The U.S. Centers for Disease Control and Prevention (CDC) today released new guidelines on the use of ventilation strategies to reduce the risk of exposure to the SARS-CoV2 coronavirus in indoor settings.

Indoor environments have long been known to be riskier for the transmission of viral particles than outdoor environments, largely due to relative lack of airflow and confined spaces, allowing viral particles to accumulate more than they typically do outside.

Scientists have been arguing since the start of the pandemic that ventilation strategies are a vital way to mitigate the risk of infection in these environments, but the majority of public health communication in the U.S. has focused on physical distancing, handwashing and masking. All of these are doubtlessly important, but the new CDC advice on ventilation hopes to add an additional layer of mitigation to reduce risk of transmission in indoor environments.

“These types of interventions are exactly what experts have been recommending for months,” said Linsey Marr, Professor of Civil and Environmental Engineering at Virginia Tech, who studies viruses in the air. “It is wonderful to see the CDC provide powerful, accurate guidance that can easily be applied in homes, workplaces, and schools over a range of budget options,” Marr added.

The guidelines present a list of ventilation interventions which, if applied properly, can help to reduce the concentration of viral particles in the air. However, they do stress that ventilation strategies are just one “tool in the mitigation toolbox” and should be implemented with others at the same time for maximum effect and that ventilation alone cannot eliminate the risk of viral transmission completely.

Some of the interventions can be done at no, or minimal cost, such as opening windows and doors in areas where climate allows and positioning fans strategically near open windows to increase airflow. Other suggestions include shutting off thermostatically-controlled ventilation and keeping fans on constantly.

The CDC guidelines are intended to be universally applicable across indoor environments, but concede that making ventilation strategies work in each individual circumstance is more complex and will change depending on building or room type, occupancy, the activities taking place in the building and seasonal changes.

Some of the suggested interventions come with moderate costs and are likely more targeted at businesses and workplaces, such as high-efficiency particulate air (HEPA) fans and filtration systems, which can filter out virus particles and ultraviolet germicidal irradiation (UVGI) technology, which can inactivate viruses like SARS-CoV2 by using UV light.

The guidelines list example costs for these systems, per room of around $500 for the HEPA systems and $1500 for upper room UVGI. The new guidelines have been welcomed by many scientists who have been campaigning for ventilation to be a priority for reducing the risk of infection in indoor environments.

“Now that CDC has offered guidance on this topic, it will be harder for people to ignore the importance of ensuring good ventilation in buildings,” said Marr.

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