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Impact of Indoor Air Quality (IAQ) on Patient Infections in Healthcare Environments

Senior patient being helped by healthcare staff in hospital room

Studies reveal IAQ management is needed (not just surface disinfection) to reduce healthcare-associated infections and improve patient outcomes in healthcare settings.

When humans created shelters thousands of years ago to seek refuge from harsh environmental conditions, they could not have known that a multitude of bacterial, viral, and fungal microorganisms would be cohabitants. We now know that each of us hosts dynamic ecosystems of microbes, our microbiome, that live on and in our bodies. Most of these help us survive by training our immune system, aiding our digestion, and participating in many other essential functions. Unfortunately not all microbes are beneficial, as we have recently experienced with SARS-CoV-2. Our microbiome is shed into the spaces we occupy, where the microorganisms adapt to the indoor conditions created by building materials and IAQ. Unfortunately, conditions in many modern and tightly sealed buildings promote the survival and spread of infectious rather than beneficial microbes.

The Relationship Between Sealed Buildings and Infectious Diseases

History shows a clear relationship between the modernization of buildings and the rise of certain infectious and inflammatory diseases. From 1350 - 1850 AD, when European homes became more airtight, there was an explosive increase in the number of deaths from airborne pathogens such as tuberculosis and the pneumonic strain of the Plague.

This is not just a problem of the past. The energy efficiency concerns that have dominated the last decade or more of building engineering, and the consequent tightening of building envelopes, has had a profound impact on IAQ. From these changes and the prevention of indoor air infiltration emerged “sick building syndrome” - an acknowledgement that the indoor environment does have an important role to play in occupant health.

Managing IAQ to Support Vulnerable Populations in Healthcare

Hospitals face an additional challenge in controlling infections because the primary occupants, sick or injured patients, often have impaired immunity due to illness and simultaneously may be exposed to pathogens residing in the indoor environment or emitted by other patients or sick staff. Surgical procedures, cancer treatment, and other medical interventions can breach protective skin and mucosa barriers and temporarily blunt immune responses. To make matters worse, hospital indoor environments are often populated by highly virulent and medication resistant microorganisms. We now know that antibiotic resistant genes can spread over long distances on airborne particles, increasing the spread of Antibiotic Resistant bacteria. The statement from the U.S. Surgeon General in 1967, “We have won the war on bacteria with the development of synthetic antibiotics,” has turned out to be highly inaccurate. Now is the time to, “Above All, Cause No Harm,” to patients by improper management of IAQ.

Health-Associated Infections (HAIs) and Indoor Air Quality (IAQ): Healthcare Facility Managers’ Growing Role in IAQ Management

Studies have found that at least 7% of all inpatients develop an HAI!

Understanding the “Cycle of Infection”

Patients, residents, visitors, and staff all introduce a multitude of microorganisms into healthcare and senior community environments. A single sneeze generates as many as 40,000 infectious droplets (source). Add that to other everyday patient activities such as talking, coughing, vomiting, skin shedding, and toilet-flushing, and it is easy to understand why the indoor microbial load is significant. Research has shown that it takes approximately 30 minutes before a patient or resident’s microbial footprint is established in their room, creating reservoirs of both good and pathogens which can contribute to infections in the next person or visitor entering that space.

Microbiologists now conclude that at least one-third of all HAIs involve movement of the infectious organism through the air at some point between the initial source, the environmental reservoir, and the secondary susceptible patient (See Fig.1). The significance of infection transmission through the air is becoming clearer as microbe detection assays are becoming more precise, now detecting the actual genetic material of micro-organisms rather than simply their ability to grow in petri dishes.

Fig 1: Indoor Environment and the Cycle of Infection in Hospitals The spread of infection is fueled by: 1) Significant pathogen source traffic, 2) Volatile reservoir of pathogens that are influenced by indoor environmental variables (e.g. Indoor air contaminants, human density, medical activity, building materials and cleaning products, building design/operation, outdoor air, etc), and 3) Vulnerable patients/ secondary hosts, infection in which increases pathogen transmission to fuel the cycle anew.

The cycle of infection in hospital environments puts already vulnerable patients at a higher risk of poor outcomes. Transmission between each of the components can be reduced by proper IAQ management. Good IAQ minimizes the time and distance of spread of infectious aerosols emitted by sick occupants, supports the secondary host’s immune system, and reduces the number and infectivity of pathogens in the air.

