Potable Water Systems in Health Care Facilities

Biofilm protects the microorganisms within from chemical agents and thermal disinfection procedures (2,5). It is extremely difficult to completely eradicate the biofilm community once established. Irregular shedding from a biofilm can result in significant deviations of bacterial counts at sampling sites or points-of-use (POU) (2-4). Bacteria within biofilm communities have been shown to exhibit greater resistance against antimicrobial treatments than corresponding planktonic cells (3). 

The majority of bacteria in a water pipework live within biofilm (about 95 %) and only about 5 % occur in
the water phase (7). Biofilms contain a large variety of waterborne microorganisms (91-93). These may include protozoa (e.g. Acanthamoeba), fungi (e.g. Aspergillus spp., Fusarium spp.), viruses and a number of human pathogenic bacteria (1,3,5,7-9). Among those bacterial species found in biofilm that are potentially harmful for immunocompromised people are Pseudomonas aeruginosa, non-tuberculous Mycobacteria, Stenotrophomonas maltophilia, Acinetobacter baumanii, Chrysobacterium spp., Sphingomonas spp., Aeromonas hydrophila, Simkania negevensis, Elizabethkingia meningoseptica and Klebsiella spp. (3,5,7,10-13). Legionella pneumophila is perhaps the best-known waterborne bacterium colonizing biofilm, and it can be found in both central storage areas (e.g. water tanks) as well as peripheral water outlets (2,3,5). Pseudomonas aeruginosa is known to be a major cause of severe infections (14-17), including pneumonia, sepsis, wound and skin infections. 

The Viable But Non-Culturable (VBNC) cell fails to grow on routine bacteriological culture media, but is alive and capable of metabolic activity - indeed it can be “resuscitated” to a culturable state with renewed virulence (6, 18-21). This discovery has thrown the accuracy of quantifying culturing techniques into question. It is understood that a high proportion of biofilm dwelling cells live in the VBNC state and that the VBNC state can be induced by antibacterial material such as copper pipes (19), stress factors like starvation, exposure to temperatures outside the range of growth or exposure to chemical and thermal treatments (20-26). As water pathogens such as P. aeruginosa and L. pneumophila in their VBNC state are not detectable by standard culture methods, alternative diagnostic technologies such as Polymerase Chain Reaction (PCR), Fluorescence In Situ Hybridization (FISH) or determination of total cell number (TCN) are required in order to confirm their presence (6, 27). L. pneumophila, P. aeruginosa, Campylobacter jejuni and other waterborne bacteria have also been shown to be resuscitated to culturable cells under suitable stimuli (21, 28, 29). 

Amoeba are very important hosts for water bacteria. L. pneumophila, Mycobacteria spp. and other “amoeba resistant bacteria” can be carried by these protozoa (9, 30-34). Legionellae are taken up into amoeba without being digested and replicate there within vacuoles. When the Legionellae have reached a certain density, the vacuoles release them into the water system (31). Amoeba not only function as environmental reservoirs for Legionella, but have been also shown to be involved in selecting for, protecting and maintaining potentially pathogenic Legionella spp. in the environment (35, 36). 

Pseudomonas aeruginosa is widely reported as one of the most common and problematic bacteria in health care facilities (15, 37). Several studies have shown that up to 50% of hospital acquired P. aeruginosa infections may be derived from the water distribution system (15, 17, 38-44, 48). 

Inhalation and aspiration represent the established transmission pathways for Legionella spp. (49), whereas Pseudomonas spp. is reported to be mainly transmitted by contact and aspiration (17, 41). During daily routines, tap water is used for personal hygiene. For example, in the healthcare environment, due to the severity of their disease states, ICU patients often have multiple access devices such as catheters, drains and tracheal tubes. These portals represent potential entrance sites for bacteria from numerous sources. Droplets of contaminated tap water or contaminated hands of healthcare professionals can inadvertently come into contact with those entrance sites (50). Rogues et al. reported that 14 % of ICU healthcare professionals hands were Pseudomonas positive when washed with contaminated tap water and 12 % were positive when the last contact was with a Pseudomonas positive patient (41). Contaminated bottled water or contaminated water from drinking water dispensers has also been described as a source of Pseudomonas bacteria (51-53). 

Water distribution systems in large buildings are frequently complex networks and can be up to 50 km in length. Dead ends, corroded pipes, low throughput, insuf cient temperature below 131 °F (55 °C) in the hot water pipes and above 68 °F (20 °C) in the cold pipes contribute to biofilm formation and impede eradication of biofilm (54). Heat & Flush procedures (e.g. 10-20 minutes of simultaneous  flushing of all outlets with water heated to > 158 °F (> 70 °C) may have only short term effects (55). Legionella strains may even become heat resistant after thermal treatment over a long time (20). Moreover, the thermophilic Legionella community, including L. pneumophila, is able to grow in hot water system above 122 °F (50 °C) (56). Thermal procedures can result in warming up cold water (26, 57, 58), when both hot and cold water pipes are located in the same duct increasing the risk of biofilm in cold water. Chemical treatments are bactericidal to free floating bacteria but have limited effects on biofilm and may create hazardous byproducts during use (10, 55, 59, 60). Therefore, areas with vulnerable users may require additional protection (e.g. 0.2 μm point-of-use waterfiltration) to minimize risk of transmission of waterborne pathogens. 

Point-of-use water filters can be used as an additional control measure in those areas where immunocompromised people may come into contact with water (61-85), in outbreak and critical contamination solutions as an aid in reducing patient exposure. They can be exibly installed at faucets (tap filters) or connected to shower hoses (shower filters). In medical facilities the most common areas for POU water filter installation are bone marrow transplant units, hematology/oncology units, ICUs, transplantation units, burn units, neonatology, endoscopic reprocessing, birthing pools, kitchen (for food preparation and drinking water provision), and geriatric departments. POU water filtration is also increasingly used in nursing homes or home care settings POU filters are quickly installed which makes them an effective and immediate management tool in acute water contamination situations. 

User facilities typically ask for POU filtration designed to deliver water quality in accordance with international standards for sterilizing grade filtration (complete retention of ≥107 CFU Brevundimonas diminuta/cm2 effective filtration area) (87-90). End point filters are mostly used in humid environments, and the risk of contamination of the filter housing exists through backsplash. In order to minimize this risk of retrograde contamination, Pall POU water filters contain anti-retrograde contamination technologies. Hygienic performance of these POU filters has been demonstrated through laboratory validation, multicentre field evaluations, and independent clinical studies demonstrating robust performance over the full product lifetime (61-85). 

Numerous reports have demonstrated the high efficiency of Pall’s POU water filters in the retention of microoganisms from water outlets in clinical locations and conditions (17, 28-49, 61-86).