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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.

Thiruvananthapuram, Apr 22: Eleven more people tested positive for COVID-19 in Kerala with totalpositive cases in the State touching 437on Wednesday.

Two house surgeonsof the Kozhikode Medical college are among those who have tested positive for the virus.

The two had travelled outside the state,Chief Minister Pinarayi Vijayan told reporters.

Kannur reported seven cases, Kozhikode two, while one case each was reported from the districts of Kottayam and Malappuram.

Only one person tested negative.

The state has 127 active cases and 29,000 people are under observation, including 346 in hospitals.

New Delhi, Jan 31: Substantial competition and low tariff rates by telecom operators since 2016 have led to a financial stress in the sector, the Economic Survey said on Friday.

The data price in the country came down by over 99 per cent during 2016-2019, making it among the lowest tariff in the world, according to the survey.

"Since 2016, the sector has witnessed substantial competition and price cutting by the telecom service providers (TSPs), creating financial stress in the sector. As a result, the sector is experiencing consolidation. While some operators have filed for bankruptcy, others have merged, in their quest to improve viability," the survey report said.

In April-June 2019, the price of data was Rs 7.7 per gigabyte (GB) as compared to Rs 200 per GB in June 2016, it added.

"The Average Revenue Per User (ARPU) for GSM based mobile services has also gone down substantially from Rs 126 in June 2016 to Rs 74.30 in June 2019," the survey said.

The tariff war started in the market with entry of new telecom operator Reliance Jio in September 2016.

"BSNL and MTNL are also affected by the tariff war that has impacted their cash flow resulting in mounting losses," the survey said.

The financial health of the public sector telecom firms plummeted to a level where they have been finding hard to pay employees salaries in time.

The government has drawn up a plan to revive these PSUs which is still in works.

The revival plan consists of several measures, including reduction of staff cost through voluntary retirement scheme, allotment of spectrum for 4G services, monetisation of land and building, tower and fibre assets of BSNL and MTNL, debt restructuring through sovereign guarantee bonds and ''in-principle'' approval for merger of BSNL and MTNL.

The survey said that the wireless telephony now constitutes 98.27 per cent of all subscriptions whereas share of landline telephones now stands at only 1.73 per cent where market share is dominated by private sector players.

"The overall tele-density in India stands at 90.45 per cent, the rural tele-density being 57.35 per cent and urban teledensity being 160.71 per cent at the end of September 2019. The private sector dominates with a share of 88.81 per cent (106.06 crore connections) at the end of September, 2019 while the share of public sector was 11.19 per cent (13.36 crore connections)," the survey said.

The lower price of data has also lead in surge of broadband connections and average consumption of the internet.

Total broadband connections increased by about ten times, from 6.1 crore in 2014 to 59.46 crore in June 2019, the survey said.

The number of internet subscribers (both broadband and narrowband put together) stood at 66.53 crore at the end of June 2019 as compared to 25.16 crore in 2014.

The number of mobile internet subscribers was 64.36 lakh at the end of June 2019 while the number of wireline internet subscribers was 2.17 crore.

"India is now the global leader in monthly data consumption, with average consumption per subscriber per month increasing 157 times from 62 MB in 2014 to 9.8 GB in June 2019. The cost of data has also reduced substantially, enabling affordable internet access for millions of citizens," the survey said.