Water distribution systems in large buildings frequently contain biofilm which is difficult to eradicate once established.
Immunocompromised people are especially susceptible to an increased infection risk for waterborne pathogens such as Pseudomonas aeruginosa, Legionella pneumophila, Non-Tuberculosis Mycobacteria, fungi and other microorganisms. Water filtration, directly at the point-of-use, is increasingly used to establish efficient barriers against transmission of waterborne pathogens from water sources to consumers.
Well-controlled and hygienically safe water is delivered from water plants to cities. During its transport water is cold and flows continuously through large diameter pipes. However, this situation changes dramatically at the point of entrance to buildings1,2. Within buildings water stagnates and its temperature increases. It passes through complex internal distribution systems consisting of narrow pipes with possibly corroded inner surfaces and dead ends. This environment provides optimal conditions for the formation of biofilm from which bacteria and other microorganisms are continuously released into the water3-5.
Biofilm forms when planktonic bacteria come into contact with a conditioned surface (e.g. the inner surface of a water pipe). They produce extracellular polymeric substances (EPS) that anchor them to the surface. In water distribution systems biofilm can develop within a few days even if the water meets drinking water criteria2. The EPS can host bacteria, amoeba, algae and other microorganisms. Under low flow conditions, such as in dead legs, particularly thick biofilms can form. Under the force of water flow biofilm shears off and biofilm particles can colonize other parts of the water distribution system3. External physical stress in the pipework, e.g. through disinfection measures , can result in an increased expression of the biofilm phenotype cell which is responsible for the strong attachment of cells to a surface5.
With increasing thickness, biofilm better protects the microorganisms inside from chemical agents and thermal disinfection procedures2,5. It is therefore 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 cells3.
The majority of bacteria in a common water pipework live within biofilm (about 95%) and only about 5% occur in the water phase4,6. Biofilms contain a large variety of waterborne microorganisms. These include protozoa (e.g. Acanthamoeba), fungi (e.g. Aspergillus spp.), viruses and a number of human pathogenic bacteria1,3-6. 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., and Klebsiella spp.3-6. Legionella pneumophila is perhaps the best-known bacterium colonizing biofilm, and it can be found in both central storage areas (e.g. water tanks) as well as peripheral water outlets2,3,5. Waterborne Pseudomonas aeruginosa is a major cause of severe infections7-9.
The Viable But Non-Culturable (VBNC) cell fails to grow on routine bacteriological culture media, but is alive and capable of renewed metabolic activity - indeed it can be "resuscitated" to a culturable state with renewed virulence6,10-12. This discovery has thrown the accuracy of quantifying culturing techniques into question. It is understood that a high proportion of biofilm dwelling cells lives in the VBNC state and that the VBNC state can be induced by antibacterial material such as copper pipes11 as well as by thermal treatments12. As water pathogens such as P. aeruginosa in their VBNC state are not detectable by standard culture methods, alternative diagnostic technologies such as Polymerase Chain Reaction (PCR) or Fluorescence In Situ Hybridization (FISH) are required in order to confirm their presence6.
Amoeba are very important hosts for water bacteria. L. pneumophila, Mycobacteria spp. and other “amoeba resistant bacteria” can be safely carried by these protozoa13,14. Legionella are taken up into amoeba without being digested and replicate there within vacuoles. When the Legionella have reached a certain density, the vacuoles release them into the water system14.
Pseudomonas aeruginosa is one of the most problematic bacteria in health care facilities and is responsible for about 10-20% of HAIs in Intensive Care Units (pneumonia, wound infections, blood stream infections and urinary tract infections)8. Several studies have shown that up to 50% of the hospital acquired P. aeruginosa infections may be derived from the water distribution system15-17. P. aeruginosa is increasingly recognized as a potentially problematic water pathogen outside of hospital settings. Infection chains from water taps to people have been reported. P. aeruginosa easily colonizes all kinds of fluids (even distilled water) and rapidly forms biofilms8. P. aeruginosa strains have developed resistance against commonly used antibiotics, rendering effective treatment increasingly complicated and expensive18. 
Inhalation and aspiration represent transmission pathways for Legionella spp. Pseudomonas spp. can be transmitted by contact and aspiration. 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 of entry represent potential entrance sites for bacteria. Droplets of contaminated tap water or contaminated hands of nursing staff can inadvertently come into contact with those entrance sites. Rogues et al. reported that 14% of ICU (Intensive Care Unit) health care workers hands were Pseudomonas positive when washed with contaminated tap water and 12% were positive when the last contact was with a Pseudomonas positive patient19. Contaminated bottled water or contaminated water from drinking water dispensers has also been described as a source of hospital-associated Pseudomonas infections in ICUs and Bone Marrow Transplantations (BMTs)20,21.
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, insufficient temperature below 55°C in the hot water pipes and above 20 °C in the cold pipes contribute to biofilm formation and make complete eradication of biofilm hardly possible. Heat & flush procedures (10-20 minutes of simultaneous flushing of all outlets with water heated to > 70 °C) may have only short term effects22. Legionella strains may even become heat resistant after thermal treatment over a long time12. Thermal procedures can result in warming up cold water 23 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 use22,24,25.
Therefore, areas with immunosuppressed people require additional protection (e.g. point-of-use water filtration) to minimize transmission of waterborne pathogens to patients.
