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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.

Follow latest updates on the Covid-19 pandemic here

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.

Bhopal, Jul 25: Madhya Pradesh chief minister Shivraj Singh Chouhan said on Saturday he has tested positive for the coronavirus disease (Covid-19).

Chouhan made the announcement in a series of tweets.

“My dear countrymen, I had symptoms of COVID-19 and after the test, my report has come back positive. I appeal to all my colleagues that whoever came in contact with me, must get their corona test done. And my close contacts should quarantine themselves,” Chouhan said in a tweet in Hindi.

“If COVID19 is treated on time, a person is completely cured. I have been reviewing the status of corona infection every evening since March 25. I will try to review corona situation through video conferencing as much as possible now,” he added.

The chief minister said the review meeting will now be held by home minister Narottam Mishra, urban development and administration minister Bhuppendra Singh, health education minister Vishvas Sarang and health minister Dr Prabhuram Choudhary in his absence.

“I will also continue to do everything possible to help control COVID19 in the state during treatment,” he said.

One of Chouhan’s ministerial colleagues tested positive for Covid-19 late on July 22.

The chief minister along with the minister, the Bharatiya Janata Party’s state unit president VD Sharma and state unit general secretary (organisation) Suhas Bhagat had visited Lucknow in a government plane on July 21 to attend the funeral of MP governor Lalji Tandon who died away in the Uttar Pradesh capital, his hometown. during hospitalisation.

The minister is admitted to a private medical college’s teaching hospital in Bhopal.

New Delhi, Apr 9: Kerala opposition coalition United Democratic Front on Thursday submitted a roadmap to Prime Minister Narendra Modi for staggered lifting of ongoing lockdown due to COVID-19 pandemic.

The coalition led by leader of opposition Ramesh Chennithala has given a set of recommendations to Modi in this regard, which include those made by an expert committee headed by deputy leader of opposition M K Muneer.

The committee was set up to suggest measures to be taken by the government for smooth transition from lockdown to normalcy.

It listed an eight-point exit strategy for removing lockdown in a staggered approach at a district level, with emphasis on hotspots to avoid further spread of virus and ensure smooth restart of economy.

This approach is tuned to the unique needs of each district and all the districts should also be categorised as per their risk levels, the report said.

The report has also been submitted to chief ministers of all states, former prime minister Manmohan Singh, Congress president Sonia Gandhi, senior Congress leader Rahul Gandhi among others.

The committee recommended that COVID-19 rapid testing must be enhanced across the country and the testing target be widened to 500 tests per one lakh population.

"A step-by-step approach is necessary for each sector along with conditions that need to be considered for each sector," the report said.

"There is a need for a comprehensive economic stimulus package in addition to the ones already announced after considering all the industries," it added.