Industry Voices—The case for hospitals to invest in cleaner air

Back in the 1800s, all assumed infectious diseases were spread by foul air or “miasma,” often arising from sewage.

In 1854, a severe cholera outbreak occurred in London and was investigated by John Snow, M.D., the father of modern-day epidemiology. He concluded that the outbreak was spread not by the air but by surfaces and identified the culprit as a water pump handle on Broad Street. Since then, healthcare has progressively discounted airborne spread as a significant component in many outbreaks. However, a paradigm shift is needed to refocus our efforts on aerosolization of dangerous pathogens.

Although there has been abundant attention on the importance of masking in healthcare settings to prevent the transmission of airborne pathogens, there are also detractors who are quick to point out that many studies regarding masking have failed to demonstrate a significant effect. There are two reasons for this.

First, many of the research protocols did not use masks that were designed to stop airborne pathogens. Second, when surgical masks and N95 respirators were used, they were used inconsistently. Only one break in protocol can cause the front-line worker to become infected.

Patients with active infections from SARS-CoV-2, influenza or other airborne pathogens are not consistently placed in negative pressure rooms. Thus, there is a significant potential for these pathogens to travel throughout a facility, necessitating continuous masking. Similar to hand-washing, continuous masking is almost impossible to achieve. Breaks will be taken for eating and drinking, and some may choose to discontinue wearing masks to relieve discomfort. Masks should be viewed as a layer of protection and in themselves not adequate to maintain a healthy workforce.

A second layer of protection, that of clean air, is needed in all facilities. There are two goals: One is to remove airborne pathogens and the other is to maintain a low level of carbon dioxide. In healthcare settings, even the common cold can be deadly to immunocompromised patients. Carbon dioxide levels can be measured as a surrogate for clean air. As carbon dioxide increases in a building, the risk of airborne pathogens increases, as does impairment of cognitive function of those inside. Outdoor air has a carbon dioxide level of 400 ppm.

The American Society of Heating, Refrigeration, and Air-conditioning Engineers (ASHRAE) recommends an indoor CO2 level of 870 ppm or below. To achieve this, a minimum ventilation rate of 10 liters per second per person is needed. Lowering CO2 improves cognition: Higher CO2 levels can also cause drowsiness and affect concentration. Joseph Allen, et al., have demonstrated that compared to CO2 levels of 550 ppm, cognitive function was 15% lower at a level of 945 ppm and 50% lower at a level of 1400 ppm. For “strategy” (the ability to plan, sequence and prioritize actions) these scores were 16% and 78% lower, respectively. “On average, a 400 ppm increase in CO2 was associated with a 21% decrease in a typical participant’s cognitive scores across all domains …”

Lowering CO2 levels also decreases the spread of infections: Research in classroom settings has shown that air exchanges greater than 10 liters per second per person are associated with an 80% decrease in the risk of infection. Just in the last few days, the Centers for Disease Control and Prevention released recommendations that indoor venues have a minimum of five complete air exchanges per hour. For emergency rooms and radiological waiting areas, ASHRAE has recommended at least 12 complete air exchanges per hour.

New draft ASHRAE recommendations released in May 2023 address “Control of Infectious Aerosols.” Equivalent outdoor airflow in healthcare waiting rooms should be 60 liters per second per person (L/s/p), 45 L/s/p in common treatment areas and 90 L/s/p in healthcare patient rooms.

The White House Office of Science and Technology has stressed the importance of clean air in stopping the spread of airborne disease, not only with clean outside air but by the incorporation of other modalities including HEPA filtration and UV-C lighting. Research has found that for each 100 ppm increase in CO2 the chances of detecting an airborne pathogen increase by 9%.

ASHRAE Recommendations

A MERV 15 HEPA filter removes approximately 85% of airborne pathogens. As the air recirculates, it is progressively cleaned. A major disadvantage of MERV filters is that they increase resistance to airflow and place increased stress on a facility’s air filtration system. This has led some facilities to focus on UV-C germicidal lighting. Ultraviolet Germicidal Irradiation (UVGI) is a cost-effective, time-tested solution that has been used for over 70 years. In the 1950s, UVGI was used for controlling the spread of tuberculosis. A central UVGI HVAC system is not as effective as upper-room UV-C devices. Upper-room devices cost between $1500 to $2500 and will kill bacteria, virus and fungi soon after they are aerosolized. The “C” wavelength is shorter than UV-A and UV-B and is less penetrating, thus posing less of a risk to humans. In addition, the upper room fixtures prevent direct exposure to ultraviolet light. Upper room UV-C fixtures are ideal for crowded indoor venues such as waiting rooms, break areas and lobbies.

Clean air is dependent upon room occupancy. UV-C devices can provide a large increase in equivalent complete air exchanges that are needed when room occupancy surges. It needs to be noted that these devices will not lower or impact CO2 levels.

One may ask, who will be measuring CO2 levels in my facility? The answer is patients and families. Portable CO2 monitors can be purchased on Amazon for under $150. They are becoming increasingly popular as more attention is being focused on clean air. Many healthcare facilities and the public are undergoing a paradigm shift in how they approach airborne spread of disease. I try to frequent venues which have CO2 levels of 700 ppm or lower. It is not unreasonable for healthcare facilities to set this as their goal, along with meeting the proposed ASHRAE recommendations.

Compared to the purchasing of N95 masks, the economic investment in clean air is much lower and should easily be offset by the advantages of maintaining a healthy workforce and increasing the safety of healthcare provided to patients.

Kevin Kavanagh, M.D., is founder and president of the patient advocacy group Health Watch USA.