It’s Not Whether You Were Exposed to the Virus. It’s How Much. - The New York Times

When experts recommend wearing masks, staying at least six feet away from others, washing your hands frequently and avoiding crowded spaces, what they’re really saying is: Try to minimize the amount of virus you encounter?

Scientists are studying ferrets, hamsters and mice for clues but, of course, it wouldn’t be ethical for scientists to expose people to different doses of the coronavirus, as they do with milder cold viruses.

“I don’t think we can make anything better than an educated guess.”.

The new coronavirus, SARS-CoV-2, is more similar to the SARS virus and, therefore, the infectious dose may be hundreds of particles, Dr.

But in the case of the new coronavirus, people who have no symptoms seem to have viral loads — that is, the amount of virus in their bodies — just as high as those who are seriously ill, according to some studies.

And coronavirus patients are most infectious two to three days before symptoms begin, less so after the illness really hits.

People may take in virus by touching a contaminated surface and then putting their hands on their nose or mouth.

Coughing, sneezing, singing, talking and even heavy breathing can result in the expulsion of thousands of large and small respiratory droplets carrying the virus.

Larger droplets are heavy and float down quickly — unless there’s a breeze or an air-conditioning blast — and can’t penetrate surgical masks.

A number of studies of flu, rhinovirus, coronavirus and other microbes have shown that respiratory illnesses, including the new coronavirus, can spread by touching contaminated surfaces, particularly in places like day care centers, offices and hospitals.

The best way to protect yourself from coronavirus — whether it’s surface transmission or close human contact — is still social distancing, washing your hands, not touching your face and wearing masks.

has recommended that all Americans wear cloth masks if they go out in public.

This is a shift in federal guidance reflecting new concerns that the coronavirus is being spread by infected people who have no symptoms.

Until now, the C.D.C., like the W.H.O., has advised that ordinary people don’t need to wear masks unless they are sick and coughing.

Masks don’t replace hand washing and social distancing.

If you’ve been exposed to the coronavirus or think you have, and have a fever or symptoms like a cough or difficulty breathing, call a doctor.

If you’re sick and you think you’ve been exposed to the new coronavirus, the C.D.C.

But they noted that aerosols, because they are smaller than 5 microns, would also contain much less, perhaps millions-fold less, virus than droplets of 500 microns.

Apart from avoiding crowded indoor spaces, the most effective thing people can do is wear masks, all of the experts said

Even if masks don’t fully shield you from droplets loaded with virus, they can cut down the amount you receive, and perhaps bring it below the infectious dose