Despite the knowledge that infectious aerosols can be transmitted through the air, infection control efforts continue to focus on interrupting direct and indirect contact transmission through surface and hand hygiene protocols. While these interventions are very important, they cannot prevent the transmission of infectious airborne particles.

Emerging IAQ Strategies in Healthcare To Protect the Most Vulnerable

Historically, two basic strategies are used in ventilation guidelines for infection control: dilution of airborne pathogens, and the control of movement of airborne pathogens from one space to another. These IAQ regulations are derived primarily from demonstrations of particulate clearance and thermal comfort rather than from scientific data related to patient infections.

It is now time for stakeholders to reexamine current IAQ and ventilation standards designed primarily for comfort, and to develop more advanced health standards to protect the most vulnerable occupants, starting with hospitals, healthcare and senior communities, but to include all indoor environments.

Midrange Relative Humidity (RH) for Infection Control: 40 to 60

Another traditional component of indoor air quality management is control of humidity levels. Indoor RH management rules of thumb often embody the assumption that “less is better” — i.e. that decreased RH yields increased safety, worker comfort, and productivity.

In 2014, I participated in game-changing research on IAQ and inpatient HAIs. The results of this research were startling, clearly revealing that low RH was correlated with high infection rates and that midrange RH between 40% to 60% was correlated with significantly fewer infections. This study not only transformed my understanding of how powerful the air environment is on human health, it also inspired the development of our patented Building4Health technology. Read more about the research project that revealed the protective effects of IAQ, specifically midrange RH, on patient health.

Scientific studies have supported the conclusion that, “Through proper control and improvement of IAQ, as well as disinfection of spaces and sterilization of medical instruments, hospital infections can be significantly reduced" [source]. Surface disinfection and hand hygiene are not enough. IAQ must be monitored and managed to prevent the transmission of pathogens through the air in hospitals, other healthcare facilities, senior communities and other places where occupants are most at risk.

Key Emerging IAQ Strategies to Control HAIs:

  • Invest in medically-based IAQ platforms to measure, analyse, and manage buildings for optimal patient outcomes

  • Control RH from 40% to 60% as part of total IAQ measurement and management to reduce the risk of infection

  • Establish clear IAQ goals linked to Key Performance Indicators that include occupant health

  • Educate stakeholders about the relationship between IAQ and health, including the Facility Management team

  • Develop an ongoing communication strategy to the internal organization, occupants, and the public to educate and communicate strategies, findings, and benefits

Building4Health: A Transformative Medically-based IAQ Technology and Management System

Building4Health (B4H) addresses a significant gap in public health through creation of a medically-based IAQ index and comprehensive platform that places occupant health at the epicenter.

B4H's advanced patented algorithm, developed by a physician, is grounded in more than 20+ years of clinical work and infection control research, and is designed to optimize indoor conditions for human health while maintaining building efficiency.

As energy conservation and decarbonization pressures continue with consequent tightening of building envelopes, stakeholders must invest in robust medically-based IAQ solutions to support their most valuable assets – occupants. We believe at Building4Health that we have the tools, technology, and expertise to help you make it happen.

Museums do it. Libraries do it.

Hospitals and healthcare facilities need to manage IAQ even better.

Learn more about our Building4Health Solution.


Note: This article was adapted from the original feature article published in Engineered Systems, entitled “Mysteries in U.S. Medicine”, October 28, 2015 by Stephanie Taylor, MD.


  1. “Is Low Indoor Humidity A Driver For Healthcare-Associated Infections”, International Society of Indoor Air Quality and Climate,, July 2016, Stephanie Taylor, MD, M Arch, CIC, FRSPH(UK), CABE1*, Walter Hugentobler, MD.

  2. Buffoli M., Capolongo S., Bottero M., Cavagliato E., Speranza S., Volpatti L. Sustainable healthcare: how to assess and improve healthcare structures’ sustainability. Annali Di Igiene. 2013;25(5):411–418. doi: 10.7416/ai.2013.1942. [PubMed] [CrossRef] [Google Scholar]

  3. Ibrahim F, Samsudin EZ, Ishak AR, Sathasivam J. Hospital indoor air quality and its relationships with building design, building operation, and occupant-related factors: A mini-review. Front Public Health. 2022 Nov 8;10:1067764. doi: 10.3389/fpubh.2022.1067764. PMID: 36424957; PMCID: PMC9679624.

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