The Role Of 3-Dimensional (3-D) Cleaning in Health Care

Realism is what 3-D glasses aim to give theatergoers through polarized lenses, digital projectors, and IMAX 3-D camera systems for an immersive experience that imitates real life.

A 3-D approach to environmental cleaning aims to give Infection prevention and control (IPC) and environmental services (EVS) a realistic view of indoor spaces that includes not only surfaces (2-D) but the air above surfaces (3-D) because a) we often deal with immune-compromised persons; b) infectious exposure can occur through both airborne and surface routes, and c) infectious exposure is most often a 3-dimensional and immersive rather than a 2-dimensional process.
Respiratory infections are a major part of health care-associated infections (HAIs), as between 23 to 63% of all HAIs are respiratory infections.^1-3

“If the pathogen has some part of its life cycle in the respiratory tract, it is more likely to be present in aerosols generated and projected into the surrounding air by breathing, talking, coughing, sneezing and singing,” notes researchers in the 2006 report, “Factors involved in the aerosol transmission of infection and control of ventilation in health care premises.”⁴

In 2024, the World Health Organization suggested the umbrella term infectious respiratory particles (IRPs) to simplify and include aerosols (tiny particles), droplets (larger particles), and other airborne infectious particles in a single metric.⁵

While our ability to assess the quality of 2-D surface cleaning using simple, science-based tools is fairly well understood (see Sidebar, “Seeing in 2-D”), seeing airborne matter such as IRPs is not; hence, this article focuses on the third dimension of cleaning—air monitoring and purification.

As the medical model teaches us, diagnosis precedes treatment, so diagnosing indoor air should precede treating or purifying it, and this involves understanding how IRPs behave indoors.

One way to visualize the movement of IRPs indoors is to use 3-D modeling. 3-D modeling can help simulate the behavior of particles in different scenarios, such as inpatient rooms, waiting areas, restrooms, or hallways. By using 3-D modeling, we see how factors such as the distance, duration, and direction of exposure; the size, shape, and density of the particles; the airflow, temperature, and humidity in the space; and ventilation and filtration of the indoor air, can potentially affect the risk of infection.

Generally, smaller and lighter particles stay suspended in the air for more extended periods than larger and heavier ones, which tend to settle on surfaces more quickly. Some studies estimate that the average time for bacteria and viruses to stay airborne is about 1 to 2 hours, though this varies widely depending on conditions and types of microbes. For example, some research has shown that the coronavirus that causes COVID-19 can remain viable as an IRP for up to 3 hours, while other studies suggest that it can persist for less than an hour. (See sidebar, “IRP Dynamics”)

In addition to 3-D modeling, active air monitoring technology enables “seeing” invisible airborne particles down to .1 micron (eg, the COVID-19 virus is ~.1 micron in size)—plus detecting Total VOCs (TVOC), carbon dioxide (CO₂), temperature, and humidity—and when coordinated with real-time air purification, enables a 3-D approach to facility cleaning.

Seeing in 2-D

One method to see how well surfaces or fomites are cleaned or wiped is to use a fluorescent targeting method. Per the CDC, fluorescent gel marking systems enable marking high-touch surfaces before cleaning, and “there are several studies demonstrating the accuracy of the system to objectively evaluate cleaning practice and quantify impacts of educational interventions on cleaning.”

The steps are 1) mark areas to be cleaned with an invisible fluorescing gel, 2) once staff completes cleaning, check areas with a fluorescent light to see missed spots, 3) use results for retraining, and 4) measure outcomes and repeat the cycle for improvement.

ATP Meters detect the presence of ATP found in organic matter (both microbial and nonmicrobial) on an object or surface. “Objects are tested before and after cleaning to determine the effectiveness of a cleaning procedure. A numeric score can be generated based on the proportion of marked surfaces/objects that were under the pre-determined threshold”⁸

The best strategy for combining indoor air quality (IAQ) monitoring and purification in health care facilities depends on the type, level, and source of the indoor environmental contaminants, as well as the specific needs and characteristics of the people in the facility. However, some general principles and guidelines are:

Continuous air monitoring is key to identifying and quantifying indoor air pollutants, helping assess health effects, and evaluating the effectiveness of air purification measures in real time. For example, units may have internal fans that actively sample the air and upload the data wirelessly to a building management system or cloud-based software every several seconds.

