Healthcare workers are advised to stay 1.5 metres away from COVID-19 patients — an adaptation of hospital guidelines which state that 1–2 metres is a safe distance from an infectious patient. However, a study by UNSW and MIT examined the data upon which this rule is based and revealed that respiratory droplets which may carry a virus can travel beyond the 1- to 2-metre safety zone. NATIONAL SAFETY takes a look at its findings and implications for frontline health workers.
For the study, researchers examined the available literature on the horizontal distance travelled by respiratory droplets, with findings from the study published in the Journal of Infectious Diseases. Findings revealed that the available scientific evidence does not support the assumption that contamination from symptomatic patients would only occur within a 1- to 2-metre safe distance for spatial separation. The authors argue that the 1- to 2-metre rule, which is part of the guidelines set by the World Health Organization (WHO) and other agencies, dates back to the 1930s, and is founded on the belief that large droplets emitted by exhalations — or those able to be seen or felt when someone coughs or sneezes on you — do not travel beyond this distance, and do not remain suspended in the air.
The researchers reviewed 10 studies on the distance travelled by droplets from various types of exhalations, with eight studies revealing that droplets travelled more than two metres and up to eight metres from the person emitting them. Findings from the study have implications for guidelines on social distancing. “Up until now it has been assumed that the large droplets expelled from exhalations fall to the ground quickly,” Professor Raina MacIntyre, Biosecurity Program Head at the Kirby Institute, said. “The guidance we are given for social distancing of 1.5 metres is based on the belief that 1–2 metres is a safe distance to avoid being sprayed by large droplets and that these droplets would be the main emissions containing the virus and able to cause disease.
“But the body of evidence shows that droplets can be expelled further than two metres. Smaller particles that can’t be seen or felt may remain suspended in a ‘cloud’ and then carried for hours in ambient air, so they can end up travelling much longer distances,” Professor MacIntyre said. Professor Lydia Bourouiba, Director of MIT’s Fluid Dynamics of Disease Transmission Laboratory, revealed that the gas turbulent cloud identified in previous MIT studies on violent exhalations suggests that transmission routes of respiratory diseases cannot be separated into droplet versus airborne transmission.
“The evidence we reviewed in the present study on distances reached by a range of exhalations — coupled with the SARS-CoV-2-specific studies reporting the virus being identified up to 4 metres from a patient or in air vents — are consistent with the cloud dynamics of exhalations,” Professor Bourouiba said. “This means the virus can have an extended range of contamination in the air compared to the short-range, surface-only contamination assumed from current definitions of the droplet route of transmission. Taken together with evidence of possible persistence of infectiousness of the virus for a few hours in laboratory conditions, the study calls for greater precautions with clear implications for protection of healthcare workers.”
Research suggests that the continuum between droplets and airborne transmission of the virus means the two different levels of protection currently advised for healthcare workers treating coronavirus (COVID-19) patients need re-evaluating. In both cases, medical staff wear gloves, gowns and eye protection, but use surgical masks to protect against droplets, while respirator masks (N95 or P2) are worn for airborne viruses. However, evidence suggests respirators should be the first and only choice for frontline health professionals. “The study will give clinicians a more comprehensive picture of the mechanisms underlying infection transmission via exhalations, which is important at this time of COVID-19 pandemic and beyond,” said Prateek Bahl, lead author of the study.
UNSW Engineering’s Professor Con Doolan explains the complex physics of droplets and aerosols: “When you sneeze or cough, the droplets are created in random ways and can travel much further than we previously thought. We really don’t know how the droplets interact with surgical masks and until we understand that, then we should be using respirator masks.” This study could clarify the discrepancies in recommendations from various international and governmental organisations as countries struggle to cope with the COVID-19 threat. WHO recommends that healthcare workers caring for suspected COVID-19 patients should adopt precautions against contact and droplet transmission of the virus. The US Centre for Disease Control (CDC) initially recommended adopting precautions against airborne transmission.
Professor MacIntyre said that if the evidence suggests droplets can travel further than 2 metres, then “the air inside a standard hospital room could be contaminated beyond that distance. Given the high case fatality rate and documented deaths of health workers from COVID-19, the ‘precautionary principle’ and use of a respirator is warranted. The global shortages of personal protective equipment should ideally not drive policy. We should instead focus on scaling up PPE manufacturing capacity in all countries.” There is limited scientific data informing spatial separation guidelines, the study suggests, and growing evidence that also suggests that current guidelines pertaining to SARS-CoV-2 would benefit from being revisited.
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