RIO DE JANEIRO, BRAZIL – The tricks used by the novel coronavirus to spread from a single infected person in China in late November to the over 20 million cases on the planet today remain puzzling. The World Health Organization (W.H.O.) maintains that the virus is primarily passed on by respiratory droplets, exhaled when coughing or talking, during close and prolonged contact between two individuals.
Despite pressure from the scientific community, the W.H.O. is reluctant to acknowledge airborne transmission, defined as the spread of the virus suspended in the air for longer times and at greater distances, as is the case with measles and tuberculosis. Pakistani physician Faheem Younus summed it up in May with a masterful statement: “If measles fly like an eagle, the coronavirus flies like a chicken.” However, a new study points out that the chicken may fly farther than some believed.
The coronavirus was found in the air almost five meters away from a symptomatic patient in a room at the University of Florida Hospital in Gainesville (USA), according to a preliminary study published on August 4th. The main new feature in the study, unlike earlier works that had already detected the virus’ genetic material in the air, is that the authors proved that the coronavirus remains “viable” floating almost five meters away from a Covid-19 patient: the virus captured in the air and taken to the laboratory is capable of infecting cells and multiplying within them.
It is infectious. In addition, the viruses captured in suspension are genetically identical to those extracted from the throat of the symptomatic patient. The new study found “the murder weapon,” the evidence that there can be airborne transmission of the coronavirus in enclosed spaces, according to Spanish engineer José Luis Jiménez, an aerosol expert at the University of Colorado (US) who was not involved in the research.
“The implications for public health are many,” say the authors, headed by virologist John Lednicky of the University of Florida. The respiratory droplets, the main culprits of Covid transmission according to the WHO, have a diameter of over five-thousandths of a millimeter and drop to the ground immediately because of their weight, although by evaporating they can produce aerosols, of smaller size, that endure longer in suspension.
“To prevent aerosol transmission, taking measures such as a physical distance of 1.8 meters would not be useful in an indoor area and would provide a false sense of safety, causing exposure to the virus and outbreaks,” the authors stress. Their preliminary study, pending acceptance in the International Society of Infectious Diseases journal, has not yet been exhaustively reviewed by independent researchers.
The W.H.O. is already cautioning about potential airborne coronavirus transmission in hospitals, but only after medical procedures that produce aerosols, such as tracheal intubation of a patient. In the Florida hospital, patients had not been submitted to any of these procedures: they were simply two Covid patients chatting or coughing in a windowless but ventilated room. The air was changed six times an hour with particle filters. In addition to the symptomatic patient, hospitalized the day before, there was another patient about to be discharged.
The air we breathe is infested with all kinds of viruses – which affect humans, animals, vegetables, bacteria – but most are not infectious, due to factors such as ultraviolet light and dryness, so they do not cause disease. The major challenge in the new study was to capture coronaviruses in the air without damaging them, in order to prove in the laboratory that they were still infectious.
The Spanish researcher Arantza Eiguren was involved in the design of the ingenious device that was able to perform this task for the first time. The instrument, a half-meter-high box, sucks air from the room and leads it through a hot section, where the water condenses and adheres to the suspended particles, which are then larger and easier to capture. “It’s very similar to what your lungs do,” says Eiguren, an aerosol specialist with Aerosol Dynamics, based in Berkeley (USA).
According to the researcher, the device detected up to 74 viral particles per liter of air, a “small” amount, perhaps because the room was well ventilated. The scientific community is unaware of the amount of coronavirus required to infect a person. “But if you’re not wearing a mask breathing this air for a while, eventually exposure to the virus can be high,” cautions Eiguren, who, in the past, researched for a decade at the University of California, Los Angeles. “We were able to start shedding some light into the darkness,” celebrates Eiguren, born in 1972 in the Basque town of Elantxobe.
The latest W.H.O. specific report, published on July 9th, was skeptical about the prospect of airborne transmission. “So far, it has not been demonstrated that SARS-CoV-2 is transmitted by this type of aerosol transmission route. Given the potential repercussions of confirming this transmission route, much more research is required,” the document stated.
However, the W.H.O. acknowledged that “it cannot be ruled out that transmission by short-range aerosols has occurred, particularly in specific indoor environments, e.g. places where people are infected, there is crowding and insufficient ventilation over a prolonged period.” The organization mentions suspected outbreaks in crowded and poorly ventilated gyms and restaurants.
A group of 36 international researchers urged the W.H.O. to establish clear guidelines to improve ventilation and thus minimize potential airborne transmission in enclosed areas. Xavier Querol and José Luis Jiménez, from Spain, are two of its signatories. Querol, a geologist at CSIC (Spanish scientific research agency) who specializes in air quality, is very cautious despite the new evidence.
“It’s very dangerous to base ourselves on a single study that can still be rejected during peer review,” he said. The geologist recalls that earlier studies have already found the virus’ genetic material floating in the air in some hospital rooms, for instance in Wuhan, the Chinese city where the pandemic broke out. The evidence is mounting. “I am not criticizing the W.H.O. We are simply laying the updated scientific evidence out on the table. In our group of 36 we are mainly experts in air quality and atmospheric physics. We have an incomplete perspective and we accept that only the W.H.O. has a complete understanding,” says Querol.
Source: El País