Continuous monitoring is important as it shows trends such as particle levels during vacuuming or cleaning processes, VOC levels during medical procedures, disinfection or other activities, and or CO2 levels, which serve as a proxy for other pollutants.

Air monitors should be accredited by an independent source such as RESET (Regenerative Ecological, Social, and Economic Targets), which specifies requirements to help ensure the quality, timeliness, and accuracy of data—such as levels of fine particles 2.5 microns (PM 2.5) and smaller, TVOCs, CO2, Temperature, and Humidity—and enables periodic calibration and audits of monitor performance. RESET is recognized by the International WELL Building Institute (IWBI) and the LEED IAQ innovation credit.

Use of In-Room or Proximity Air Purification Systems

Based on the current research and the guidelines, the following recommendations can be made for the use of in-room or proximity air purification systems in health care facilities:

• These systems should be used as a supplement, not a substitute, for the general ventilation and filtration systems in health care facilities, and they should be integrated with other infection control measures, such as personal protective equipment, hand hygiene, disinfection, and or isolation.

• These systems should be used in areas or rooms where the risk of airborne transmission of infections is high, such as the isolation rooms, the intensive care units, the emergency departments, or the operating rooms, and where the ventilation or the filtration systems are inadequate or insufficient.

• These systems should be selected based on the type and the size of the device, the technology and the efficiency of the air cleaning process, the air exchange rate and the ventilation rate in the room, the placement and the orientation of the device, the occupancy, immune-vulnerability, and activity level in the room, and the characteristics and the concentration of the airborne pathogens.

• These systems should be installed, maintained, and monitored by qualified and trained professionals. They should comply with the relevant standards, regulations, and recommendations from ASHRAE, ASHE, the CDC Guidelines for Environmental Infection Control in Health-Care Facilities, or the WHO Guidelines on Core Components of Infection Prevention and Control Programs, etc.

• These systems should be evaluated in terms of their effectiveness, safety, and cost-effectiveness, and the results should be reported and disseminated to the stakeholders, such as the patients, the health care workers, the managers, or the policymakers.

Air monitors with customizable sensors enable flexibility in detecting particular airborne contaminants and should offer data security features to control access to sensitive information.

Air purification can be achieved by various means, such as ventilation, filtration, UV-C, adsorption, and more. The choice and combination of the air purification methods should be based on the specific characteristics of the indoor air pollutants, such as their size, concentration, chemical composition, and biological activity, as well as the availability, cost, efficiency, and safety of the methods. For example, EPA states that “in order for an air cleaner to be effective in removing viruses from the air, it must be able to remove small airborne particles (in the size range of 0.1-1 um).”⁶

Air purifiers in healthcare spaces should incorporate technologies associated with log reduction, such as a 4-log (99.99%) to 6-log (99.9999%) microbial log reduction.⁷

Air monitoring and purification should be integrated and coordinated with surface cleaning protocols as part of a comprehensive, holistic, 3-D approach to indoor environmental quality management in health care facilities.

IRP Dynamics

A study by Bourouiba et al (2014) used high-speed video imaging to record the dynamics of human coughs and sneezes. They found that the expelled fluid can form a turbulent gas cloud that can carry the droplets up to 7-8 meters, much farther than the commonly assumed 1-2 meters. They also found that the droplet size distribution within the cloud is different from that at the exit of the mouth or nose, suggesting that evaporation and coalescence can affect the fate and the potential for infection of the droplets.

https://lbourouiba.mit.edu/sites/default/files/documents/14BourouibaBush-sneezecloudJFM_corrected.pdf

A study by Asadi et al (2019) used laser light scattering to measure the size and the number of droplets emitted by human speech. They found that the louder the speech, the more and larger droplets are produced and that some individuals (called superemitters) can produce an order of magnitude more droplets than others. They also found that the droplets can remain airborne for more than 10 minutes in a stagnant air environment, indicating that air currents can transport them over long distances.

https://www.nature.com/articles/s41598-021-89078-7?fromPaywallRec=false

Liu, K., Allahyari, M., Salinas, J.S. et al. Peering inside a cough or sneeze to explain enhanced airborne transmission under dry weather. Sci Rep 11, 9826 (2021). https://doi.org/10.1038/s41598-021-89078-7

