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The coronavirus can stay aloft for hours in tiny droplets in stagnant air, infecting people as they inhale, mounting scientific evidence suggests.

This risk is highest in crowded indoor spaces with poor ventilation, and may help explain superspreading events reported in meatpacking plants, churches and restaurants.

It’s unclear how often the virus is spread via these tiny droplets, or aerosols, compared with larger droplets that are expelled when a sick person coughs or sneezes, or transmitted through contact with contaminated surfaces, said Linsey Marr, an aerosol expert at Virginia Tech.

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Aerosols are released even when a person without symptoms exhales, talks or sings, according to Marr and more than 200 other experts, who have outlined the evidence in an open letter to the World Health Organization.

What is clear, they said, is that people should consider minimizing time indoors with people outside their families. Schools, nursing homes and businesses should consider adding powerful new air filters and ultraviolet lights that can kill airborne viruses.

What does it mean for a virus to be airborne?

For a virus to be airborne means that it can be carried through the air in a viable form. For most pathogens, this is a yes-no scenario. HIV, too delicate to survive outside the body, is not airborne. Measles is airborne, and dangerously so: It can survive in the air for up to two hours.

For the coronavirus, the definition has been more complicated. Experts agree that the virus does not travel long distances or remain viable outdoors. But evidence suggests it can traverse the length of a room and, in one set of experimental conditions, remain viable for perhaps three hours.

How are aerosols different from droplets?

Aerosols are droplets, droplets are aerosols — they do not differ except in size. Scientists sometimes refer to droplets fewer than 5 microns in diameter as aerosols. (By comparison, a red blood cell is about 5 microns in diameter; a human hair is about 50 microns wide.)

From the start of the pandemic, the WHO and other public health organizations have focused on the virus’s ability to spread through large droplets that are expelled when a symptomatic person coughs or sneezes.

These droplets are heavy, relatively speaking, and fall quickly to the floor or onto a surface that others might touch. This is why public health agencies have recommended maintaining a distance of at least 6 feet from others, and frequent hand washing.

But some experts have said for months that infected people also are releasing aerosols when they cough and sneeze. More important, they expel aerosols even when they breathe, talk or sing, especially with some exertion.

Scientists know now that people can spread the virus even in the absence of symptoms — without coughing or sneezing — and aerosols might explain that phenomenon.

Because aerosols are smaller, they contain much less virus than droplets do. But because they are lighter, they can linger in the air for hours, especially in the absence of fresh air. In a crowded indoor space, a single infected person can release enough aerosolized virus over time to infect many people, perhaps seeding a superspreader event.

For droplets to be responsible for that kind of spread, a single person would have to be within a few feet of all the other people, or to have contaminated an object that everyone else touched. All that seems unlikely to many experts: “I have to do too many mental gymnastics to explain those other routes of transmission compared to aerosol transmission, which is much simpler,” Marr said.

Can I stop worrying about physical distancing and washing my hands?

Physical distancing is still very important. The closer you are to an infected person, the more aerosols and droplets you may be exposed to. Washing your hands often is still a good idea.

What’s new is that those two things may not be enough. “We should be placing as much emphasis on masks and ventilation as we do with hand washing,” Marr said. “As far as we can tell, this is equally important, if not more important.”

Should I begin wearing a hospital-grade mask indoors? And how long is too long to stay indoors?

Health care workers may all need to wear N95 masks, which filter out most aerosols. At the moment, they are advised to do so only when engaged in certain medical procedures that are thought to produce aerosols.

For the rest of us, cloth face masks will still greatly reduce risk, as long as most people wear them. At home, when you’re with your own family or with roommates you know to be careful, masks are still not necessary. But it is a good idea to wear them in other indoor spaces, experts said.

As for how long is safe, that is frustratingly tough to answer. A lot depends on whether the room is too crowded to allow for a safe distance from others and whether there is fresh air circulating through the room.

What does airborne transmission mean for reopening schools and colleges?

This is a matter of intense debate. Many schools are poorly ventilated and are too poorly funded to invest in new filtration systems. “There is a huge vulnerability to infection transmission via aerosols in schools,” said Don Milton, an aerosol expert at the University of Maryland.

Most children younger than 12 seem to have only mild symptoms, if any, so elementary schools may get by. “So far, we don’t have evidence that elementary schools will be a problem, but the upper grades, I think, would be more likely to be a problem,” Milton said.

College dorms and classrooms are also cause for concern.

Milton said the government should think of long-term solutions for these problems. Having public schools closed “clogs up the whole economy, and it’s a major vulnerability,” he said.

“Until we understand how this is part of our national defense, and fund it appropriately, we’re going to remain extremely vulnerable to these kinds of biological threats.”

What are some things I can do to minimize the risks?

