Researchers have found that the genetic material from the virus that causes COVID-19 can be extracted from indoor dust long after the virus is inactive, which could prove a useful tool for monitoring outbreaks of the disease.
Their study, published April 13 in mSystems, suggests that while dust cannot be used to test for living viruses, dust monitoring could provide an ideal compromise between wastewater testing, which is inexpensive but nonspecific, and individual testing, which is precise but costly.
"We think that this is going to be really helpful in buildings such as congregate care facilities, dormitories, prisons, anywhere where you're concerned that you really want to catch an outbreak early," said senior author Karen Dannemiller, an assistant professor of engineering at Ohio State University. "Then you can identify that, maybe we do need to do some individual testing because we know that there have been cases here."
While Dannemiller had not worked very much on viruses previously, focusing instead on causes of childhood asthma, the pandemic offered her an opportunity to collaborate with colleagues and students across departments to contribute to the fight against COVID-19.
"We're really thankful for all the health care heroes out there, everybody really jumping in and doing their part," Dannemiller said. "So we wanted to do what we could to try to understand what was going on in the indoor environment."
Airborne viruses like the flu have been recently shown to live on dust, but dust-collecting is generally not used as a method for monitoring live outbreaks of infectious diseases.
The idea emerged after first author Nicole Renninger, a master's student in Dannemiller's lab, had been working on extracting RNA, the genetic material found inside viruses, from dust.
"Prior to all this, we wanted to have a better method to measure RNA and dust because we wanted to understand gene expression of the microbes in the dust samples," said Dannemiller.
The process of extracting RNA from dust consists of a complex series of lab-controlled biochemical reactions. The RNA can then be tested for a specific gene found in the virus.
"This may sound trivial and boring," Dannemiller said, "but it's actually very interesting because RNA is actually really, really difficult to get out of dust."
For their study, the researchers used dust from the bedrooms of people who had tested positive for COVID-19. They used surface swabs and samples from passive collectors such as carpet, as well as "bulk dust," which was collected from vacuum cleaners.
They found that 89% of bulk dust and 55% of surface swabs contained RNA from SARS-Cov-2, the virus that causes COVID-19. They also found the RNA in the bulk dust did not appreciably decay over four weeks, even though the rooms had been disinfected prior to vacuuming.
"One thing that surprised us was that the RNA persisted in the dust for such a long period of time," Dannemiller said. "We were really surprised about that because other RNA in dust tends not to last very long. But the viral RNA is protected within the envelope in the capsid."
This capsid, the outer shell of the virus, is why the RNA can persist long after the virus has died. The RNA persists for so long in the dust that dust monitoring cannot currently be used to test for live viruses.
"We did not measure infectivity; none of this means that the virus is infectious in the dust at all," Dannemiller said. "It's just kind of a leftover viral fragment that we're measuring."
Because the present study was simply testing the concept, the team knew ahead of time that the rooms from which the samples were taken had contained positive cases. The researchers are now conducting a pilot study in which they plan to test the method's accuracy more realistically by using samples that may or may not contain viral RNA.
The researchers are hopeful that their method will not only be effective, but easy to implement. Every time we vacuum our homes, we could be collecting samples to monitor COVID-19.
"I think that one of the potential benefits of a technique like this is you're already collecting us dust samples," Dannemiller said. "We can just use that. So I could see people in the future shipping off their vacuum bag once a week, just to keep an idea of what's going on."
The study, "Indoor dust as a matrix for surveillance of COVID-19," published April 13 in mSystems, was authored by Nicole Renninger, Nicholas Nastasi, Ashleigh Bope, Samuel J. Cochran, Sarah R. Haines, Neeraja Balasubrahmaniam, Katelyn Stuart, Natalie M. Hull and Karen C. Dannemiller, Ohio State University; and Aaron Bivins and Kyle Bibby, University of Notre Dame.