A study by Dbouk and Drikakis (2020) used computational fluid dynamics to simulate the transport and evaporation of respiratory droplets in different environmental conditions. They found that factors such as humidity, temperature, and wind speed can significantly affect the droplets' travel distance and lifetime. For example, they estimated that at 50% relative humidity, a droplet of 10 microns in diameter can travel up to 6.6 meters, while at 90% relative humidity, it can travel only up to 2.4 meters.https://pubmed.ncbi.nlm.nih.gov/32574229/A study by Bourouiba et al. (2014)used high-speed video imaging to record the dynamics of human coughs and sneezes. They found that the expelled fluid can form a turbulent gas cloud that can carry the droplets up to 7-8 meters, much farther than the commonly assumed 1-2 meters. They also found that the droplet size distribution within the cloud is different from that at the exit of the mouth or nose, suggesting that evaporation and coalescence can affect the fate and the potential for infection of the droplets.

https://lbourouiba.mit.edu/sites/default/files/documents/14BourouibaBush-sneezecloudJFM_corrected.pdfViolent expiratory events: on coughing and sneezing Lydia Bourouiba1,2,†, Eline Dehandschoewercker3 and John W. M. Bush1 1Department of Mathematics, Massachusetts Institute of Technology, Cambridge, MA 02130, USA 2Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, MA 02130, USA 3PMMH- ESPCI, O207 10, rue Vauquelin, 75005 Paris, France (Received 4 January 2013; revised 29 December 2013; accepted 7 February 2014)

A study by Asadi et al. (2019) used laser light scattering to measure the size and the number of droplets emitted by human speech. They found that the louder the speech, the more and the larger droplets are produced, and that some individuals (called superemitters) can produce an order of magnitude more droplets than others. They also found that the droplets can remain airborne for more than 10 minutes in a stagnant air environment, indicating that air currents can transport them over long distances.

https://www.nature.com/articles/s41598-021-89078-7?fromPaywallRec=false

A study by Dbouk and Drikakis (2020) used computational fluid dynamics to simulate the transport and the evaporation of respiratory droplets in different environmental conditions. They found that factors such as humidity, temperature, and wind speed can significantly affect the travel distance and the lifetime of the droplets. For example, they estimated that at 50% relative humidity, a droplet of 10 microns in diameter can travel up to 6.6 meters, while at 90% relative humidity, it can travel only up to 2.4 meters.

https://pubmed.ncbi.nlm.nih.gov/32574229/

Dbouk T, Drikakis D. On coughing and airborne droplet transmission to humans. Phys Fluids (1994). 2020 May 1;32(5):053310. doi: 10.1063/5.0011960. PMID: 32574229; PMCID: PMC7239332.

These studies suggest that the travel distance of airborne droplets or aerosols is not fixed but rather depends on various physical, biological, and environmental factors.

ASHRAE 62.1’s Indoor Air Quality Procedure (IAQP) approves the use of peripheral air purifiers to meet its clean air equivalency requirements as an alternative to mandatory HVAC ventilation rates, such as 5 air changes per hour. This reduces the load placed on HVAC systems and the need to use costly high-MERV filters at the HVAC level, lowering resistance to airflow, fan/motor wear, energy, and overall costs.

ASHRAE Standard 241, Control of Infectious Aerosols, released in 2023, further validates the approach as it “establishes minimum requirements aimed at reducing the risk of disease transmission through exposure to infectious aerosols” and provides “requirements for use of filtration and air cleaning … [eg, HEPA filters, UV, etc] for equivalent clean airflow rate target per occupant of pathogen-free airflow, reducing the risk of infection.”

To effectively use ASHRAE’s IAQP in health care, facility managers should integrate it with the sometimes more stringent air-change recommendations from ASHE, facility operations, and health care-focused groups. This involves:

•Conducting thorough risk assessments to identify and control potential sources of contamination.

•Ensuring that air quality targets align with health care-specific requirements, particularly in critical areas such as operating rooms and isolation units.

•Implementing robust monitoring and maintenance programs to verify that air quality remains within acceptable limits.

In-room or peripheral units equipped with MERV 19 or ULPA filtration and other technologies, such as UV-C, can do the heavy lifting regarding particle removal closer to the source and effectively reduce airborne pathogens.

WHO has recently updated its list of dangerous pathogens that could cause the next pandemic—consulting with some 200 scientists about 1,652 pathogenic species—finding the number has jumped to 30 vs about a dozen in 2017-2018—and many of these are airborne.⁹

Conclusion
While we do not have 3-D glasses to assess our work in cleaning on and above surfaces, a 3-D approach to hygiene using surface and air monitoring and purification systems provides a solid path to realism in the health care theatre.