systemic disinfection modalities and protocols. However, systemic sanitization programs are rarely used without prior evidence of a problem in hospitals and, if they are used, they are not always effective.5-7 Municipal disinfection is often assumed to be adequate unless a specific problem has been identified. Upon recognition of problems, however, a variety of treatments are available, including hot water flushing,8 chlorination,9 electro-chlorination,10 chlorine dioxide,11 ozone,12 or copper and silver ionization.13-14 A recent in-vitro study compared many of these showing they were not comparably effective.15 The problem with many of these treatments is that they fail to uniformly and consistently deliver the designated minimal effective concentration of the disinfection agent to all points in the plumbing system. This is largely due to the protective effects of biofilm and Acanthamoeba, a protozoan commonly found in water that can harbor pathogens and protect them from many disinfection agents.16 Hartmannella vermiformis, another protozoan that behaves much like Acanthamoeba with respect to harboring and protecting microbial pathogens, has been identified in water as well.17

Biofilm is an elaborate matrix of polysaccharides derived from heterogeneous populations of bacteria that protects them from caustic agents by serving as a barrier to the penetration of biocides.18-19 Biofilm is the slime that you can easily detect on the glass inside a fish tank, and it is also the slippery coating found on rocks in a stream. Biofilm lines the pipes of virtually all plumbing systems, and unless remedial measures are taken to eradicate it, biofilm will persist and act as a repository for the continuous release of bacteria within the water supply. Within a biofilm community, microorganisms are relatively resistant to the presence of disinfectants, unless the concentration of such agents is maintained at adequate levels so that diffusion into the biofilm will reach the microbes.20 However, it is difficult to maintain effective levels of antimicrobial agents because water flow varies from one tap to the next. Less frequently used, therefore, taps often release higher levels of bacteria upon the initiation of flow.

Recently, Acanthamoeba has been shown to be capable of harboring, without killing, Legionella, Mycobacterium and Pseudomonas aeruginosa, all waterborne pathogens of clinical significance.21 Acanthamoeba is capable of surviving in the presence of many systemic disinfection agents.22 Consequently, the pathogenic microbes harbored by Acanthamoeba may emerge unharmed from its protective shield when the outside environment is less hostile, thereby putting patients at risk for infectious complications. Clearly, there is need for a complementary infection control strategy, and point-of-use water filtration holds that promise.23

The Centers for Disease Control and Prevention (CDC) has identified, as an alternative to sterile water, 0.2 µm filtered water to meet the standard of the highest quality of water that is practical for final rinse of endoscopes and other medical devices.24-25

In the context of hospital water filtration, 0.2 µm filters are being used with success. In a pediatric nephrology unit, a retrospective investigation revealed several cases of Legionella infection due to Legionella pneumophila serotype 6, which was identified in hospital water limited to that unit. Clinicians subsequently elected to implement point-of-use water filtration as part of their infection control strategy after determining that the installation and maintenance of filters were cost permissive.26

Hummel and co-workers27 used point-of-use water filters as part of an infection control strategy to minimize exposure to Legionella serogroup 1 in a heart transplant unit. Legionella had been determined to be refractory to conventional sanitation treatments. The incidence of Legionella infection confirmed by urine antigen testing approximated 23 percent before point-of use water filters were installed. After filter installation, as part of the infection control strategy, the rate dropped to 15 percent and it was further reduced to 1.9 percent when the additional measures of Legionella urinary antigen screening and the appropriate use of antibiotics were implemented.

Vonberg and co-workers in Hannover, Germany evaluated the performance of 0.2 µm point-of-use tap water filters in three intensive care units involving 767 samples.28 Without filtration, it was shown that 30 of 32 samples collected were positive for Legionella at concentrations ranging from 1 to 106 CFU/mL. In contrast, 255 out of 256 samples recovered from taps fitted with filters for seven days failed to yield any Legionella upon culture. In the only positive sample obtained, a Legionella concentration of 1 CFU/mL was observed.

Application of point-of-use filters on faucets and showerheads became part of an infection control program in response to an outbreak of six cases of P. aeruginosa (two pneumonias, two septicemias, and two wound infections) in an adult hematology/ oncology unit at the University of Bonn in Germany.29 A survey of 209 environmental samples revealed contamination in surface cleaning equipment, taps, sink drains and showers. After implementation of point-of use water filters, the healthcare-acquired infection (HAI) rate reverted to pre-outbreak levels. More recently, similar success in the reduction of serious Pseudomonas infections following implementation of point-of-use water filtration was reported in a non-outbreak setting in yet another hematology/oncology unit.30

Despite claims to the contrary, not all filters are alike,31 and confidence in their use should be based upon performance claims and actual clinical use experience.

The inadequacy of water treatment standards is being recognized.32 A greater appreciation is developing for the dangers of waterborne microorganisms that survive within, and are released from, the protection of biofilm.33-35 Although drug therapies are being developed to target biofilm, the emergence of drug resistance is a persistent concern.36-38 Increasing recognition of the role that Acanthamoeba, a common waterborne protozoan, plays in protecting bacteria from sanitation methods, thus increasing the likelihood of passing on the more virulent strains of pathogens, contributes to mounting concern as well.

Finally, the value of microbial protection barriers afforded by 0.2 µm filtration at the point-of-use is gaining momentum, with increasing numbers of studies illustrating the benefits of its use. These technologies are available and can be implemented easily and cost-effectively to protect vulnerable patients in healthcare settings.

Girolomo A. Ortolano, PhD, and Frank P. Canonica, PhD, are with Pall Medical; Joseph S. Cervia, MD, is with Pall Medical and Einstein College of Medicine in New York.


References

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