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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.

Days after Twitter accounts of several billionaires were hacked to engineer a crypto scam, Twitter on Saturday said it is embarrassed, disappointed and, more than anything, sorry for what happened with some of its high-profile users as attackers successfully manipulated its employees and used their credentials to access internal systems, including getting through the two-factor protections.

In the first detailed summary of the "social engineering attack" via a crypto scam that hit at least 130 users this week, Twitter said for 45 of those accounts, the attackers were able to initiate a password reset, login to the account and send Tweets.

"We are continuing our forensic review of all of the accounts to confirm all actions that may have been taken. In addition, we believe they may have attempted to sell some of the usernames," the micro-blogging platform said in a statement.

For up to eight of the Twitter accounts involved, the attackers took the additional step of downloading the account's information via "Your Twitter Data" tool.

This is a tool that is meant to provide an account owner with a summary of their Twitter account details and activity.

"We are reaching out directly to any account owner where we know this to be true. None of the eight were verified accounts," said Twitter.

The company said the attackers were not able to view previous account passwords, as those are not stored in plain text or available through the tools used in the attack.

"Attackers were able to view personal information including email addresses and phone numbers, which are displayed to some users of our internal support tools," informed Twitter.

In cases where an account was taken over by the attacker, they may have been able to view additional information, Twitter added, saying its forensic investigation of these activities was still ongoing.

"We are actively working on communicating directly with the account-holders that were impacted".

The company said it will soon restore access for all account owners who may still be locked out as a result of the remediation efforts.

The New York Times reported on Friday that the Twitter crypto scam can be traced back to a group of hackers who congregate online at OGusers.com, a username-swapping community where people buy and sell coveted online handles.

The report said that the Twitter hack is not from Russian, Chinese or North Korean hackers but was done by a group of young people, "one of whom says he lives at home with his mother".

New Delhi, Mar 19: Lawyer of Mukesh Singh, who is one of the four death row convicts in the Nirbhaya gang-rape and murder case, on Thursday mentioned a petition before the Registrar of the Supreme Court seeking an urgent hearing in the matter.

Advocate Manohar Lal Sharma, through the petition, sought directions to bring call record, documents and reports of his client through any probe agency and passed appropriate directions and measure to ensure justice in the matter.

The petition, however, has not sought a stay on the execution, which is scheduled for the morning of March 20. The petition is likely to be taken up for hearing today.

Earlier today, the apex court dismissed the curative petition of Pawan Gupta, another convict in the matter, who claimed juvenility at the time of the crime.

This comes as the four convicts -- Mukesh Singh, Akshay Singh Thakur, Vinay Sharma and Pawan Gupta -- are scheduled to be hanged at 5.30 am on March 20.

Meanwhile, several other petitions are also pending in the matter in different courts.

The case pertains to the brutal gang-rape and killing of a 23-year-old paramedical student in a moving bus on the night of December 16, 2012, by six people including a juvenile in the national capital. The woman had died at a Singapore hospital a few days later.