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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.

Udupi, June 2: The number of positive cases may continue to be more in Udupi district since the results of more than 3,000 samples are pending with Labs.

The district total cases to 260. The figure had seemed far-fetched on May 15, when the number of cases stood at just three. The latest spike has been attributed to the return of migrants from other States as well as from abroad. These samples are from people who returned to the district in the last two weeks.

This delay is because the laboratories testing samples from Udupi are burdened with a high case-load after more than 8,500 people returned to the district, particularly from the neighbouring state of Maharashtra.

"Samples have piled up after the influx of people returning from other states and from abroad," says Dr Prashant Bhat, nodal officer for COVID-19 in Udupi. This delay has caused returnees in institutional quarantine to stay on for as long as 18 days.

The designated laboratory for coronavirus testing in Udupi is Wenlock District Hospital in Mangaluru. The district administration also sends samples to laboratories at the Kasturba Hospital in Manipal, Yenepoya Medical College, Mangaluru, KS Hegde Medical Academy, Mangaluru, and Viral Diagnostic Laboratory in Shivamogga. Apart from Udupi, the laboratory in Manipal is also testing samples from Uttara Kannada district. The laboratory in Shivamogga is also testing samples from Shivamogga and Bijapur districts. The laboratories in Mangaluru, similarly, have samples from Dakshina Kannada district.

Dr Avinash Shetty, Medical Superintendent of Kasturba Hospital in Manipal, one of the private laboratories being used by the Udupi district administration, said that they are testing samples in batches. "We received around 600 samples today and we will be testing them now. The backlog of samples should be cleared in the next few days," Dr Avinash said.

All 73 cases reported in Udupi on Monday were patients with travel history of returning from Maharashtra or patients with travel history of returning from abroad.

In cases of some patients who tested coronavirus positive in the past week, people were released from institutional quarantine after a stipulated period only to be tracked down again and admitted in hospitals after their results returned positive.

While two such cases emerged in Belapu and Belman in the district, the administration is now following up with others who were released from institutional quarantine to ensure they remain in home quarantine till their test results are confirmed.

The spike in cases among returning migrants in Udupi also comes at a time the Karnataka government reduced restrictions on interstate travel.

Mangaluru, Mar 28: After a youth from Dakshina Kannada who tested positive for the deadly Covid-19 revealed that he had travelled by a bus, authorities have requested all his fellow passengers to visit their nearest district hospital. 

The 21-year-old man hailing from Belthangady taluk had flown from Dubai to Bengaluru on March 21 and on the same day travelled to Mangaluru by the KSRTC bus bearing registration number KA 19, F3329. 

As he was suffering from fever and cough he was admitted to Puttur government hospital on March 24. He was tested positive for the novel coronavirus on March 27.   

It is not yet know how many passengers were there on board the above mentioned bus which had departed Bengaluru at 4:30 p.m. on March 21. It is believed that most of the passengers who travelled by this bus are residents of Dakshina Kannada. 

Hence, the KSRTC authorities today requested all the passengers who travelled by this bus to visit their nearest district hospital for necessary checkup. The passengers also were urged to quarantine themselves for next couple of weeks.