Australian optometrists are being advised to consider improving airflow and ventilation within their practices after the World Health Organization acknowledged it could not rule out the possibility of airborne transmission of COVID-19 in indoor settings.
With the true extent of asymptomatic infection not yet known, the WHO’s updated position has potential implications for eyecare professionals and came just days before a Medical Journal of Australia article outlined the evidence for airborne transmission. It estimated there have been 500 health worker infections in Australia, despite there being no national reporting system.
In response to these developments, Optometry Australia said optometrists should consider ventilation, including opening windows – or at least the consulting room door – where practical to improve airflow. This is in addition to previous advice that all optometrists in Greater Melbourne and Mitchell Shire seeing any patient for any reason should wear a standard surgical mask.
The organisation also points to Australian Department of Health Coronavirus Disease (COVID-19) Social distancing guidelines that suggest considering “opening windows and adjusting air conditioning for more ventilation”.
“Obviously in most optometry outpatient settings there is limited control over ventilation, and ventilation standards are not the same as controlled hospital settings,” OA noted, with more information available here.
Airborne transmission possible
In its most definitive statement on COVID-19 spread published on 9 July, the WHO said airborne transmission was possible in some indoor settings such as crowded and inadequately ventilated spaces over a prolonged period of time.
Airborne transmission is caused by the dissemination of droplet nuclei (aerosols) measuring <5μm that remain infectious when suspended in air over long distances and a long period of time.
Until now, the WHO said that airborne transmission of the virus only occurred in healthcare settings during aerosol generating procedures. (RANZCO states that phacoemulsification, vitrectomy, laser refractive surgery and oculoplastic surgery where cautery or high-speed instruments are used, may be aerosol generating procedures).
It has maintained that the primary form of coronavirus transmission is via respiratory droplets passed through close contact with people who are infected. It is also likely that people can become infected touching contaminated surfaces.
While it could not rule out airborne transmission in poorly ventilated indoor locations such as choir practice, restaurants or fitness classes, it stressed investigations of these clusters suggest that droplet and fomite (contaminated surfaces) transmission could also explain the spread in these circumstances.
The WHO noted that some studies conducted in healthcare settings where symptomatic COVID-19 patients were cared for, but where aerosol generating procedures were not performed, reported the presence of SARS-CoV-2 RNA in air samples. However, other similar investigations in both healthcare and non-healthcare settings did not reach the same finding.
“Further studies are needed to determine whether it is possible to detect viable SARS-CoV-2 in air samples from settings where no procedures that generate aerosols are performed and what role aerosols might play in transmission,” the WHO noted.
Strength of evidence questioned
In an article published in the Medical Journal of Australia on 14 July, lead author Professor Raina MacIntyre, an infectious diseases expert from the University of New South Wales, said the initial proclamation that SARS-CoV-2 is spread by droplets and contact was not based on strong evidence, and there is no data quantifying the different modes of potential transmission.
“The guidelines for protection of healthcare workers in Australia state that a medical mask is indicated for routine care of COVID-19 patients, and a respirator only for aerosol-generating procedures. These guidelines are not aligned with the growing body of scientific evidence around transmission and prevention of SARS-CoV-2 infection,” the article said.
In their work that outlines the evidence of airborne transmission, MacIntyre and her colleagues note there were more than 500 health worker infections in Australia by July, but no national reporting on health worker infections, and lack of transparency in attribution of the source of infection.
Importantly, they say that guidelines on ‘droplet precautions’ (masks) and ‘airborne precautions’ (respirators) assume that respiratory emissions can be separated into mutually exclusive groups – droplet and airborne spread.
But this assumption is based on limited data from the 1930s, with newer studies showing that droplets and aerosol particles exist in a continuum; a single large droplet may reduce in diameter and become airborne during its trajectory, because of evaporation.
“We suggest that all health workers treating COVID-19 patients be provided airborne precautions, that … the precautionary principle be applied to health worker protection. We also require transparent national reporting of health worker infections. This is particularly urgent as numerous health worker infections have been reported in hospitals in Victoria during Australia’s resurgence of COVID-19.”
Exception rather than the rule
In an article written for The Journal of the American Medical Association on 13 July, Dr Michael Klompas and his colleagues from the Harvard Medical School said demonstrating that speaking and coughing can generate aerosols or that it is possible to recover viral RNA from air does not prove aerosol-based transmission.
“Proponents of aerosol-based transmission cite well-documented clusters of infections among choir participants, restaurant patrons, and office workers sharing closed indoor spaces. However, based on the reproduction number for SARS-CoV-2, these events appear to be the exception rather than the rule,” they said.
“It is impossible to conclude that aerosol-based transmission never occurs and it is perfectly understandable that many prefer to err on the side of caution, particularly in healthcare settings when caring for patients with suspected or confirmed COVID-19. However, the balance of currently available evidence suggests that long-range aerosol-based transmission is not the dominant mode of SARS-CoV-2 transmission.”
