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Air Filtration: A Prescription for Healthier Hospitals and Patients

Air Filtration: A Prescription for Healthier Hospitals & Patients Photo

By: Robert Martin, CAFS, Associate Category Manager, Kimberly-Clark Professional Filtration  |   01.16.15

Hospitals and other healthcare facilities face increasing pressure to reduce healthcare-acquired infections (HAIs). Improving patient outcomes and avoiding un-reimbursable costs are just two reasons healthcare facility managers need to pay special attention to airborne HAIs and how to stop them. 

One strategy lies within the facility’s HVAC system, which can help to eliminate or significantly reduce airborne respiratory illness triggers that occur within a building, such as microorganisms, dust and allergens. Effective air filtration is the crucial HVAC system component that can reduce these triggers and thus help to reduce airborne infectious disease transmission. 

The Air Inside

Poor indoor air quality (IAQ) may cause outbreaks of sick hospital syndrome (SHS), causing headaches, fatigue, eye and skin irritations and other symptoms. There are a number of infectious agents linked to airborne transmission in healthcare facilities including Aspergillus (contaminated air ventilation systems have been associated with outbreaks of nosocomial aspergillosis), Mycobacterium tuberculosis, Bacillus spp, VZV, measles virus (i.e., rubeola), Legionella bacteria, methicillin-resistant Staphylococcus aureus, and smallpox virus (i.e. variola major). 

How and why do airborne HAIs spread? A number of factors may contribute. The increasing age of hospitals and other healthcare facilities is generating an ongoing need for repair and remediation work that can introduce or increase contamination of the air in patient-care environments. For example, site renovation and construction can disturb Aspergillus-contaminated dust and produce bursts of airborne fungal spores, which have been associated with clusters of HAIs in immunocompromised patients. 

Decreased performance of healthcare facility HVAC systems, filter inefficiencies, improper installation and poor maintenance practices can also contribute to the spread of airborne HAIs. For example, gaps in and around filter banks and heavy soil and debris upstream of poorly maintained filters have been implicated in healthcare-associated outbreaks of aspergillosis. Additional pathogens that may be found in air filters in healthcare settings include Mucorales (Rhizopus spp), Penicillium spp, Acremonium spp and Cladosporium spp. 

Removing Dangerous Particles from the Air

Most of the respirable dust and particles people breathe into their lungs is approximately 7 microns or smaller – a fraction of the size of a grain of sand. The smallest, most toxic particles (2.5 microns in diameter or less) are most likely to travel to the deepest part of the lungs, where they can cause a variety of respiratory and other health problems. But it’s really the submicron-sized particles that are of most concern; airborne bacteria can be as small as 0.3 microns. 

To determine a filter’s efficiency in removing dangerous submicron particles, it is important to look beyond the filter’s Minimum Efficiency Reporting Value (MERV). Evaluation of the full ASHRAE 52.2 test report (specifically the Fractional Particle Size vs. Particle Diameter Curve) will provide the efficiency of the filter over three particle size ranges: E1 (very fine particles in the 0.3 to 1.0 micron range), E2 (fine particles in the 1.0 to 3.0 micron range), and E2 (coarse particles in the 3.0 to 10.0 micron range). High E1 and E2 efficiencies are critical for providing for good IAQ and helping patients, staff and visitors avoid illness due to poor IAQ. 

Be aware that many pleated filters today (especially at commonly used MERV 8) have very low E1 and E2 efficiencies. In fact, under the ASHRAE 52.2 Standard, there is no minimum requirement for E1 particulate capture below a MERV 14 and no minimum requirement for E2 particle capture below a MERV 9. It is therefore possible to have a MERV 8 filter with better E1 particle capture than a MERV 11 filter, depending on the filter media used. 

A Balanced Approach to Air Filtration

When selecting filters, consider those with filter media that has a good balance of mechanical efficiency and electret efficiency (via an electrostatic charge), so you get high initial and high sustained filtration efficiency over the filter’s lifecycle. 

The electrostatic effects created in an electret-charged media are particularly useful increasing the capture of submicron particles, thus filters with electret-charged media often provide better E1 and E2 performance than is required by their MERV rating. In addition, recent testing showed MERV 8 filters using electret-charged media performing on average 20 percentage points higher in E1 and E2 efficiency than mechanical filters on the market today. 

In addition, electret-charged filters almost always deliver lower airflow resistance in the same filter construction as mechanical-only filters, which translates into reduced energy costs. 

Not all electret-treated media filters are the same. It’s best to look for a filter that has a depth-loading media with a gradient density structure in which the media’s fibers are more loosely packed on the upstream side and more densely packed on the downstream side. This structure helps to reduce airflow resistance, enhance dust loading and prevent face loading of the filter. 


HAIs can be expensive, for both patients and hospitals. Careful consideration of a filter’s efficiency – especially for the removal of dangerous submicron particles – may help healthcare facility managers make a more informed purchase decision toward the goal of improved IAQ and reduced HAIs.



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