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Geneva, May 17: Spraying disinfectant on the streets, as practised in some countries, does not eliminate the new coronavirus and even poses a health risk, the World Health Organization (WHO) warned on Saturday.

In a document on cleaning and disinfecting surfaces as part of the response to the virus, the WHO says spraying can be ineffective. "Spraying or fumigation of outdoor spaces, such as streets or marketplaces, is... not recommended to kill the Covid-19 virus or other pathogens because disinfectant is inactivated by dirt and debris," explains the WHO.

"Even in the absence of organic matter, chemical spraying is unlikely to adequately cover all surfaces for the duration of the required contact time needed to inactivate pathogens." The WHO said that streets and pavements are not considered as "reservoirs of infection" of Covid-19, adding that spraying disinfectants, even outside, can be "dangerous for human health".

The document also stresses that spraying individuals with disinfectants is "not recommended under any circumstances".

"This could be physically and psychologically harmful and would not reduce an infected person's ability to spread the virus through droplets or contact," said the document.

Spraying chlorine or other toxic chemicals on people can cause eye and skin irritation, bronchospasm and gastrointestinal effects, it adds.

The organisation is also warning against the systematic spraying and fumigating of disinfectants on to surfaces in indoor spaces, citing a study that has shown it to be ineffective outside direct spraying areas.

"If disinfectants are to be applied, this should be done with a cloth or wipe that has been soaked in disinfectant," it says.

The SARS-CoV-2 virus, the cause of the pandemic that has killed more than 300,000 people worldwide since its appearance in late December in China, can attach itself to surfaces and objects.

However, no precise information is currently available for the period during which the viruses remain infectious on the various surfaces.

Studies have shown that the virus can stay on several types of surfaces for several days. However, these maximum durations are only theoretical because they are recorded under laboratory conditions and should be "interpreted with caution" in the real-world environment.

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.

New Delhi, Jun 24: Expanding the testing criterion for coronavirus, the Indian Council of Medical Research has said it should be made widely available to all symptomatic individuals across the country.

"Since test, track and treat' is the only way to prevent spread of infection and save lives, it is imperative that testing should be made widely available to all symptomatic individuals in every part of the country and contact tracing mechanisms for containment of infection are further strengthened," it said in an advisory on 'Newer Additional Strategies for COVID-19 Testing' on Tuesday.

In its revised testing strategy for COVID-19 issued on May 18, the Indian Council of Medical Research (ICMR) had advised testing for all symptomatic Influenza-like illness (ILI) among returnees and migrants within seven days of illness.

All hospitalised patients who develop ILI symptoms, symptomatic individuals living within hotspots or containment zones and healthcare and frontline workers involved in containment and mitigation of coronavirus were also advised testing.

The apex health research body has also advised authorities to enable all government and private hospitals, offices and public sector units to perform antibody-based COVID-19 testing for surveillance to help allay fears and anxiety of healthcare workers and office employees.

The earlier advisories on rapid antibody testing advisories had focused on areas reporting clusters (containment zones), large migration gatherings/evacuees centers and testing of symptomatic ILI individuals at facility level.

Besides, the ICMR on Tuesday also recommended deployment of rapid antigen detection tests for COVID-19 in combination with RT-PCR tests in all containment zones, all central and state government medical colleges and government hospitals, all private hospitals approved by the National Accreditation Board for Hospitals and Healthcare (NABH), all NABL-accredited and ICMR approved private labs, for COVID-19 testing.

All hospitals, laboratories and state governments intending to perform the point-of-care antigen tests need to register with ICMR to obtain the login credentials for data entry.

"ICMR advises all state governments, public and private institutions concerned to take required steps to scale up testing for COVID-19 by deploying combination of various tests as advised," the advisory added.