Droplets vs. Aerosols: What’s more important with COVID-19 spreads?

Last week, the CDC guidance Regarding SARS-CoV-2 infection, we recognize airborne spread as the main mode of infection.

The new guidance recognizes that inhalation of aerosols, small, lightweight viral particles that can float in the air for extended periods of time, is one way to spread COVID-19. Aerosols can move and infect others even if the infected person is more than 6 feet away.

Following similar changes recently made by the World Health Organization (WHO), CDC guidance recognizes three major routes of SARS-CoV-2 infection: inhalation into the lungs, deposition of droplets on the face. , Or contact with an infected surface. Mediation.

Experts welcomed this change, as many have sought such approval for months.

“One of the most important aspects of recent CDC updates is the final removal of ambiguous” close “terms. This confused the entire debate, “said Dr. Alex Huffman, a university aerosol and bioaerosol expert. Of Denver. Huffman said that “close contact” refers to the distance between people, not the process of communication. Today’s MedPage Previous guidance was unclear, as it did not distinguish that inhalation could occur both short and long distances.

Surface transmission has been thought to be less important, but it remains difficult to distinguish how long-range (aerosol) and proximity (droplet) transmissions are actually causing the spread.The important thing was the expert said Today’s MedPage, Public health measures are to fit data on how the virus spreads and ensure that the intervention is effective.

Evidence of aerial diffusion

People infected with COVID-19 release viral particles during respiratory activities such as breathing, talking, screaming, coughing, sneezing, and singing. However, each of these exhalations can produce different amounts and sizes of breathing particles based on the loudness of the voice someone speaks, the number of deep breaths they take, and the duration of activity.

Large and heavy Flügge Droplets can move up to 6 feet, but then fall to the ground. However, small aerosolized particles can get caught up in the flow of air and travel throughout space, infecting people far away.

Monica Gandhi, MD, MD, an infectious disease expert at the University of California, San Francisco, said: “It is actually the size of the droplet nuclei that defines aerosol-borne and droplet-borne infections. In recognizing COVID-19’s airborne susceptibility, she said,” It is most effective in closed indoor spaces. “Ventilation is one of the most important things to mitigate the virus,” he added.

When an infected individual releases an aerosol, the disease is more likely to spread to poorly ventilated indoor spaces.However, outdoors The virus can spread more easily.. Some epidemiological studies have shown that COVID-19 aerosols can infect others indoors.

When 61 singers participated Chorus practice in Washington At the beginning of the pandemic, one person was infected with COVID-19. However, 2.5 hours of medical care resulted in 52 confirmed or strongly suspected cases of COVID-19, killing 2 people. Researchers hypothesized that long-term loud singing could result in a high continuous stream of aerosol, which could have caused a large outbreak.

Researchers have also identified potential aerial diffusion Chinese restaurant, Among the three families sitting at the table next door. They did not observe close contact or surface infections (except for a few families sitting back-to-back), but the 10 positives dated back to the original infected. Additional analysis shows that in less ventilated rooms Air conditioning flow may have circulated infectious particles To the adjacent table.

Another restaurant study, this is from South KoreaShowed that a teenage girl was infected with a fellow canteen about 20 feet away. Visits to the restaurant only overlapped for 5 minutes, strongly indicating the spread of aerosols.

Aerosol infection was also suspected Slovenian squash coatDue to virus particles that may float in the corridor. Scientists have calculated that it took at least 10 minutes for one infected squash player to leave the athletic facility and for the other player to arrive, but it is possible that he caught COVID-19 from the infected player. He was sexual and didn’t even touch.

Scientists have seen evidence of the aerial spread of the coronavirus, dating back to the first outbreak of SARS in the early 2000s.In a study published by New England Journal of Medicine In 2004, residents of higher floors of apartments exposed to the SARS virus were at increased risk of infection because they assumed that particles in the air would rise with the rising warm air.

It is not clear to prove the number of COVID-19 cases due to aerosol infection compared to other modes, Huffman said. He said it was difficult to clearly separate airborne diffusion from droplet diffusion.

Larger respiratory droplets

Since the beginning of the pandemic, CDC and WHO have claimed that the main route of transmission of SARS-CoV-2 is via large respiratory droplets that can travel a short range of 3 to 6 feet before falling to the ground. doing.

The CDC still states that the entire respiratory fluid is the main route of transmission, but now it involves inhalation of small aerosols and the deposition of the virus by exhalation “splash or spray” on mucous membranes such as the mouth and nose. I make a distinction.Yes Limited evidence of the importance of droplet-to-aerosol -But it is known that larger particles can infect people at close range.

Dr. Adrian Pop, an infectious disease specialist at Huntington Hospital in Northwell Health, New York, said: .. “These droplets tend to fall to the floor or disappear from the surroundings in about 15 or 20 minutes.”

Ravina Kullar, PharmD, and MPH, who speak on behalf of the Infectious Diseases Society of America, say there is no actual number she knows to explain the frequency of SARS-CoV-2 spreading through droplet-to-aerosol. It was. However, she said that droplet propagation occurs more frequently than aerosol propagation, and aerosol propagation occurs more frequently than foamite diffusion.

Low risk of spread through vectors

The CDC has determined that SARS-CoV-2 particles can actually infect the surface. The risk of infection is possible, but authorities have emphasized that the risk is lower than that of droplet or airborne infections.

Findings from mathematical models that estimate the infectivity of vectors show that each contact with a contaminated surface has a 1 in 10,000 chance of infection. In addition, the level of infectivity declines rapidly over time, and surface studies show that after 3 days the infectivity is likely to decline by 99% in an indoor environment. CDC says..

Dr. Lisa Broseau, a research consultant at the University of Minnesota Center for Infectious Diseases Research Policy, said it is most relevant to individuals who are in close direct contact with COVID-19 patients. For example, in a healthcare setting, a healthcare provider may touch the surface of an infected person directly sneezing or coughing before touching his or her eyes, nose, or mouth. In these cases, hand hygiene (and proper PPE) is essential to reduce the risk of infection.

Impact on infection control

Approval of aerosol infections by the CDC could affect our thinking about public health measures, Gandhi said. The definition of aerosol and droplet spread is not always clear, and propagation may be mixed.

“Unlike the black-and-white ones, the definition of aerosolization and droplets is likely to require a major overhaul,” she said. Public health professionals can then provide coordinated precautions based on multiple ways in which the pathogen can spread.

“There are three mitigation strategies that need to be organized individually for each pathogen: distance, ventilation, and masking,” Gandhi said.

Gandhi said wearing a mask that fits snugly in poorly ventilated areas and spending time outdoors (where ventilation is about as good) has proven to be an important infection prevention approach.

“Ventilation has emerged as one of the most important strategies to mitigate a pandemic,” she said.