Do as much as you can outdoors. Despite the many photos of people at beaches, even a somewhat crowded beach, especially on a breezy day, is likely to be safer than a pub or an indoor restaurant with recycled air.

But even outdoors, wear a mask if you are likely to be close to others for an extended period.

When indoors, one simple thing people can do is to “open their windows and doors whenever possible,” Marr said. You can also upgrade the filters in your home air-conditioning systems, or adjust the settings to use more outdoor air rather than recirculated air.

Public buildings and businesses may want to invest in air purifiers and ultraviolet lights that can kill the virus. Despite their reputation, elevators may not be a big risk, Milton said, compared with public bathrooms or offices with stagnant air where you may spend a long time.

If none of those things are possible, try to minimize the time you spend in an indoor space, especially without a mask. The longer you spend inside, the greater the dose of virus you might inhale.

New Delhi, May 15: A group of doctors from the AIIMS, Raipur has recommended restrictions on the use of mobile phones in healthcare institutions amid the COVID-19 pandemic, warning that such devices can be a potential carrier of the virus and lead to infection among healthcare workers.

In a commentary published in the BMJ Global Health journal, the doctors stated that mobile phone surfaces are a peculiar 'high-risk' surface, which can directly come in contact with the face or mouth, even if hands are properly washed and one study indicates that some healthcare workers use phones every 15 minutes to two hours.

Though there have been many significant guidelines from various health organisations like the WHO and CDC focusing on prevention and control of disease, the commentary highlighted "there is no mention of or focus on mobile phones in these guidelines, including the WHO infection control and prevention guidelines, which recommends the use of handwashing".

In healthcare facilities, phones are used to communicate with other health care workers, look up recent medical guidelines, research drug interactions, understand adverse events and side effects, conduct telemedicine appointments and track patients among others, stated the document.

The document has been authored by Dr Vineet Kumar Pathak, Dr Sunil Kumar Panigrahi, Dr M Mohan Kumar, Dr Utsav Raj and Dr Karpaga Priya P from the Department of Community and Family Medicine.

"In their tendency to come in direct contact with the face, nose or eyes in healthcare settings, mobile phones are perhaps second only to masks, caps or goggles," the authors said.

"However, they are neither disposable nor washable like these other three, thus warranting disinfection. Mobile phones can effectively negate hand hygiene... There is growing evidence that mobile phones are a potential vector for pathogenic organisms," they said.

It is the need of the hour to address proper hygienic use of mobile phones in healthcare settings. In a study in India, almost 100 per cent of health workers of a tertiary care hospital used mobile phones in the hospital, but only 10 per cent of them had at any time wiped their mobile phones clean, the commentary published on April 22 said.

"The safest thing to do is to consider your phone as an extension of your hand, so remember you are transferring whatever is on your phone to your hand," Dr Pathak said.

Amidst the ongoing pandemic, two biggest mobile phone companies have uploaded their user support guidelines, saying that 70 pc isopropyl alcohol or Clorox Disinfecting Wipes can be used to gently wipe the exterior surface of phones in switched-off mode.

However, in doing so, the use of bleach or entry of moisture through any of the openings must be avoided, and any harsh chemical may damage the oleophobic screen, leading to damage in the touch screen sensitivity of the phone, the article stated.

Mobile phones are one of the most highly touched surfaces according to the Centers for Disease Control and Prevention (CDC), along with counters, tabletops, doorknobs, bathroom fixtures, toilets, keyboards, tablets and bedside tables.

The doctors recommended restriction on mobile phone usage in healthcare settings like hospital wards, ICUs and operation theatres, while advocating the use of headphones to prevent contact with the face while talking.

There should be no sharing of mobile phones, headphones or headsets of any kind. In addition, where available, the use of interdepartmental intercom facility may be promoted.

"Although hand hygiene and mobile phone use by a person are not mutually exclusive, it is high time to acknowledge the potential role of mobile phones in disease transmission cascade and to take evidence-based appropriate actions. This is especially important, given the ongoing COVID-19 pandemic," the authors said.

They said it is necessary for government agencies and the WHO to generate public awareness and to formulate suitable information, education and communication material on mobile phone hygiene, especially in healthcare settings.

AIIMS, New Delhi, Resident Doctors' Association (RDA) General Secretary, Dr Srinivas Rajkumar T said even outside health care settings, people should pay special attention to the usage of mobile phones as they carry them to all places.

"Phone and computer peripherals like keyboard, mouse, etc. should be covered with transparent plastic covers which can be cleaned without interfering with their function. Cleaning hands by soap or alcohol-based hand sanitizer before and after contact with phone and between contact with other surfaces can decrease the risk of potential transmission.

"Using a handsfree headset, dedicated operator/assistant per ward handling the communication via common line in hospitals while on duty can enable communication without compromising safety," Dr Srinivas said.