Solutions to super-spreading

If we improve the way we clean our indoor air, we could hinder lots of diseases.

At every stage of the pandemic, a disproportionate number of coronavirus infections have been traced to a relatively small number of gatherings, also known as superspreader events. The recent Gridiron dinner, after which over 70 people tested positive, including members of the Biden administration, is just the latest example.

There’s a better way to hold indoor events without masks, and it doesn’t rely on vaccines and rapid tests. Vaccinations can prevent the worst possible outcomes of Covid-19 but cannot always prevent infections. Pre-event testing is imperfect, and for it to be most effective, people need to test right before entering an event.

Putting this much of the onus of infection control on individuals is unlikely to work well to prevent superspreading and lets hosts of large events off the hook for keeping their attendees, workers and others safe. Instead, there are ways that building owners can make indoor environments safer by disinfecting indoor air. One of the best technologies to do so — germicidal ultraviolet light — has been studied for decades and can now be used safely.

The risk of catching diseases transmitted through the air like Covid, measles, tuberculosis and likely many other respiratory infections, including the flu, depends in large part on the amount of infectious viruses — or bacteria in the case of TB — in the air we breathe. The number of these germs in indoor air is controlled by two things: the rate at which infected people in a room exhale germs and the rate at which infectious germs are removed from the air.

Ventilation and filtration can remove germs floating indoors either by blowing them out of the building and replacing the air with fresh outdoor air or by capturing them while moving the indoor air through a filter. At two air changes per hour, which is commonly provided in large buildings, a little more than half of the existing germs are removed every 30 minutes. At six air changes per hour, which is common in hospital rooms and classrooms with multiple portable HEPA air filters, a little more than half of the germs are removed every 10 minutes.

That’s where air disinfection with germicidal ultraviolet light, or GUV, comes in.

GUV can easily and silently kill half of the germs floating in indoor air every two minutes or less. It was developed and tested beginning in the 1930s using some of the same technology in fluorescent light fixtures. It is still commonly used in TB wards, as well as some major hospital systems and homeless shelters.

The conventional GUV technology could cause temporary eye irritation and therefore is mounted above people’s heads in rooms with ceilings around nine feet or higher. It is also best used alongside ceiling fans to make sure germs in a room are blown up into the zone where the GUV can render them harmless.

Newer, commercially available GUV technologies are even safer for skin and do not irritate the eyes. They can be used safely at lower areas of a room and can directly disinfect the air between people sitting at a dinner table.

A major barrier to wider use is that GUV technologies need to be expertly installed and require a set of technical skills different from what’s needed to improve a building’s ventilation and filtration systems (both of which are still critically important). The initial costs for equipment and installation of a highly effective GUV system can often be lower than upgrading or replacing ventilation systems. GUV also disinfects the air faster and with far less electricity than ventilation and filtration, which means it’s a climate-friendly solution for high-risk environments.