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New research investigates whether viral particles exist outside self-isolation rooms in households. Jinnaritt Thongruay/EyeEm/Getty Images
  • Researchers investigated whether SARS-CoV-2 particles can be present beyond self-isolation rooms in household settings.
  • They found that SARS-CoV-2 particles can be found in other settings beyond self-isolation rooms and may therefore explain household transmission.
  • Further research is necessary to confirm whether SARS-CoV-2 can spread between individuals via airborne RNA fragments.

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Research shows that vaccines protect against severe symptoms of COVID-19 and are likely to reduce the spread of SARS-CoV-2. However, uncertainty remains when considering public health responses to vaccine-resistant variants or future novel respiratory viruses.

While self-isolation remains a possible strategy, its effectiveness in preventing transmission is questionable. One study found that members of the same house contracted SARS-CoV-2 from each other in 55% of households.

Other research suggests that airborne transmission has links to the spread of SARS-CoV-2. And this is especially the case in households with more crowding, even if personal protective equipment is in use and household members practice isolation.

Knowing if airborne SARS-CoV-2 particles are present beyond isolation rooms in homes could help researchers develop ways to limit the spread of the virus within these settings.

In a recent study, researchers from Rutgers University, New Jersey, investigated whether airborne SARS-CoV-2 particles were present outside of isolation rooms in homes containing one household member with a positive SARS-CoV-2 test result.

They found that aerosols of small respiratory droplets and nuclei containing airborne SARS-CoV-2 RNA were present both inside and outside of home isolation rooms and therefore may put other household members at risk.

“Our indoor air sampling data clearly demonstrated that measurable airborne SARS-CoV2 RNA was present in the air in the homes of most people [with an infection], not only in the isolation room but, importantly, elsewhere in the home.”

Dr. Howard Kipen, lead study author

The study appears in the Annals of the American Thoracic Society.

The researchers recruited 11 adults from 11 different households who had tested positive for SARS-CoV-2 within the previous 7 days. The participants were aged between 31 and 65 years, and five were male.

The researchers collected air samples using polytetrafluoroethylene filters in their homes for 24 hours in two separate rooms, including an isolation room and an adjacent common room.

They noted that there are two primary kinds of airborne particles differentiated by size — from tens of nanometers to tens of microns. The larger kind includes larger respiratory droplets that settle onto surfaces, while the second consists of smaller droplets that may stay suspended in the air for hours, known as aerosols.

The researchers analyzed the air samples for three SARS-CoV-2 genes:

  • the nucleocapsid gene
  • the spike gene
  • the open reading frame-AB region

Altogether, the researchers studied air samples in 11 isolation rooms and nine common rooms. They also recorded how long participants spent in each room.

During the sampling, the participants reported spending between 10 and 24 hours in the isolation room. Additionally, 73% reported spending between 0 and 14 hours in the common room, with 45% spending 0–8 hours in other areas of the home.

From their air sample analyses, the researchers detected at least one SARS-CoV-2 gene in eight out of the eleven homes. They also detected at least two genes in five of the 11 isolation room samples.

The team also detected at least one gene in 66% of common rooms and two genes in 44% of the rooms, with viral aerosols present in 56% of common rooms.

They added that an additional occupant who recently tested positive for SARS-CoV-2 or had symptoms presented in only two out of seven (29%) homes of those with multiple occupants and a common room.

From the results, one theory suggests that viral particles may have spread beyond the self-isolation areas, as not all study participants spent time exclusively in their isolation rooms. However, home architecture may also play a role.

When asked how SARS-CoV-2 particles may have spread in this way, Dr. John Lednicky, Research Professor at the Department for Environmental and Global Health and the University of Florida, said, “At least in the USA, […] heating-ventilation-air-conditioning systems are configured such that air-recirculation between rooms occurs. Air flows provide for air exchanges so that breathing air does not build up excessive amounts of CO2 and bad smells.”

“In air-conditioned homes, the windows are kept shut, and in modern homes, the ceilings are relatively short. When a room is closed off, such as when a self-quarantining person stays in a closed-off room, air currents are stifled and the concentration of virus particles in the air builds up,“ he added.

“When a door is opened, many things happen to perturb air currents. In many cases, air flows out of the closed room into adjacent spaces for various reasons […] Think of a smoking room. The air is filled with smoke in that room, but even when closed, enough airborne smoke particles drift outwards to allow detection (by smell). When the door is open, smoke drifts outward, and it becomes very obvious.”

“Create an air current that goes out from that room (through a fan or through ventilation by the air handling system), and airborne particles can drift out of the isolation room,” he explained.

Dr. Lednicky added that self-isolation works best if the self-isolation room is far away from other living spaces and if there is minimal contact between sick people and others. “Proper” isolation, he said, however, is only possible if one quarantines in a medical facility.

The researchers concluded that aerosols containing SARS-CoV-2 RNA might present an infection risk beyond close contact with other household occupants.

There are some limitations to these findings. Dr. Lendicky said that the study did not answer some key questions:

  • When household members acquire infection from the individual with the virus, does genomic sequencing show that it is the same variant?
  • How long does the virus in the air and on surfaces remain infectious after the person stops their self-isolation period?
  • What about the virus inside a car that a person drives?

He continued to say that it is not yet clear whether the presence of viral RNA in the air can lead to infection.

“Many in the physical sciences think the concentration of virus particles in the air should be constant and that the particles partition equidistantly. Also, many challenge the findings by pointing out that the infectious to noninfectious virus count in nose swabs indicate that most of the virus in [the] air should be noninfectious.”

“The major fallacy [is] that when a nasal swab sample is taken, much of the material consists of nasal epithelial cells that have been ‘scrapped’ off (through the aggressive swabbing action), and cell debris that contains excess virus genomic RNA that is not packaged into virions (complete virus particles)! It is thoroughly incorrect to assume the virus RNA that is detected in swab samples come from virions,” he added.

“I like to remind people that we don’t teach our medical personnel that respiratory pathogens are in coughed or sneezed out cells that come into contact with our mucus membranes. That’s not really what typically happens in real life,” he continued.

“In many reports, authors report they are detecting ‘virus RNA’ in the air. In real life, that is unlikely. RNA is not the most stable material, and the environment contains enzymes that destroy RNA (i.e., RNases),” he concluded.

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