RIO DE JANEIRO, BRAZIL – Despite half a year running from Covid-19, the science working to explain the disease is far from reaching a consensus. One of the most controversial issues is the pathogen’s transmission routes. For the World Health Organization (W.H.O.), the main infection route is the virus-laden drops that escape with coughing, sneezing, etc., and end up in someone else’s mouth, eyes, or nose. Hence the social distancing, the masks, and the handwashing.
However, for months, experts in airborne infections have been urging the W.H.O. to accept that viruses are also suspended in microscopic particles in the air, and can eventually be inhaled by someone close to them within a few minutes. Now 239 experts have published an open letter to health authorities stating that “there is more than enough evidence to enforce the principle of precaution. To control the pandemic, while waiting for a vaccine, all transmission routes must be stopped.”
The letter, which will be published in the Clinical Infectious Diseases journal, outlines some cases where this transmission route seems clear. For instance, the Chinese restaurant where five people from nearby tables were infected by patient zero. In this notorious case, the scientists were able to observe – through the site’s cameras – that there was no interaction between those infected and patient zero.
The infection route had to be the suspended droplets that circled among them during the time they shared at that point in the establishment. The determining factors were no ventilation of the room and recirculated air, leading to the customers’ exposure to infectious agents.
And this is the focal point of the letter: conditions in enclosed spaces are decisive and must be considered. Experts are not uncovering a main or unexpected route; they are merely combining evidence from various scenarios to advise that physical distance is not enough, particularly in enclosed spaces.
There are situations where aerosol contagion occurs, as these small particles can remain suspended and infect someone. Ventilation of closed spaces should be added to the general guidelines and, if possible, events should be relocated to outdoor areas, where the risk of contagion is infinitely lower, as the wind dissolves the particles.
The letter’s authors are concerned that people may think they are fully protected by complying with current W.H.O. recommendations, when in fact additional air precautions are required to reduce the risk of infection, as advised by air conditioning manufacturers. The issue is of utmost relevance now when most countries are beginning to allow indoor activities such as offices, restaurants and even nightclubs, the scientists warn.
In this context, the definition of airborne transmission is important. It is a medical concept established decades ago from studies conducted in the first half of the 20th century, without the technology available to detect microscopic particles. Moreover, the term may seem confusing to people.
The measles virus is airborne: a person entering a room where a patient had been just a few hours earlier is likely to be infected. This scenario has not occurred with Covid-19: there are likely cases of airborne infection, but always with a prolonged exposure (around one hour) to patient zero, who remains present.
As some experts summarize, the measles virus flies like an eagle and the Covid-19 like a chicken. An additional issue in including this means of infection is the complexity of estimating the level of virus present in these tiny droplets – and how many are required to infect someone.
“The problem is not whether airborne transmission is a more or less important route. The key is where. In well-ventilated spaces, this is not a problem because the virus-laden drops are quickly and efficiently eliminated. But if ventilation is inefficient, as in many everyday public areas, this could be the main route,” said Lidia Morawska, one of the first advocates of this transmission route, when she had already written the open letter.
The letter is entitled “It’s Time to Address Covid-19’s Airborne Transmission”. The main author, Morawska, who directs the International Air Quality and Health Laboratory (a standard reference for the W.H.O.) at Queensland University of Technology (Australia), published another article in early April entitled “SARS-CoV-2 Airborne Transmission: The World must Face Reality”. More than three months have passed, and the W.H.O. has done nothing despite the warnings.
“We know the article and we are reviewing its content with our technical experts,” W.H.O. spokesperson Tarik Jasarevic told Reuters. “We have stated several times that we believe airborne transmission is possible, but it is certainly not backed by solid and clear evidence,” Benedetta Allegranzi, the W.H.O. technical leader in infection prevention and control, said to The New York Times.
Source: El País