What specific organisms pose a risk for patients by/in water?

Hospital water is an important and controllable source of hospital acquired infection.

Potential routes of infection from hospital water

Ingestion (drinking) leading to gastrointestinal infections:

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  • Bacteria such as Campylobacter spp., Escherichia coli, Salmonella spp., Shigella spp., Vibrio cholerae, and Yersinia spp.

  • Viruses such as Adenovirus, Enteroviruses, Hepatitis A, Norovirus, and Rotavirus.

  • Protozoa and helminths such as Cryptosporidium, Dracunculus medinensis, Entamoeba histolytica, Giardia intestinalis, and Toxoplasma gondii.

Inhalation and aspiration (aerosols) leading to respiratory infections:

  • Bacteria such as Legionella pneumophila.

  • Non-tuberculous mycobacteria.

  • Protozoa such Naegleria fowleri.

Contact (bathing) leading to infections of the skin, wounds, and mucous membranes:

  • Bacteria such as Aeromonas spp. Burkholderia spp., Leptospira spp., and Pseudomonas aeruginosa.

  • Protozoa such as Acanthamoeba spp.

  • Trematodes (flukes) such as Schistosoma mansoni.

What is the impact of such infections if not prevented?

The existing body of literature on waterborne infections in the hospital suggests that the associated morbidity and mortality are significant. Anaissie et al. estimated that 1400 deaths occur annually in the United States from hospital acquired waterborne pathogens, in particular P. aeruginosa.

Numerous outbreaks have been linked to contaminated water (Table I).

Table I.
Organism Reservoir Infection
Pseudomonas paucimobilis Water bottles for tracheal suction Pneumonia
Serratia marcessans Water humidifiers Pneumonia
Mycobacterium xenopi Hot water taps Pneumonia
Mycobacterium chelonae Contaminated equipment Otitis
Legionella pneumophila Hospital water, cooling towers Pneumonia
Acinetobacter spp. Water bath used to thaw fresh plasma Bacteremia
P. aeruginosa Water bath used to thaw cryoprecipitate, hospital water Bacteremia, pneumonia
P. aeruginosa Tub water contamination Folliculitis, skin infections
Clostridium difficile Bath Diarrhea
Stenotrophomonas maltophilia Hospital water Bacteremia
Cryptosporidium Hospital water Diarrhea

Table adapted from Guide for Infection Control in the Hospital, 2008 International Society for Infectious Diseases.

What are the key methods to minimize transmission of infection to patients by/in water?

Although it is well established that water plumbing systems and faucets are reservoirs are for pathogens, especially Legionella and P. aeruginosa, an international consensus for the prevention and control of water acquired hospital infections has yet to be developed.

The following practices apply to the prevention of infection via hospital water sources:

  • Clinician epidemiologists must have a high level of suspicion for cases of water borne infections in particular if clusters of infection are identified with signature organisms.

  • Water used for dialysis should be sampled regularly on a monthly basis. Acceptable levels of contamination are less than 200 bacteria/mL.

  • Dialysate should be cultured, and bacteria must be less than 200/mL.

  • When rinsing nebulization devices and semi-critical care equipment, sterile water should be used.

  • Chlorination of hospital water should be tested periodically. Testing should occur in the incoming tap water. In addition, the entire hospital system, including areas housing immunocompromised patients should be tested.

  • Hospital tap water should not be given to immunosuppressed patients. Instead, sterile/filtered water should be provided.

  • Cooling towers should be directed away from the hospital’s air intake system. The cooling towers should be designed such that the volume of the aerosol drift is minimized. Cooling towers should have drift eliminators installed, and a biocide should be used in accordance with the manufacturer’s recommendations.

What data support current recommendations with respect to water?

Complete prevention of waterborne pathogens in the hospital water system may not be fully attainable; however, the risk can be minimized by filtration and disinfection.

The control of biofilms is critical for the prevention and control of waterborne pathogens in the hospital water supply. Given that biofilms are difficult to eradicate once established, prevention of their formation is of paramount strategic importance.

To minimize the development of biofilms, hospitals must limit the level of free-floating bacteria in the water supply and perform reliable and continuous disinfection of the water supply.

