Review shows UV radiation in HVAC systems inactivates viruses

Aerosols can transmit respiratory viruses. For example, evidence from studies suggests that the novel severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which causes COVID-19 disease can spread via the airborne route, especially in poorly ventilated indoor environments. Heating, ventilation, and air conditioning (HVAC) systems play a significant role in minimizing airborne transmission of viruses.

Effectiveness of UV exposure in reducing viral transmission

Recently, Canadian researchers conducted a systematic review of the literature examining the effectiveness of various features of HVAC designs in reducing viral transmission and reported the results for ultraviolet (UV) radiation.

The researchers followed international standards for systematic reviews, performed a comprehensive search, and gathered findings from 32 relevant studies published between 1936 and 2020. This study is published on the medRxiv* preprint server.

Increase in UV dose

The study results showed that viruses and bacteriophages are inactivated by UV radiation. An increase in UV dose correlates with a decrease in the survival fraction of bacteriophages and viruses. Also, increased relative humidity was associated with decreased susceptibility to UV radiation.

UV dose and corresponding survival fraction were found to be affected by air changes per hour, airflow pattern, and UV device location. UV radiation was linked to decreased transmission in animal as well as human studies.

UV radiation susceptibility (Z) and relative humidity (RH) Each colour represents one study. Reported RH ranges shown as average RH values.  ∼Cutler at al33 reported that susceptibility (Z) was significantly lower at ≥80%RH (shown at 80%RH) compared with 25%-79%RH (shown at 52%RH).  *Walker and Ko10 calculated susceptibility from a single dose and corresponding survival fraction, rather than dose-response of UV dose and survival fraction.  ^Lin et al35 calculated susceptibility from a single dose and corresponding survival fraction for “fast decay” and from the dose-response of UV dose and survival fraction for “slow decay”.
UV radiation susceptibility (Z) and relative humidity (RH) Each color represents one study. Reported RH ranges shown as average RH values. ∼Cutler at al33 reported that susceptibility (Z) was significantly lower at ≥80%RH (shown at 80%RH) compared with 25%-79%RH (shown at 52%RH). *Walker and Ko10 calculated susceptibility from a single dose and corresponding survival fraction, rather than dose-response of UV dose and survival fraction. ^Lin et al35 calculated susceptibility from a single dose and corresponding survival fraction for “fast decay” and from the dose-response of UV dose and survival fraction for “slow decay”.

Practical implications

While in-duct ultraviolet germicidal irradiation (UVGI) focuses on virus transmission throughout the HVAC system of a building, upper-room UVGI addresses virus transmission in a single room in that building.

The relationship between UV dose and survival fraction of a virus determines the susceptibility of the virus, which can be affected by relative humidity.

Modeling studies have shown that practical implementation of UVGI in HVAC systems must consider airflow patterns, UV device location, and air changes per hour.

“External factors such as ventilation and relative humidity also play an important role in UV effectiveness.”

The extensive scientific evidence from this study analyzing the impact of UV radiation on virus transmission can guide the implementation of systems to mitigate airborne transmission and identify priorities for future research works. Future field studies of UVGI systems could focus on gaps in existing research and offer important insights into system performance in real-world situations.

UV inactivation

Inactivation of airborne viruses using UV is regulated by the UV dose. The required UV dose varies based on the virus type, capsid structures, and host cell repair mechanisms. For example, studies have shown that dsRNA and dsDNA viruses need two times the dose required for their single-stranded counterparts for 90% inactivation.

Other studies have found that adenovirus was more resistant to inactivation than SARS. This resistance to inactivation is due to the double-stranded nature of its DNA genome and the ability of the virus to shield from UV radiation with the help of small proteins present along with other viral particles.

“Experimental studies of UV radiation have consistently demonstrated high susceptibility of viruses (or simulant agents) with sufficient UV dose.”

Overall, this work offers a comprehensive review of existing scientific literature examining the effectiveness of UV radiation and virus transmission and survival. Information about the UV susceptibility of aerosolized SARS-CoV-2 has not yet been reported. However, some studies are examining the effect of UV radiation outside the lab or simulated settings. According to the authors, future field studies of real-world implementation of UVGI must consider the various factors within ventilated indoor spaces, including airflow pattern, humidity, air changes per hour, and UV device location, that may affect UV effectiveness.

“Research is needed to provide evidence of the effect of UV radiation along the chain of transmission in non-simulated “real life” settings.”

*Important Notice

medRxiv publishes preliminary scientific reports that are not peer-reviewed and, therefore, should not be regarded as conclusive, guide clinical practice/health-related behavior, or treated as established information.

Journal reference:
Susha Cheriyedath

Written by

Susha Cheriyedath

Susha has a Bachelor of Science (B.Sc.) degree in Chemistry and Master of Science (M.Sc) degree in Biochemistry from the University of Calicut, India. She always had a keen interest in medical and health science. As part of her masters degree, she specialized in Biochemistry, with an emphasis on Microbiology, Physiology, Biotechnology, and Nutrition. In her spare time, she loves to cook up a storm in the kitchen with her super-messy baking experiments.

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