Point-of-use water filters are used as an additional safety measure in those areas where highly immunocompromised people come into contact with water26-43 and in outbreak situations. They can be flexibly installed at faucets (tap filters) or connected to shower hoses (shower filters). In medical facilities most common areas include bone marrow transplant units, hematology/oncology units, intensive care units, transplantation units, burn units, neonatology, endoscopic reprocessing, birth tubs, kitchen (for food preparation for critical patients), and geriatric departments. Based on the clinical experiences POU water filtration is also increasingly used in other areas with immunocompromised patients such as nursing homes or home care settings. Those end point filters are quickly installed which makes them also a useful instrument in acute outbreak control e.g. in public buildings, apartment houses, swimming pools, sports centers or hotels.
POU filtration delivers water filtered in accordance with international standards (retention of ≥107 Brevundimonas diminuta/cm2 filtration media surface)44. Since end point filters are mostly used in a humid environment a risk of contamination of the filter housing exists through backsplash. In order to minimize this risk of retrograde contamination, Pall POU water filters contain a non-leaching, bacteriostatic additive throughout the housing polymer. Hygienic safety of these POU filters has been demonstrated through laboratory validation, multicentre field evaluations, and independent clinical studies26-43.
In order to make filter exchange record-keeping easier, Pall POU water filters are equipped with peelable, writable labels for recording filter exchange information. The exchange can also be monitored electronically using a specific software package (Pall-Aquasafe Data) to deliver an audit traceable trail of filter exchange45. Easy filter replacement within seconds is guaranteed using quick connectors that are tailored to the filters. Integrated pre-filtration helps to maintain high flow rates over the filter lifetime. Pall POU water filters are compatible with systemic treatments like continuous heating (at 60°C), heat and flush procedures (at 70 °C) or chlorine dioxide disinfection. Since POU filtered water is also used as drinking water, filters must fulfill drinking water requirements.
World Health Organisation (WHO) recommendations are generally followed throughout the world for drinking water quality requirements and point-of-use water filtration is listed in those recommendations as one measure in hospital risk areas1,50. In addition there are numerous national and regional drinking water guidelines, and several have integrated POU filtration as one option to prevent transmission of water pathogens to patients and users. Since 2002, a guideline from the French Ministry of Health has advised that healthcare facilities install 0.2 µm micro-filtration at point-of-use in high risk areas46. The Robert Koch Institute (RKI) recommends water filtration during the last rinsing step of endoscopic reprocessing protocols47. In 2010 the German Committee for Hospital Hygiene & Infection Prevention at the RKI recommended point-of-use water filters for specific applications in the care of highly immune-compromised patients48. In the UK, the Yorkshire Cancer Network states that point-of-use filtered water is the most appropriate option for the provision of potable water for immuno-compromised cancer patients49. In the WHO publication “Legionella and the prevention of Legionellosis” (2007) point-of-use filters are recommended for high risk areas such as transplant units and ICUs when Legionella free water (0 CFU/1000 mL) is not achievable50. More examples regarding filter recommendation are from Canada and Australia for endoscope reprocessing51,52.
Numerous reports have demonstrated the high efficiency of Pall’s POU water filters under clinical conditions26-42. In several studies a reduction of waterborne infection/contamination rates have been documented after installation of Pall-Aquasafe filters. Vianelli et al. (2006) reported that the use of disposable filters during a Pseudomonas aeruginosa outbreak in a hematology unit resulted in a highly significant reduction of both colonizations and infections26. Van der Mee-Marquet et al. (2005) documented a reduction in pulmonary, bloodstream and urinary P. aeruginosa infections from 8.7/1000 patient days (before filtration) to 3.9/1000 patient days (after filtration)27. The reduction of infections from multisensitive P. aeruginosa isolates (most probably derived directly from the water) was particularly pronounced. Trautmann et al. (2008) reported on endemic P. aeruginosa infections on a surgical ICU29. Various measures such as regular change of aerators or use of bottled sterile water for oral hygiene did not result in a significant reduction of Pseudomonas positive patients. In contrast the comparison between 12 months pre-filter (n = 649 patients) and filter periods (n = 585 patients, 12 months) revealed a significant reduction of infections by 56% (p<0.0003) after installation of disposable POU water filters29. Also a reduction of nosocomial P. aeruginosa infections in burn patients from 10% to 2.5% and a 50% reduction of Gram negative bacteria infections in a bone marrow transplant unit in the US have been reported after installation of Pall-Aquasafe filters30,42.
More recently other investigators in the US, Asia and Europe have confirmed the efficacy of Pall-Aquasafe water filters as a barrier for transmission of waterborne pathogens in healthcare settings31-42.
Cost comparisons between sterile bottled water, commercially available mineral water and POU filtered water provided as drinking water for highly immunocompromised patients in hospitals revealed significant cost advantages of disposable point-of-use filters28. For example hospital acquired waterborne infection results in higher morbidity, mortality and adds costs to healthcare facilities. The value of POU filtration must therefore also be assessed from a preventive perspective. P. aeruginosa for example is known to cause hospital acquired infections in intensive care units such as bloodstream infections, urinary tract infections, surgical wound infections and pneumonia8. Additional costs for bloodstream infections or pneumonia in ICU patients can easily exceed 15,000 USD per patient53-56. Installation of POU water filters in one ICU with 10 water taps may reveal cost savings if only one single infection is avoided. Indeed, in a large clinical study significant cost savings of about 64,000 USD per year were calculated after installation of disposable water filters on 7 ICU taps per year based on the reduction of Pseudomonas infections29. In another study, net cost savings of 231,000 USD due to the reduction of total patient care cost after filter installation have been reported in a subacute care unit in the US (2010)41. One additional way to save cost using Pall’s POU water filters has been demonstrated by installing filters in the laboratory setting to avoid false positive Tuberculosis fast acid staining results deriving from Non-Tuberculous Mycobacteria in the rinse water57. The cost saving per avoided false positive result was approximately 2,250 USD.