The following are evidence based strategies for the control of biofilms in hospital water supply:

  • Continuous application of low concentrations of disinfectants and ultraviolet (UV) radion can prevent the formation of biofilms in hospital plumbing.

  • This strategy includes:

    Copper-silver ionization.

    Chlorine dioxide.

    UV light disinfection.

A crucial point is that effective disinfection systems must be in operation at the onset of water flow into the hospital plumbing system. If biofilms are already present in the hospital plumbing system, eradication proves exceedingly difficult.

In this scenario, the use of UV light irradiation, in particular, as a means of hospital water disinfection, will have minimal impact on biofilm eradication.

Attention must also be paid to the quality of water at the point of use. Specifically, the application of sterile, point of use filters on faucets and shower heads is supported by the literature, particularly for the control of Legionella and P. aeruginosa infections.

In high-risk areas, such as transplant units and intensive care units (ICUs), the installation of point-of-use filters on faucets and shower heads was proven to be effective for the prevention and control of waterborne pathogens.

Point of use filters are also helpful for the control of fungi, protozoa, and non-tuberculous mycobacteria. Thus, to protect high risk patients, it is recommended that point of use filtration systems be installed in high-risk units.

The use of sterile water for high risk patients is recommended by some authorities. However, this approach may be costly. Sterile bottled water is more expensive than water filtered with point of use filtration systems.

Particular attention should be paid to the control of Legionella in water systems and several strategies are reported for its control.

These include thermal eradication (heat and flush – 30 minute flushes of distal outlets with water at 70 degrees Celsius), hyperchlorination, copper-silver ionization, point of use filters, chlorine-dioxide, and UV light disinfection. A recent article published by Marchesi et al. suggests that the use of chlorine dioxide in parallel with electric boilers may be the most effective strategy for the control of Legionella.

Despite aggressive measures, it should be noted that compete eradication of Legionella may not be feasible.

It is documented that new pipes in the distribution system of water utilities can be sources of P. aeruginosa. As a result, new pipes should only be put to use when P. aeruginosahas not been detected in the water by sampling (0 CF U /100mL water).

The disinfection methods used to control organisms such as Pseudomonas, Burkholderia, Enterobacter, and Acinetobacter spp. along with other gram negative rods are the same as those implemented for the control of Legionella (Table II).

Table II.
Organism Strategy
Legionella species


Copper-silver ionization

Point of use filters


UV light disinfection

Chlorine dioxide in parallel with electric boilers

Thermal eradication

Acinetobacter spp. and other gram negative rods


Copper-silver ionization

Point of use filters


UV light disinfection

Chlorine dioxide in parallel with electric boilers

Thermal eradication


Point of use filters


Point of use filters


Point of use filters

How can the safety of water be monitored? At what frequency?

Environmental water culturing provides important information about potential contamination of the plumbing system with waterborne pathogens. In addition, culturing of the hospital’s water source permits verification that the prevention and water quality control systems are operating optimally.

The routine use of environmental cultures has emerged as an effective strategy for the prevention of hospital-acquired Legionnaires’ disease. If Legionella colonization of the water supply is recorded, physician index of suspicion for Legionnaires’ disease should be heightened.

The Centers for Disease Control (CDC) recommends environmental cultures only in the event that hospital-acquired Legionnaires’ disease is discovered. Many European countries, including England, Wales, Switzerland, and Spain have adopted this approach.

Routine surveillance can be performed using either swab or water samples. The swabs should sample the biofilm. For example, swab samples should be collected first, after removal of the faucet aerator. This should achieve maximal recovery of Legionella from the biofilm within the fixture. If aerators are not removed, biofilm may not be adequately sampled, and the outcome can be a false negative result.

If a case investigation is underway, then the goal of sampling is to maximize sensitivity. In this scenario, water and swab samples should be collected from the water outlets in the immediate environment of a suspected case or throughout the high-risk hospital unit in question.

The above approach to environmental Legionella sampling typically requires water and biofilm sampling in the hot water recirculating line and at the point of care water outlets. This method can be labor intensive and time consuming, especially if employed routinely for surveillance purposes.

