DHS Creates Tool to Predict How Long SARS-CoV-2 Lives on Surfaces 


Thousands of users accessed the new calculator on its initial day of launch.

Researchers in the Homeland Security Department’s Science and Technology Directorate recently produced and continue to update a predictive modeling tool that forecasts the natural decay of SARS-CoV-2—the virus that causes COVID-19—on surfaces under relevant temperature and humidity conditions. 

The SARS-CoV-2 Natural Decay Calculator pulls insights from in-progress research efforts conducted by S&T’s National Biodefense Analysis and Countermeasures Center. And while it doesn’t directly offer specific guidance, the interactive resource is intended to support response and re-entry efforts and officials’ decisions regarding courses of action to pursue within the facilities they're responsible for.

“We intended the tool to be used by health and safety professionals who are deciding and establishing the procedures and the policies that different places and institutions are going to implement as we return to work, and as we hope to open up,” Lloyd Hough, a microbiologist who also leads the department’s Hazard Awareness and Characterization Technology Center recently told Nextgov. “It'll help people make decisions that are specific to their unique environment.”

Hough detailed what the team’s studies have shown so far about the virus’ deterioration, and he also offered a peek into the tool’s origins, how it works, and how it will be enhanced down the line. 

The agency plays a critical role in producing risk assessments for biological agents, bacteria, viruses and toxins that can be used to intentionally harm the U.S. Hough said the team over the years has created and now uses a “fairly involved process” for calculating the risk each poses. Prior to COVID-19 disrupting the nation, the team applied their comprehensive process to a range of pathogens including anthrax, smallpox, and the plague. The pre-pandemic studies, which hone in on many of their properties and not just those on specific surfaces, also focused on the Ebola virus, the Middle East Respiratory Syndrome virus, and more. 

But, Hough said, in January COVID-19 emerged on the nation’s radar, prompting the S&T team to shift their research focus to its direction. The department rapidly created a Master Questions List on the virus, which is essentially an exhaustive, living document of information gaps about COVID-19. Considering those unknowns, DHS aims to determine how the agency’s capabilities can help close those holes in knowledge. 

“And one of the gaps that was obvious was we don't know how stable this virus is, or even how some of the related viruses are, on surfaces that are important to [Homeland Security] operations and to the operations in the country as a whole,” Hough said. “And so that was kind of the beginning of this whole process.”

The agency in February opted to begin laboratory experiments on the virus, and once gathering a complete dataset, built the formula to predict the decay on relevant surfaces.

“Through internal discussions, we realized that this might actually be helpful to people to be able to easily and quickly see how temperature and humidity have an impact on the virus' stability in certain environments,” Hough said. “And then that was what led to the tool.”

To use the natural decay calculator, users simply select the surface type, and then enter the surrounding temperature and relative humidity. A table depicting the resulting decay then subsequently details the information below. While it currently works for surfaces including stainless steel and ABS plastic, nitrile will come next and more are planned to be included in the near future.

In the briefing with Nextgov, Hough outlined the research that underpins the predictive modeling resource, which is ongoing at an interagency biodefense campus on Fort Detrick in Maryland. He noted that while the effort is supported by many folks who are working remotely given the present conditions, about 10 to 15 scientists must show up every day to embark on the efforts. “They cannot do this work from home,” he said. That lab encompasses many pieces of what Hough called “really specialized equipment,” including environmental chambers that enable scientists to control things inside like temperature, humidity and whether inside components being tested are exposed to sunlight, or other kinds of light. 

“So what we do is we take the virus and we grow it up,” Hough explained. “We get a solution of the virus and then we can put drops of that onto little pieces of surfaces that we care about.”

The team essentially cut out little discs of stainless steel and of ABS plastic, which is the plastic that makes up computer keyboards, telephones and more, for analysis. Researchers are also doing the same with pieces of nitrile, the surface that makes up disposal gloves people wear against germs. Once they put the solution onto those discs, they then test the virus-covered surfaces under different circumstances inside the chamber.

“So we put it in there and we let it bake—we let it incubate for a period of time—and then we collect the virus off of those little discs, after exposing them to those environmental conditions,” Hough said. 

Researchers then plug the information gathered into the tool they’ve built, which incorporates a formula to process results. Hough called it “one of those fancy math equations that you don't pay attention to in high school math” and then added that “those equations allow us to predict within the range of conditions that we've tested.” 

In their initial studies on ABS plastic and stainless steel, Hough said researchers didn’t notice differences between the two surfaces that were statistically significant. However, they did find that “as the temperature gets warmer, and as the humidity gets higher, the virus decays a lot faster,” Hough explained. This means that if the tool is dialed down to 70 degrees in temperature and 20% humidity, it will show that the virus has a half-life of about 15 hours. “But then as you raise the temperature and you raise the humidity, you see that half-life drop down to much fewer [hours],” he said. Hough also noted that the dataset Homeland Security’s team generated is the first, to his knowledge, that enables people to predict decay rates under specific conditions. 

“And we're looking forward to expanding it a little bit further,” he said.

Though the initial work incorporates non-porous surfaces, the team may eventually incorporate more porous materials, such as paper and cardboard. They also plan to address a broader range of temperatures and environmental conditions. Further, the researchers are considering adding the impact of sunlight to determine what happens to SARS-CoV-2 on indoor surfaces, versus those outside. And as the fall and winter months emerge, the team might also evaluate the impact of lower temperatures and humidities.

Still, it appears that the system as it exists now has been leveraged by many since its inception. In terms of metrics, Hough confirmed that 5,000 users tapped into the system on its first day—and more than 13,000 used it within its first three days of public existence.

He also reiterated that the tool is part of a much larger suite of many ongoing data-driven efforts being powered by the directorate, which the team, and agency at-large, hope will resonate even beyond the pandemic. 

“The reason that we're here is to help respond to this outbreak and to develop the data that is needed—wherever that might be, and whatever that might be—to help resolve this as quickly as possible, so that we can return to normal as soon as possible,” Hough said.