HVAC Systems Prove Sufficient to Reduce Viral Pathogen Transmission Within a Hospital


Live attenuated influenza vaccine particles were released into a closed room to measure how many particles would get through the HVAC system.

When the COVID-19 pandemic hit, many hospitals struggled to find negative pressure rooms approved by the Centers for Disease Control and Prevention (CDC) for the sudden influx of COVID-19 patients. However, many hospital systems had a very limited number of negative pressure rooms (Table). One of the main considerations was the recirculation of air. If the air used is not 100% outside air, would the air being recirculated transport viral-containing particles from one patient room to the next?

A recent study, “Requirements to Reduce Viral Pathogen Transmission in Health Care HVAC Systems,”presented at the Society for Healthcare Epidemiology of America (SHEA) Spring conference, held April 12-14 in Colorado Springs, Colorado, explained that the viral-containing particles can be transported through the HVAC system even with high efficiency particulate air (HEPA) filters. The study was presented by Werner Bischoff, MD, MS, PHD, MS, the medical director of infection prevention and health system epidemiology at the Atrium Health Wake Forest Baptist Hospital System and a professor at Wake Forest School of Medicine.

Negative Pressure

Table 1: Negative Pressure Room (Adobe Stock)

“CDC sets [a limited] risk of transmission of pathogens that are emitted from one patient inside a patient room that is then transferred through a heating, ventilation, and air conditioning (HVAC) system back to maybe an adjacent patient room or an entire unit,” Bishoff told Infection Control Today® (ICT®) in an exclusive interview. “What you don't want is to have a ton of transmissions and in a very closed-up area through the HVAC system.”

For the first time, this study demonstrates that “viral containing particles can be transported via a hospital HVAC system from one patient room to the next,” Bishoff wrote in the study. “Taking into account the loss of virus within the HVAC system, the combination of MERV8+MERV16 filters reduces the virus burden reaching an adjacent room to levels well below the human infectious dosages for influenza and other highly infective viruses. Our findings indicate that MERV8+MERV16 filters provide protection against virus transmission through HVAC systems and are a cost-conscious alternative to HEPA filters.”

Considering future investigations, Bishoff said to ICT®,“I think it would be nice to look at the more novel technologies that are coming out [like] neurons that are highly promoted, especially by industry—that is ionization…Mechanical ventilation isn't established [with] these newer technologies, We need a lot more data to say that [air filtration systems] are really safe and do what they promised to do.” Previously, ICT® has reported on this topic here, here, and here.

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