Anticipating Future Needs in Airborne Infection Control in Healthcare Facilities

Patrick Chambers. Australian Building Services Discipline Leader, Stantec

Hospitals and healthcare facilities hold a paradoxical role in society: they are intended to be places of healing, yet they also carry inherent risks as environments where diseases can propagate. This duality has long been recognized, with some of the most significant breakthroughs in germ theory emerging from observations of disease transmission in healthcare settings (e.g., Ignaz Semmelweis). Florence Nightingale captured this contradiction poignantly in Notes on Hospitals (1859), stating that “the very first requirement in a hospital is that it should do the sick no harm.” Yet, in the wake of the COVID-19 pandemic, the question remains: are we adequately positioned to fulfill this promise?

The pandemic brought airborne infection transmission—and the critical role of indoor air quality (IAQ)—to the forefront of global discourse. It highlighted numerous examples of nosocomial healthcare-associated infections (HAIs), raising awareness of how respiratory aerosols serve as a dominant mode of disease transmission. Poor indoor air quality can significantly exacerbate these risks, yet for much of the pandemic, clarity was lacking regarding the specific aspects of IAQ that should be prioritized and the best engineering solutions to mitigate airborne transmission. This uncertainty underscores the need for a robust framework to address airborne infection risks in healthcare facilities.

A pivotal development in this area has been the publication of ASHRAE 241: Control of Infectious Aerosols (2023). Emerging from discussions between ASHRAE and the White House COVID-19 Response Team, this standard represents a significant step forward in defining actionable benchmarks for airborne pathogen control. Unlike traditional IAQ standards, ASHRAE 241 focuses explicitly on minimizing the risk of infectious aerosol transmission, introducing the concept of Equivalent Clean Airflow (ECAi) as a quantitative metric for measuring and achieving safer indoor environments. It offers a groundbreaking approach by allowing flexibility in how clean air is delivered—whether through ventilation, filtration, or advanced air-cleaning technologies—thus broadening the toolkit available to engineers and facility managers.

Key Challenges in Airborne Infection Control

The mechanics of airborne infection transmission are complex and multifaceted. Infection occurs when a sufficient quantity of viable infectious aerosols are inhaled by a susceptible individual, a process influenced by variables such as ventilation rates, air change effectiveness, and localized airflow patterns. However, accurately quantifying and mitigating this risk across different indoor environments is a significant challenge.

Since the onset of the pandemic, a proliferation of academic studies, guidance documents, and industry standards has sought to address this complexity. Institutions like the CDC, WHO, and ASHRAE have issued recommendations to guide HVAC professionals in implementing effective controls. Yet, questions persist: Are current ventilation performance metrics sufficient to minimize nosocomial infections? What does “good” look like in terms of airborne infection control? And how can emerging technologies be integrated into existing systems to enhance safety?

Engineering Controls: A Layered Approach

Effective airborne infection control requires a layered approach that combines multiple engineering controls to reduce the concentration of infectious aerosols in the breathing zones of occupants. These controls include:

1. Ventilation Rates: Increasing the supply of fresh air is a foundational strategy for reducing aerosol concentrations. However, research (e.g., Mikszewski et al., 2021) suggests that ventilation alone may be insufficient for highly contagious diseases such as tuberculosis or measles, highlighting the need for complementary controls.

2. Filtration Efficiency: Conventional filters (particularly high-efficiency particulate arrestors (HEPA) filter units) are well-established tools for removing airborne particles, including infectious aerosols. ASHRAE 241 emphasizes the importance of filtration as a cost-effective and scalable solution, particularly in recirculated air systems.

3. Advanced Air-Cleaning Technologies: Innovations such as UV-C germicidal irradiation, ionization, and catalytic air cleaning are gaining traction as viable alternatives or supplements to traditional ventilation and filtration. These technologies are particularly valuable in scenarios where increasing ventilation rates is impractical due to energy or infrastructure constraints.

4. Air Change Effectiveness: The effectiveness of ventilation systems in delivering clean air to occupied spaces depends on factors such as diffuser placement, airflow patterns, and room geometry. ASHRAE 241 introduces methodologies for assessing and optimizing air change effectiveness, which is critical for ensuring the removal of aerosols from the breathing zone.

5. Environmental Controls: Temperature and humidity levels play an indirect but important role in airborne infection control. Maintaining optimal conditions can inhibit pathogen viability and reduce the risk of secondary issues like mold growth.

ASHRAE 241: A Game-Changer for Airborne Infection Control

The release of ASHRAE 241 has been heralded as a watershed moment for the HVAC industry’s response to infectious aerosol transmission. By introducing the concept of Equivalent Clean Airflow, the standard shifts the focus from traditional ventilation metrics to a more holistic and flexible framework. For example, it allows for the integration of increased outside air, portable air purifiers, in-duct filtration systems, and UV-C technologies to achieve the recommended ECAi levels for specific spaces.

This flexibility is particularly important in resource-constrained settings where increasing ventilation rates may not be feasible. For instance, a healthcare facility could meet ECAi requirements by combining outdoor air ventilation with recirculated air treated through HEPA filtration and localized air purifiers. Such strategies not only improve safety but also offer cost-effective and energy-efficient solutions.

However, ASHRAE 241 also acknowledges its limitations. The standard primarily addresses long-range aerosol transmission and assumes uniform air mixing within spaces. It does not fully account for short-range transmission scenarios, where localized airflow patterns can significantly influence infection risks. Addressing these gaps will require further research and refinement of the standard in future iterations.

Looking Ahead: Anticipating Future Needs

The COVID-19 pandemic has fundamentally reshaped public expectations for indoor air quality, particularly in healthcare settings. Patients, staff, and visitors now demand safer environments, and the momentum for higher IAQ standards is unlikely to wane. This societal shift underscores the need for continued innovation in airborne infection control technologies and methodologies.

As we look to the future, the HVAC industry must focus on developing scalable, cost-effective solutions that balance safety, energy efficiency, and sustainability. Initiatives like the Safe Air Project, which frames IAQ as a safety and inclusion issue, highlight the broader implications of this work. By ensuring equitable access to clean indoor air, we can uphold Florence Nightingale’s principle that places of healing should “do the sick no harm” and extend this promise to all indoor environments.

The path forward will require collaboration across disciplines—engineering, public health, and policy—to ensure that the lessons of the pandemic translate into lasting improvements. With tools like ASHRAE 241 providing a robust foundation, the industry is well-positioned to anticipate and meet the challenges of airborne infection control in the decades to come.

Patrick holds a Bachelor of Mechanical Engineering from the University of Queensland and a Master of Science in Sustainable Urban Development from Oxford University. He is a Chartered RPEQ Engineer with 15 years consulting engineering experience in various sectors and multidisciplinary teams.

Pat is the Australian Building Services Discipline Leader at Stantec and is actively involved in a number of industry bodies and research programs surrounding the topic of indoor air quality. Further, the focus of his consulting experience is within the healthcare sector and he is a regular contributor to industry publications and conferences within the Australian healthcare sector.

Connect with Patrick

Hear Patrick speak further on this topic at the upcoming IHEA National Conference.

His presentation is titled ‘Anticipating Future Needs in Airborne Infection Control Within Healthcare Facilities’.

Patrick will speak at 2:50 PM on Tuesday 27th, Day Two of the Conference in Sydney.

Register Here