Nosocomial Infections—The Invisible Nemesis

Updated on August 28, 2023

Richard Bowser P.E copyAn Engineering Perspective

By Richard Bowser P.E.

Hospitals worldwide face a common nemesis.  In the United States nosocomial infections (hospital acquired infections) affect 1.7 million people annually, are a leading cause of death reportedly killing 100,000 people, and costs an estimated $45 billion annually.

What can be done to reduce nosocomial infections?  An effective remedy is to educate the staff, and others who come into contact with the patient, of the risks. Protocols like hand washing, maintaining sterile fields, using contact precautions, and properly disinfecting spaces will go a long way in addressing the problem.  The building systems can also help.

Nosocomial infections begin as bacteria, viruses, protozoa, and fungi. These microorganisms can reproduce at a rapid rate if the environment allows.  A properly designed domestic water supply and HVAC system can help prevent such an environment.


There are numerous codes and guidelines governing hospital plumbing and mechanical system design. The International Mechanical Code (IMC) and the Facilities Guidelines Institute (FGI) Guidelines for Design and Construction of Health Care Facilities are two required codes.  The American Society of Heating Refrigeration and Air Condition (ASHRAE) and the Center for Disease Control (CDC) are two additional organizations that establish code standards. The codes and guidelines address the hospital environment by regulating the domestic water supply, air pressure relationships, air change, outside air, and filtration requirements.


Pathogens in water are found in two forms, freely suspended in the liquid and in the biofilm on the interior surface of the pipe. Disinfections are classified as either focal or systemic.

  • Focal disinfection is directed at a portion of the water system and includes:
  • Instantaneous Heating – This works by heating water to 190°F then mixing with cold water to a desired temperature.  The system requires no specialized equipment and eliminates the need for hot water storage tanks.  Unfortunately this system only treats the hot water system, has no residual protection against re-colonization, and does not reduce pathogens that already exist in the system.
  • Ultraviolet Light is effective for a localized area and needs to be used in conjunction with other treatments.  The advantage is there are no adverse effects on the water system and no chemical by-products, tastes, or odors created in the water system.  No residual protection and continuous maintenance, to keep scale from coating the UV lights, are two disadvantages.
  • Systemic disinfection is directed at the entire system and includes:
  • Copper Silver Ionization is an effective means of eradicating pathogens from a water distribution system.  This system has low operating costs and the possibility of re-colonization is minimal.  On the down side, copper silver ionization is only used with hot water recirculation systems, regular maintenance is required to remove scale from electrodes and, a high concentration of ions in the system can lead to a blackish water color.
  • Hyperchlorination raises the chlorine in the system to a high level for a short period of time or an increased level above normal sustained.  Hyperchlorination has been shown to reduce pathogens in systems; however, it comes at a price.  Chlorine is corrosive and can cause significant pipe and system damage.  Chlorine may also cause health problems.
  • Thermal Eradication (superheat and flush) raises the temperature of the system to kill pathogens.  Typically temperatures are raised to 158°F for a thirty-minute duration.  This method is ideal if a pathogen is found, it can be quickly implemented, and costs are minimal.  An increased risk of scalding and re-colonization within months are two negatives.


There are several systems available to reduce airborne and surface pathogens including:

  • Hydrogen Peroxide Mist and Ozone Mist have been found to effectively kill microorganisms; however, additional research must be conducted to determine the effectiveness of environmental disinfecting, required concentrations, and safety for human exposure.
  • Ultraviolet Light (UV) can be used for disinfecting surfaces and airstreams.  The UV light must be exposed to the pathogen at a given intensity and duration.  Effectiveness is also determined by the distance a pathogen is located from the light source, the age of the light source,  the wavelength emitted by the light, and if there is a direct line-of-sight from the light source.  UV lamps have to be replaced periodically and staff must be trained regarding over-exposure to UV light and the use of personal protection equipment.

UV light fixtures used for disinfecting surfaces are typically portable units wheeled into a room.  The units are strategically placed for maximum surface exposure of 45 minutes.  Some fixtures sense the surroundings and increase or decrease durations accordingly.  These units have been used successfully in patient rooms, between patient discharge and new arrivals, and in operating rooms between cases.  There is no residue.  There may be a concern regarding the long term effects of UV radiation on equipment and furnishings.

UV light used in air handling units have a limited pathogen exposure time: therefore, intensities have to be high to achieve adequate pathogen kill.  A careful analysis will determine correct UV intensity to achieve the level of disinfection desired. Keeping condensate pans free of pathogens, cooling coils clean, and energy and maintenance costs low, while maintaining good airflow are benefits of UV lights located in air-handling equipment.

There is no one fix.  Facilities often use a combination of treatments to battle unwanted pathogens.  Determining the appropriate system(s) requires evaluation of the existing conditions, installation area, equipment first cost, operating costs, and availability of operating staff. Systems and personnel practices will not be effective without an effective monitoring program and a staff committed to the goal.

Richard Bowser is a Professional Engineer and Senior Associate at Stantec Architecture and Engineering LLC. Ric works in the Stantec Butler, Pennsylvania Office and can be reached at [email protected].

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