Ernst teaches statistics at St. Cloud State University. But the pandemic has turned him, like many others, into a COVID-19 warrior. This year, in hopes of helping his loved ones stay healthy over the holiday, he built a do-it-yourself air cleaning device known as a "Corsi-Rosenthal box" and brought it along.

"They're easy to build. They filter a lot of air quickly. The air flow is quite good. The only downside is the sound, the noise. But if you're at a gathering where things are noisy, it's not a big deal," Ernst said. "We had a bunch of people sitting around watching football. This thing was right in the middle of that and it was not an issue at all."

With two more big holidays looming, Minnesotans ought to follow Ernst's public-health-minded lead and build their own DIY device, a sensible step that will pay off with cleaner air throughout the coming year. Corsi-Rosenthal boxes, named for a University of California-Davis engineering dean and the CEO of a Texas air filter company, are often less expensive than brand-name air purifiers. But like them, these home-built devices can reduce exposure to airborne pathogens.

It's a timely opportunity for those looking for a new way to ramp up the fight against a still-circulating virus. The COVID pandemic isn't over, with cases and hospitalizations ticking up nationally. Influenza and other seasonal respiratory viruses also arrived early this year.

Regrettably, the holidays can put people on a collision course with these potentially serious illnesses. Indoor gatherings and crowded spaces necessitated by travel and colder weather can create ideal conditions for viral transmission.

Vaccines for COVID and influenza remain medicine's most potent tools against the severe sickness these viruses can cause. But throughout the pandemic, medical experts have emphasized a layered approach of protective measures.

The Corsi-Rosenthal box is not a replacement for the vaccine, masking, testing or other precautions. It's another way to safeguard family and friends, with items needed to build it easily found at most hardware stores. The main components: a 20-inch box fan, MERV 13 air filters, duct tape and some cardboard (typically cut from the fan's packaging).

While there are varying designs, the most up-to-date iteration recommended by the UC-Davis involves duct-taping four filters together to create a cube and then attaching a box fan on top. Instructions and a helpful video are available online at tinyurl.com/BuildCRboxfilter.

Turning on the fan circulates air. Air flows through the MERV 13 filters, which in turn remove airborne virus particles, dust, allergens and other pollutants from the air. Sealing the edges with duct tape and covering the fan's edges with a cardboard shroud help improve efficiency.

UC-Davis estimates the cost of building one at around $65. "So about one-quarter of the cost of a really good HEPA air cleaner to build a Corsi-Rosenthal box, which is more effective than that much more expensive air cleaner," the university's online information states. The device is "incredibly effective for lowering the levels of virus-laden aerosol particles in classroom air, in an office suite air, in the air in your home or apartment."

Ernst estimated that it took him under two hours to make one, and added that he could do it faster a second time. Others might need more time because part of the fun for many is decorating the devices. Groups promoting the boxes' use in classrooms and day-care facilities, for example, have made the boxes look like robots.

For a White Bear Lake family, assembling a box was a father-daughter project. Matt Aliota, a University of Minnesota virology professor, was looking for a way to improve the safety of classrooms and other congregate settings. He found the Corsi-Rosenthal box's DIY aspect appealing. "If you can duct tape something, you should be able to handle it," he said.

He and his daughter built a box for her third-grade classroom. Among her contributions: picking out brightly colored duct tape and explaining to the other students why the box is in the classroom and what it does.

Other families should take note: The Corsi-Rosenthal box isn't just a good idea for the holidays; it can keep indoor air cleaner year-round.