Asymptomatic Patients Accounts for 50% Coronavirus Transmissions, Study Says

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A new study published online in JAMA Network Open says transmission of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from asymptomatic individuals, accounts for about half of all transmissions.

This is also coming as fresh findings show that face masks combined with other preventive measures, such as frequent hand-washing and social distancing, help slow the spread of the coronavirus (SARS-CoV-2) that causes COVID-19.

So why weren’t face masks recommended at the start of the pandemic? At that time, experts didn’t know the extent to which people with COVID-19 could spread the virus before symptoms appeared. Nor was it known that some people have COVID-19 but don’t have any symptoms. Both groups can unknowingly spread the virus to others.

These discoveries led public health groups to do an about-face on face masks. The World Health Organization and the U.S. Centers for Disease Control and Prevention (CDC) now include face masks in their recommendations for slowing the spread of the virus.

The CDC recommends cloth face masks for the public and not the surgical and N95 masks needed by health care providers.

Also called a medical mask, a surgical mask is a loose-fitting disposable mask that protects the wearer’s nose and mouth from contact with droplets, splashes and sprays that may contain germs. A surgical mask also filters out large particles in the air. Surgical masks may protect others by reducing exposure to the saliva and respiratory secretions of the mask wearer.

At this time, the US Food and Drug Administration has not approved any type of surgical mask specifically for protection against the coronavirus, but these masks may provide some protection when N95 masks are not available.

Actually a type of respirator, an N95 mask offers more protection than a surgical mask does because it can filter out both large and small particles when the wearer inhales. As the name indicates, the mask is designed to block 95% of very small particles.

Health care providers must be trained and pass a fit test to confirm a proper seal before using an N95 respirator in the workplace. Like surgical masks, N95 masks are intended to be disposable. However, researchers are testing ways to disinfect N95 masks so they can be reused.

Some N95 masks, and even some cloth masks, have one-way valves that make them easier to breathe through. But because the valve releases unfiltered air when the wearer breathes out, this type of mask doesn’t prevent the wearer from spreading the virus. For this reason, some places have banned them.

A cloth mask is intended to trap droplets that are released when the wearer talks, coughs or sneezes. Asking everyone to wear cloth masks can help reduce the spread of the virus by people who have COVID-19 but don’t realize it.

Cloth face coverings are most likely to reduce the spread of the COVID-19 virus when they are widely used by people in public settings. And countries that required face masks, testing, isolation and social distancing early in the pandemic have successfully slowed the spread of the virus.

While surgical and N95 masks may be in short supply and should be reserved for health care providers, cloth face coverings and masks are easy to find or make, and can be washed and reused.

Masks can be made from common materials, such as sheets made of tightly woven cotton. Instructions are easy to find online. Cloth masks should include multiple layers of fabric. The CDC website even includes directions for no-sew masks made from bandannas and T-shirts.

The CDC recommends that you wear a cloth face mask when you’re around people who don’t live with you and in public settings when social distancing is difficult.

Here are a few pointers for putting on and taking off a cloth mask: Wash or sanitize your hands before and after putting on and taking off your mask; place your mask over your mouth and nose; tie it behind your head or use ear loops and make sure it’s snug; don’t touch your mask while wearing itl if you accidentally touch your mask, wash or sanitize your hands; and if your mask becomes wet or dirty, switch to a clean one. Put the used mask in a sealable bag until you can wash it.

Others include, remove the mask by untying it or lifting off the ear loops without touching the front of the mask or your face; wash your hands immediately after removing your mask; and regularly wash your mask with soap and water by hand or in the washing machine. It’s fine to launder it with other clothes.

Here are a few face mask precautions: Don’t put masks on anyone who has trouble breathing, or is unconscious or otherwise unable to remove the mask without help; don’t put masks on children under 2 years of age; and don’t use face masks as a substitute for social distancing.

The CDC doesn’t recommend using face shields instead of masks because it’s unclear how much protection they provide.

However, wearing a face mask may not be possible in every situation. If you must use a face shield instead of a mask, choose one that wraps around the sides of your face and extends below your chin.

It can be challenging to get used to wearing a face mask. Here are some tips for making the transition: Wear your mask at home for a short time, such as while watching television. Then wear it during a short walk. Slowly increase the time until you feel more comfortable.

Find your fit. If your mask isn’t comfortable or is too difficult to breathe through, consider other options. Masks come in a variety of styles and sizes.

If these tips don’t help or you have concerns about wearing a mask, talk with your health care provider about how to protect yourself and others during the pandemic.

However, Michael A. Johansson, Ph.D., from the US Centers for Disease Control and Prevention in Atlanta, and colleagues examined the proportion of SARS-CoV-2 transmissions in the community that likely occurred from asymptomatic individuals.

The relative amount of transmission was assessed from presymptomatic, never symptomatic, and symptomatic individuals across a range of scenarios.

The baseline assumptions for the model were that peak infectiousness was at the median of symptom onset and that 30 percent of individuals with infection remain asymptomatic and are 75 percent as infectious as those who develop symptoms.

Based on these baseline assumptions, the researchers inferred that about 24 percent of all transmission was accounted for by persons with infection who never developed symptoms. In this base case, 59 percent of all transmission came from asymptomatic individuals: 35 and 24 percent from presymptomatic individuals and individuals who remain asymptomatic, respectively.

At least 50 percent of new SARS-CoV-2 infections were estimated to have originated from exposure to infected, but asymptomatic, individuals under a broad range of values for each of these assumptions.

“These findings suggest that effective control also requires reducing the risk of transmission from people with infection who do not have symptoms”, the authors write. “Multiple measures that effectively address transmission risk in the absence of symptoms are imperative to control SARS-CoV-2.”

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