Controlling and Preventing Air- and Waterborne Infections

Pathogenic microorganisms are transmitted in numerous ways in hospitals. One important consideration is the role that the environment plays in pathogen transmission, specifically leading to airborne and waterborne infections.

By Kelly M. Pyrek

Pathogenic microorganisms are transmitted in numerous ways in hospitals. One important consideration is the role that the environment plays in pathogen transmission, specifically leading to airborne and waterborne infections.

Airborne Pathogens

As Ulrich, et al. (2004) note, "Evidence from many studies leaves no doubt that hospital air quality and ventilation play decisive roles in affecting air concentrations of pathogens such as fungal spores (Aspergillus) and, in this way, have major effects on infection rates. Well-conducted research has linked all of the following to air quality and infection rates: type of air filter, direction of airflow and air pressure, air changes per hour in room, humidity, and ventilation system cleaning and maintenance."

Joseph (2006) explains that airborne pathogens are transmitted in three ways:

- When an environmental reservoir of a pathogen is disturbed, fungal spores may be released into the air and make their way into the hospital environment.

- Microorganisms can also be transmitted directly from person to person in the form of droplets in the air produced by coughing or sneezing within three feet to six feet

- Other infectious diseases such as tuberculosis are transmitted via residuals of droplets that remain indefinitely suspended in the air and can be transported over long distances.

Sources of airborne pathogens are numerous and include:

- Construction and renovation activities

Airborne pathogens such as Aspergillus survive in the air, dust and moisture present in healthcare facilities and are usually released into the air during site construction and renovation.

- Ventilation system contamination and malfunction

Studies have identified the type of air filter, direction of airflow and air pressure, air changes per hour in room, humidity and ventilation-system cleaning and maintenance as factors related to air quality and infection rates. Accumulation of dust and moisture within HVAC systems increases the risk for the spread of environmental fungi and bacteria.

- Vectorborne transmission via pigeon droppings or insect/rodent droppings

Healthcare policies must appropriately address engineering controls for airborne disease, and they must educate and train these workers on the Occupational Safety and Health Administration (OSHA)s hierarchy of administrative, engineering and personal protective equipment (PPE) for protection in AIIRs, according to Paul Ninomura, PE, chairman of the Project Committee for Standard 170 Ventilation of Healthcare Facilities of the American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc. (ASHRAE).

Some areas of the hospital such as the operating room (OR) or the emergency department (ED) -- are especially vulnerable to movement by healthcare workers that could stir up infectious microorganisms and particulates. Ninomura and Judene Bartley, MS, MPH, a member of ASHRAEs Standard 170 Committee, add that when designed in accordance with ASHRAE Standard 170, the OR is a clean area with clean filtered air supplied in a unidirectional airflow from the ceiling to the operating room table. The design utilizes low velocity airflow to minimize turbulence that may occur as surgeons and staff work within the airflow in the operating room. ED waiting rooms have relatively high air exchange rates, and have requirements that all air is exhausted outside, providing a dilution ventilation strategy that controls the propagation of infectious agents from undiagnosed patients with airborne infectious disease.

As Joseph (2006) notes, "The importance of good air quality in controlling and preventing airborne infections in healthcare facilities cannot be overemphasized. Providing clean filtered air and effectively controlling indoor air pollution through ventilation are two key aspects of maintaining good air quality."

Airborne infections can be controlled and prevented by use of the following:

- HEPA filtration

The control of microorganisms and other pollutants and particulates at the source is the most effective way to maintain clean air. Filtration, which is the physical removal of particulates from air, is a key step toward achieving acceptable indoor air quality. HEPA filters are at least 99.97 percent efficient for removing particles 0.3 m (as a reference, Aspergillus spores are 2.5 to 3.0 m in diameter), and their efficiency can be increased to 99.99 percent where needed.

 - Ventilation

After filtration, the second most effective way of controlling the level of pathogens in the air is through ventilation. Ventilation guidelines are defined in terms of air volume per minute per occupant and are based on the assumption that occupants and their activities are responsible for most of the contaminants in the conditioned space. Most ventilation rates for healthcare facilities are expressed as room air changes per hour (ACH). Peak efficiency for particle removal in the air space occurs between 12 ACH and 15 ACH. Ventilation rates vary among different patient-care areas of a healthcare institution and ventilation standards are provided in guidelines from the American Institute of Architects or the American Society of Heating, Cooling and Air-conditioning Engineers (ASHRAE).

