Should I Worry About Coronavirus on My Shoes?

Making sense of a new CDC report about your soles

Recent headlines about a new Centers for Disease Control and Prevention report about the coronavirus and your shoes may have you using your doormat more vigorously than usual. “CDC Study Shows Coronavirus Can Live on Floors, Shoes,” reads one; “We regret to inform you, your sneakers may have COVID-19,” announces another.

While there’s no question that cleanliness is absolutely crucial these days, the paper and its findings warrant a closer look. The paper, written by researchers in Wuhan, China, is an early release (meaning it’s not considered final yet) in the CDC journal Emerging Infectious Diseases. The paper is focused on determining how SARS-CoV-2, the virus that causes Covid-19, is distributed in the air and on surfaces — specifically in the intensive care unit and general ward of a Wuhan hospital treating Covid-19 patients.

It’s well established that the virus primarily spreads through close contact and respiratory droplets, tiny spheres of liquid expelled when a person coughs, talks, or sneezes. Determining how these droplets accumulate and move in the hospital is important because it can guide cleaning strategies meant to keep patients and health care workers safe.

So, the team tested a range of surfaces in the hospital: floors, computer mice, trash cans, sickbed handrails, patient masks, personal protective equipment, air outlets, and, of course, shoes. Generally, more surfaces in the ICU tested positive than in the general ward — including the soles of the shoes of the ICU medical staff. Half of the samples taken from ICU medical staff shoes tested positive for the virus.

It’s worth considering what testing “positive” in this case really means. The researchers tested specifically for two SARS-CoV-19 genes, one for a stretch of genetic material called an “open reading frame” and another for the N protein, one of the virus’s key structures. A positive result meant that they found pieces of RNA, the virus’s genetic material, corresponding to those genes on the surface they sampled. But it doesn’t necessarily mean that those traces were infectious. One limitation the team notes is that “the results of the nucleic acid test do not indicate the amount of viable virus.”

A similar caveat came up a few weeks ago when the CDC published a report suggesting that traces of the coronavirus lived on surfaces…