Ask Well: Do Face Masks Really Keep You Healthy?



Q. How effective are antimicrobial “courtesy masks” at preventing the spread of contagious airborne illnesses?

A. The best evidence suggests that, when sick, wearing a mask can help to protect others from getting sick. And when well, wearing a mask around those who are sick will probably decrease your own chances of becoming infected. But the masks are far from foolproof.

Courtesy masks, or what we doctors refer to as surgical masks, were introduced into the operating room in the late 1800s. They quickly became popular among a public eager to protect itself against the influenza pandemic of 1918.

A century later, the advent of modern molecular techniques confirmed that surgical masks can indeed provide good protection against flu. In a 2013 study, researchers counted the number of virus particles in the air around patients with flu. They found that surgical masks decreased the exhalation of large viral droplets 25-fold. The masks were, however, less effective against the fine viral droplets that can remain suspended in the air longer and are therefore more infectious, cutting them by 2.8 times.

Surgical masks also afford fairly good protection for the worried well. In an oft-cited study of 446 nurses, researchers found surgical masks were as good, or nearly as good, at protecting the wearer against flu as respirators, a somewhat more high-tech, masklike device used in hospitals.

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Vocations: Fighting Disease Is a Battle Often Won With Spreadsheets

Had you originally thought you’d work in a hospital or private practice?

Yes. My father was a gastroenterologist, so between his practice and my medical training, I was only familiar with physicians who worked in clinical practice, did research or trained other physicians.

But during my residency at what is now NYU Langone Health, I started to have doubts. The high volume of patients was exhausting, and the fellowship offered an opportunity to think about whether being a clinician was the right fit.

The officers I’d shadowed during medical school went out into the field to the site of an outbreak, such as a cruise ship, and did what we called shoe leather epidemiology, pounding the pavement.


Dr. Christina Tan meets with colleagues at the New Jersey Department of Health in Trenton.

Bryan Anselm for The New York Times

What else attracted you to this role?

My predecessor was my supervisor during my fellowship.

One minute he was serving as a health expert, and the next he was communicating health risks. Following that, he was responding to a public health emergency or figuring out how to get resources for programs. He had to work with a variety of groups and make decisions really quickly, often with little information.

It was a cool thing to watch and confirmed my interest in this area.

What lessons are there from flu season?

Fortunately, the season has peaked, but we’re still seeing widespread flu activity that will most likely last through May.

The flu is unpredictable, which is why public health departments monitor it all year round.

For example, we saw the emergence of the 2009 H1N1 pandemic in the late spring, after seasonal flu ended that year.

We’ve learned that we need to ensure that public health and health care partners maintain vigilance in monitoring for flu and other emerging infections. We also need to maintain flexibility in our preparedness and response plans so we can adapt what we do, based on what the disease trends tell us.

Do you get out in the field these days?

Yes, but my team mainly plugs away at spreadsheets, looking at data. Most outbreak investigations are not glamorous or hyper-dramatic, like in the movie Contagion.

I’m also the assistant commissioner of the state Epidemiology, Environmental and Occupational Health division.

We often work with local health departments and health care facilities that are in the field interviewing patients and collecting specimens, including blood, sputum and stool, for lab testing, to confirm the presence of certain microorganisms.

Occasionally — particularly with some of the rarer diseases like imported Lassa fever — we’ll work in the field to further monitor hospital staff members that have been exposed, or to interview additional patients.

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Ask Well: Am I Contagious?



Q. Recently, a friend — with a hoarse voice, a cough and a stuffy nose — told me, “Don’t worry. I’m not contagious.” Is she right?

A. It may depend on how long she has been sick. If your friend has a common cold, she will be infectious for about three days after the onset of symptoms. If she has the flu, she will be infectious for about a week.

The best data we have on the infectivity of upper respiratory infections comes from volunteer studies, in which healthy individuals volunteer to be infected with viruses like influenza, the cause of flu, or rhinovirus, the most frequent cause of the common cold. Understandably, the number of such studies is small.

Those studies show that symptoms are an undependable marker of infectivity. A more reliable guide is the natural course of infection, which can be divided into three phases: incubation (infectious without symptoms), symptomatic/infectious, and recovery (noninfectious with symptoms).

The incubation phase lasts about a day for influenza and may be just a few hours for the common cold. During this time, someone can spread infection, but because there are no telltale symptoms, there is little we can do to protect ourselves. We shake hands, spend time together in enclosed spaces, and do all manner of things that unwittingly increase the risk for disease transmission.

During the symptomatic/infectious phase, symptoms like coughing and sneezing serve as a warning sign to avoid direct contact with a sick person, and especially to avoid exposure to respiratory secretions. The symptomatic/infectious phase lasts about five to seven days for flu and about three days for the common cold. Beware, however, that some people, including those who have been vaccinated against the flu, may have only very mild symptoms but can still be contagious.

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