According to Ninomura, ASHRAE Standard 170 should be a primary reference along with the FGI Design and Construction of Health Care Facilities when designing a new facility. ASHRAE Standard 170 addresses the removal of airborne pathogens through a combination of filtration, the direct exhaust of contaminated air and dilution via introduction of outdoor air.

Waterborne Pathogens

One of the most important waterborne pathogens in the hospital environment is Legionellosis, the infection produced by the pathogen Legionella, a bacterium found in water environments. Many hospital water systems are colonized with legionellae, which is introduced into institutional water distribution systems from municipal water systems that do not routinely screen water for the presence of Legionellae.

According to Joseph (2006), waterborne microorganisms proliferate in moist environments and aqueous solutions, especially under warm temperature conditions and presence of a source of nutrition. Waterborne infections spread through direct contact (such as during hydrotherapy), ingestion of contaminated water, indirect contact and inhalation of aerosols dispersed from water sources.

Transmission of Legionella includes inhalation of airborne droplets from bacteria from showers, faucets, room-air humidifiers, cooling towers, evaporative condensers, decorative fountains and medical equipment such as nasogastric tubes and bronchoscopes that are rinsed with contaminated tap water. Immunocompromised patients are most at risk to this bacterium, and the factors that enhance colonization and amplification of legionellae are warm water, water stagnation, and sufficient food for bacteria, including scale, sediment and biofilms.

The Centers for Disease Control and Prevention (CDC), in its Guideline for Environmental Infection Control in Healthcare Facilities, advises following special infection control measures for settings providing care to immunosuppressed patients so that aerosol production is reduced and direct contact with tap water is avoided. Additional measures to prevent exposure of high-risk patients to waterborne pathogen include restricting patients from taking showers if water is contaminated with legionellae; performing supplemental treatment of water for the unit; conducting periodic monitoring/culturing of the unit water supply. Healthcare providers should not use large-volume room air humidifiers that create cold aerosols unless these are subjected to high-level disinfection daily and filled with sterile water.

Engineering controls also are an important way to address the presence of Legionella, and these include ensuring that water temperature and chlorine concentration are correct. As Joseph (2006) affirms, An important aspect of preventing contamination through the water supply involves designing the water supply system to minimize stagnation and back flow as well as provide temperature control to prevent growth of bacteria.

Joseph (2006) makes the following recommendations for controlling and eliminating infections transmitted in the hospital environment through air, surface, and water:

- Careful design and maintenance of the HVAC system including incorporation of HEPA filters reduces the threat of airborne diseases.

- Proper precautions during design and construction activities are also critical to preventing the spread of airborne infections.

- Single-bed rooms are strongly recommended from an infection-control perspectiveit is easier to isolate infectious pathogens and disinfect single-bed rooms than multi-bed rooms once a patient has been discharged. The threat of infections spread through contact transmission of pathogens is also reduced in single-bed rooms.

- An important aspect of reducing infections spread through surface contact involves providing environmental support for handwashingvisible, conveniently placed sinks, hand sanitizer dispensers, and alcohol handrubs.

- Regular cleaning, maintenance, and testing of water systems and point-of-use fixtures is important for preventing the spread of waterborne infections such as Legionnaires disease.

Ninomura and Bartley advise infection preventionists and environmental services professionals to consult ASHRAE Standard 170, Ventilation of Health Care Facilities, which is the source for many of ASHRAEs best practices for the healthcare environment with respect to minimizing the spread of airborne infectious contaminants. For example:

- The design requirements for the air distribution in an operating room are stipulated including the supply air diffusers, MERV 14 filters/MERV 7 pre-filters, air velocity, etc.

- Use of ducted returns is required for rooms that have pressure relationships with adjacent rooms.

- Relatively high air exchange rates in waiting areas, and with requirement that all air is exhausted outside, provide a dilution ventilation strategy that controls the propagation of infectious agents from undiagnosed patients with airborne infectious disease.

