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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.

Bengaluru, Mar 12: Imarti Devi, who recently resigned as Congress MLA from Madhya Pradesh, on Wednesday said that she was happy with Jyotiraditya Scindia's decision to join the BJP.

Imarti said: "All 22 MLAs are here (in Bengaluru) on their own. We're happy that Scindiaji has taken this decision. I'll always stay with him even if I had to jump in a well."

"When we were in the Congress, Kamal Nathji never heard us," she said.

Another rebel leader and former minister Mahendra Singh Sisodia said: "Betrayal is not done by Jyotiraditya Scindia. Instead, betrayal was done by the Congress and Kamal Nathji."

"Congress betrayed the people of Madhya Pradesh. We are with Jyotiraditya Scindia," he said.

Riyadh, Mar 6: Saudi Arabia on Thursday emptied Islam's holiest site for sterilisation over fears of the new coronavirus, an unprecedented shutdown state media said will last while the year-round Umrah pilgrimage is suspended.

The kingdom halted the pilgrimage for its own citizens and residents on Wednesday, on top of restrictions announced last week on foreign pilgrims to stop the disease from spreading.

State television relayed images of an empty white-tiled area surrounding the Kaaba -- a large black cube structure inside Mecca's Grand Mosque -- which is usually packed with tens of thousands of pilgrims.

As a "precautionary measure", the area will remain closed as long as the umrah suspension lasts but prayers will be allowed inside the mosque, state-run Saudi Press Agency cited a mosque official as saying.

Additionally, the Grand Mosque and the Prophet's Mosque in the city of Medina will be closed an hour after the evening "Isha" prayer and will reopen an hour before the dawn "Fajr" prayer to allow cleaning and sterilisation, the official added.

A group of cleaners was seen scrubbing and mopping the tiles around the Kaaba, a structure draped in gold-embroidered gold cloth towards which Muslims around the world pray.

A Saudi official told news agency the decision to close the area was "unprecedented".

On Wednesday, Saudi Arabia suspended the umrah for its own citizens and residents over fears of the coronavirus spreading to Islam's holiest cities.

The move came after authorities last week suspended visas for the umrah and barred citizens from the six-nation Gulf Cooperation Council from entering Mecca and Medina.

Saudi Arabia on Thursday declared three new coronavirus cases, bringing the total number of reported infections to five.

The umrah, which refers to the Islamic pilgrimage to Mecca that can be undertaken at any time of year, attracts millions of Muslims from across the globe annually.

The decision to suspend the umrah mirrors a precautionary approach across the Gulf to cancel mass gatherings from concerts to sporting events.

It comes ahead of the holy fasting month of Ramadan starting in late April, which is a favoured period for pilgrimage.

It is unclear how the coronavirus will affect the hajj, due to start in late July.

Some 2.5 million faithful travelled to Saudi Arabia from across the world in 2019 to take part in the hajj, which is one of the five pillars of Islam as Muslim obligations are known.

The event is a massive logistical challenge for Saudi authorities, with colossal crowds cramming into relatively small holy sites, making attendees vulnerable to contagion.

Already reeling from slumping oil prices, the kingdom risks losing billions of dollars annually from religious tourism as it tightens access to the sites.