However, a recently published paper suggests that hospitals can safely adopt a more efficient and simpler environmental sampling policy for Legionella. This method would include water sampling only – without biofilm sampling – and a more efficient monitoring of the entire system through sampling of recirculation loop water.

Water used for dialysis should be sampled regularly on a monthly basis. Acceptable levels of contamination are less than 200 bacteria/mL. From an infection prevention perspective, water safety in dialysis focuses on minimizing patient exposure to endotoxins and bacterial fragments.

As such, each renal unit should have standard operating procedures in place for sampling, monitoring, and recording of the water feed (raw, untreated water entering the water treatment plant) and product water quality.

To minimize the development and growth of a biofilm, a strict strategy of proactive preventive measures should be adopted. Successful strategies include the use of filters for water entering the distribution loop, the installation of filters on each dialysis machine, and weekly microbiological monitoring of the distribution system. Additionally, routine heat disinfection using hot water (>80 °C) for a minimum of 120 minutes is performed every 2 weeks in some facilities.

At present, more information is necessary concerning the consequences of water contamination by fungi, non-tuberculous mycobacteria and amoeba. No standard surveillance protocol exists for these pathogens.

What are the controversies related to hospital management of water?

Areas of ongoing controversy with respect to hospital water include the use of sterile water for ALL patients and routine culturing of hospital water for Legionella.

The eradication of Legionella from hospital water systems remains a challenge. Despite numerous and varied strategies for the control and elimination of Legionella from hospital water, once present, eradication is typically transient, with no single strategy emerging as clearly the most effective.

The acceptable microbiologic count in dialysate has not been standardized and differences exist between Europe and the United States.

What data support each side of the controversies?

Sterile water

Hall and colleagues performed an extensive analysis of water quality across numerous health trusts in the United Kingdom. Using the criteria of cost, microbiological quality, and patient satisfaction, the authors concluded that end-line filtration represents the best option provided that protocols exist for the replacement of filter cartridges at the appropriate times.

This approach was cost effective, cheaper than sterile, bottled water, and would diminish the risk of cryptosporidiosis and exposure to environmental bacteria such as Pseudomonas and atypical mycobacteria.


The need for sampling hospital water routinely to detect Legionella outside of outbreaks, i.e., as a component of primary prevention, is unclear.

The data are mixed, and these differences are likely due to heterogeneous patient populations studied, methods of laboratory diagnosis of clinical cases, the analysis of hospital water, and differences in the design of hospital water systems.

For hospitals with immunocompromised patients, such as solid organ and bone marrow transplant units, routine sampling for Legionella in hospital water should be considered.

The eradication of Legionella is problematic. Different strategies have been suggested but none are fully successful.

Strategies include engineering modifications, heating the water to temperatures above 59 degrees Celsius, heating and flushing the plumbing with hot water (80 degrees Celsius), water chlorination, silver-copper ionization, and UV light disinfection of water.

A current publication suggests that chlorine dioxide in parallel with electric boilers may be superior to other strategies for the control of Legionella. While this is promising, this finding must be reproduced by other investigators and in other hospital settings prior to universal acceptance.


Current standards differ only slightly in the maximum levels of bacteria allowed in dialysis water; however, there are important differences in the methods used to determine those levels.

In particular, the combination of culture medium, incubation time, and incubation temperature specified in the United States standard yields significantly lower levels of bacteria than those obtained using the conditions specified in the European Renal Association’s Best Practice Guidelines. Prospective randomized trials are lacking to define the optimal approach for dialysate water sampling.

What guidelines are currently in place?

The following organizations provide guidance for water quality in healthcare facilities:

  • CDC: Guidelines for Environmental Infection Control in Healthcare Facilities.

  • Association of Professionals in Infection Control (APIC): Guidelines for Environmental Infection Control in Healthcare Facilities.

  • World Health Organization: The Hospital Environment and Hospital Associated Infections.

  • CDC: Water Use in Hemodialysis.

  • European Renal Association: Best Practices Guidelines for Hemodialysis.


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