Ninomura and Bartley say that infection preventionists can become more knowledgeable about engineering issues by attending an ASHRAE professional development course, as well as consulting chapter 6 in the 2010 Facility Guideline Institutes Guideline for Design and Construction of Healthcare Facilities. The FGI guidelines have long called for an infection control risk assessment (ICRA) which is carried out by a multidisciplinary panel of engineers, infection control professionals, architects, facility managers, etc. and is spelled out in detail in the guidelines. The ICRA is also enforced by the Joint Commission. Educational efforts have been underway for some time by professional organizations such as the American Society for Healthcare Engineering (ASHE) and the Association for Professionals in Infection Control and Epidemiology (APIC) on how to implement the ICRA; they now include the best practices from ASHRAE Standard 170. There are other opportunities for these personnel to communicate directly with the ASHRAE Standard 170 committee. The regular committee meetings, held in January and June, are open to the public and attendance by infection preventionists is welcome. Ninomura and Bartley add that infection preventionists may voluteer to serve on the Standard 170 committee. For more information, visit


Joseph A. Impact of the Environment on Infections in Healthcare Facilities. The Center for Health Design. July 2006.

Sehulster L and Chinn R. Guideline for Environmental Infection Control in Healthcare Facilities. Centers for Disease Control and Prevention (CDC)s MMWR. June 2003.

Ulrich R, Quan X, Zimring C and Joseph A. The Role of the Physical Environment in the Hospital of the 21st Century: A Once-in-a-Lifetime Opportunity. Report to the Center for Health Design for the Designing the 21st Century Hospital Project. September 2004.


Industry Experts Offer Advice on Air/Water Infection Prevention

In an era of increased airborne contamination, ICT asked members of industry to share what they believe are some of the best practices relating to containment and prevention in the healthcare environment.

Airborne Infections

Allan Schultz, Bio-Medical Devices International: The design and engineering controls that are part of all good infection prevention planning are the best methods to prevent and contain all types of infectious contamination. However, in the practical world, infections happen and spread. As evidenced by the recent NIOSH funded paper out of the University of West Virginia, we continually see evidence that aerosol transmission of harmful viruses and bacteria is likely more prevalent than less. Until there is consensus definition of the quantity of viruses/bacteria that causes infection, more personal protection is better than less. Increased use of higher protection devices, such as powered air purifying respirators (PAPRs) versus N95s and surgical masks, should be increasingly investigated on their merits of greater protection and increased user comfort and convenience. PAPRs provide inherently greater protection over mask respirators when they are worn. Additionally (and arguably more importantly), they are more comfortable with fewer wear-related side effects, and therefore enhance use-compliance, rather than decrease it as with N95s. By eliminating the need for annual fit-testing and with a designed-in universal fit, PAPRs provide greater protection without the stringent concerns for N95s as to how they are donned, use after use. Their protection is therefore less subjective. Newer designed PAPRs are increasingly more cost effective and reusable than masks, another key factor in the event of a pandemic.

Troy M. Tillman, senior global marketing manager, TSI Incorporated: One of the simplest ways to contain and prevent airborne contamination is to control the direction of air flow. This means controlling the room pressure in specialized rooms like airborne infection isolation rooms (AIIR) and protective environment (PE) rooms. AII rooms are negatively pressurized relative to the corridor, whereas PE rooms are positively pressurized. Negative pressure in AIIRs is created by exhausting more air through the rooms ventilation ducts than enters the room through the supply duct. The remaining air enters through leaks, primarily the crack under the door to the room. This air is driven by the negative pressure created from the ventilation system. The negative pressure ensures airborne droplet nuclei, like that found with tuberculosis, SARS, H1N1 and other airborne pathogens are isolated inside the room, so they do not infect healthcare staff, visitors or other patients. Typically, these isolation rooms are equipped with continuous monitoring devices designed to accurately measure low room pressures and provide alarms if and when pressure is lost. In addition, modern isolation room monitors connect seamlessly to building automation systems (BAS), to provide instant alerts and to record room conditions. By continuously monitoring these rooms, healthcare facilities not only validate safe isolation rooms, they also are able to document the room conditions for their records. PE rooms work similarly, with the airflow designed to exit the room. These rooms are designed to keep high risk immune-compromised patients from human and environmental pathogens. In other words, these rooms keep airborne pathogens out, thus protecting the patient. Many operating rooms are also maintained at a positive pressure relative to the hallway. Today, most North American hospitals dedicate a significant number of rooms to be utilized at AIIRs or PE rooms as needed, with continuous isolation room pressure monitors, to help prevent airborne contamination. Furthermore, hospitals continue to increase the number of rooms that can quickly be converted to AII or PE rooms in the event of a pandemic outbreak. In controlling airborne contamination, healthcare facilities and engineers understand the importance of controlling air flow and room pressurization.

