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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.

Using smartphone for long hours every day may do you more harm than you can probably think of. Researchers have found that spending a lot of time with the device and on social media may lead to mental distress and suicidality among adolescents.

The findings, published in the journal CMAJ (Canadian Medical Association Journal) contains guidance for physicians, parents and teachers on how to help teenagers manage smartphone and social media use for a healthy balance between sleep, academic work, social activity, interpersonal relationships and online activity.

"Physicians, teachers and families need to work together with youth to decrease possible harmful effects of smartphones and social media on their relationships, sense of self, sleep, academic performance, and emotional well-being," said lead author of the study Elia Abi-Jaoude from Toronto Western Hospital in Canada.

This review of evidence, led by the Hospital for Sick Children (SickKids), focuses on smartphone use and does not consider online gaming.

"For adolescents today, who have not known a world without social media, digital interactions are the norm, and the potential benefits of online access to productive mental health information -- including media literacy, creativity, self-expression, sense of belonging and civic engagement -- as well as low barriers to resources such as crisis lines and Internet-based talking therapies cannot be discounted," the authors wrote.

The researchers recommend that doctors should ask teenagers to reduce social media use rather than eradicate it completely and encourage parents to be part of the conversations.

Parents should discuss appropriate smartphone use with teenagers to determine together how to reduce risks and set boundaries.

A recent poll from the US indicates that 54 per cent of teenagers think they spend too much time on their smartphones and about half said they were cutting back on usage.

"Encouragingly, youth are increasingly recognising the negative impact of social media on their lives and starting to take steps to mitigate it," the authors wrote.

Boston, Feb 4: Practising yoga may increase levels of a messenger molecule involved in regulating brain activity, and completing one yoga class per week may maintain elevated levels of this chemical, according to a study which may lead to better ways of mitigating depressive symptoms.

The study, published in the Journal of Alternative and Complementary Medicine, assessed a group of 30 clinically depressed patients who were randomly divided into two groups.

According to the researchers, including those from Boston University in the US, both groups engaged in coherent breathing, and Iyengar yoga -- a form of hatha yoga, developed by B. K. S. Iyengar, emphasising on detail, precision, and alignment in the performance of yoga postures.

The only difference between the groups, the scientists said, was the number of 90 minute yoga sessions, and home sessions in which each group participated.

Over three months, they said, the high-dose group (HDG) was assigned three sessions per week, while the low-intensity group (LIG) engaged in two sessions per week.

The participants underwent magnetic resonance imaging (MRI) scans of their brain before the first and after the last yoga session, and also completed a clinical depression scale to monitor their symptoms, the study noted.

Results of the study revealed that both groups had improvement in depressive symptoms after three months.

Their MRI analysis showed that levels of the brain messenger molecule GABA were elevated after three months of yoga, as compared to the levels before starting yoga.

According to the study, this increase was found for approximately four days after the last yoga session, but the rise was no longer observed after about eight days.

"The study suggests that the associated increase in GABA levels after a yoga session are 'time-limited' similar to that of pharmacologic treatments such that completing one session of yoga per week may maintain elevated levels of GABA," explained study co-author Chris Streeter from Boston University.

Providing evidence-based data may help in getting more individuals to try yoga as a strategy for improving their health and well-being, the scientists said.

"A unique strength of this study is that pairing the yoga intervention with brain imaging provides important neurobiological insight as to the 'how' yoga may help to alleviate depression and anxiety," said study co-author Marisa Silveri from Harvard University.

In this study, we found that an important neurochemical, GABA, which is related to mood, anxiety, and sleep, is significantly increased in association with a yoga intervention," Silveri said.