Waterborne Infections 

Keith S. Kaye, MD, MPH, professor of medicine and director of infection prevention, epidemiology and antimicrobial stewardship, Detroit Medical Center and Wayne State University: At least 29 published studies incriminate the hospital water system as the source of serious waterborne hospital-acquired infection.1 One practice that routinely puts patients in direct contact with waterborne pathogens is the traditional basin bath. Basins and hospital tap water are used for bathing, incontinence cleanup, etc, and they pose a potential patient safety risk. There is new clinical proof that the bath basin puts patients at risk of infection. Studies show that the basin can be a source of bacteria. A study featured at APIC 2010 shows a link between the basin and catheter-associated urinary tract infections (CAUTIs). When one facility noted an increase in CAUTIs, they eliminated the basin and instituted prepackaged bathing along with other protocols. Within a month, the incidence of CAUTI was reduced to zero and stayed at zero for five months.2 Other studies also prove that basins are contaminated -- a study that tested basins at different facilities nationwide found that 98 percent of basins were contaminated with bacteria, including MRSA and VRE;3 and one facility discontinued prepackaged bathing and returned to basins as a perceived cost savings. It saw 23 additional UTIs, 151 additional hospital days and a cost of $107,741.4 Despite known risks, hospitals are still using basins. At a survey conducted at APIC 2010, 86 percent of infection control professionals said they recognize bath basins are a potential patient safety risk. 81 percent of those surveyed said they are aware that UTI-causing pathogens can originate from bath basins. However, 68 percent said their facilities still use them. Remove the basin, and eliminate a proven patient safety threat. For more information on the risks of basin bathing, visit

1. Anaissie EJ, Penzak SR and Dignani C. Arch Intern Med. 8 July 2002;163(13):1483-92.

2. Stone S, et al. Removal of bath basins to reduce catheter-associated urinary tract infections. Poster presented at APIC 2010, July 2010. 

3. Johnson D, Lineweaver , Maze L, Patients bath basins as potential sources of infection: a multicenter sampling study. AJCC, Vol 18, No 1, January 2009.   

4. McGuckin M and Shubin A. Interventional patient hygiene (IPH): case study at the bedside. University of Pennsylvania, Dept of Medicine and Rehab. Presented at American Prof Wound Care Assoc National Conf, April 2007.

David Anderson, product manager, Apollo Bath: During the almost 15 years I have been selling bathing systems, one of the most prevalent issues I am asked about revolves around infection control. While the industry has almost exclusively focused on cross-contamination and how one bathing system or another can best deal with it, the issue of self-contamination has been pretty much ignored except for those of us at Apollo Corporation. Waterborne pathogens can originate in a number of areas. Bacteria such as Legionella can come from a facilitys water source. In regard to equipment such as bathing systems, waterborne pathogens may stem from improper disinfection of equipment or the actual failure to clean and disinfect at all. Additionally, harmful pathogens such as staph, strep and E. coli can actually originate from a persons body. As a person bathes, bacteria on the body wash off, become waterborne and pose a threat to the bather, especially those who are immunocompromised or have open areas. We offer an ultraviolet light water purification system that addresses these water-borne pathogens during the bath, when the risk of exposure is at its greatest. Our UV system, called the Remedy ultraviolet water purification system, recirculates contaminated water through two ultraviolet light chambers that kill the bacterias DNA so they cannot replicate and cause infections. Nursing home populations bathed in systems equipped with our Remedy system have reported up to 50 percent reductions in urinary tract infections and 35 percent reductions in respiratory infections versus populations bathed in other brands. Clearly, ultraviolet light is a viable means of dealing with waterborne pathogens. Ultraviolet light has been used commercially for more than 100 years to purify drinking water and water used for beverage processing. Additionally, UV is routinely used to treat waste water, pond water and aquarium water. Its effectiveness cannot be denied. Facilities dedicated to eradicating waterborne pathogens obviously need to follow proper equipment cleaning and disinfection protocol, but bathing systems equipped with UV technology can help minimize the risk of these bacteria during the bath. Additionally, UV-equipped water purification systems hooked up to a facilitys source water can help minimize the chances of pathogens such as Legionella from entering the water source in the first place. In short, germicidal ultraviolet light technology can play an integral part of a facilitys overall infection control protocol.