Infectious Respiratory Disease

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What is an infectious respiratory disease?

Infectious respiratory diseases are diseases caused by viruses, bacteria, and other pathogens that affect the respiratory system and are mostly spread from person to person. According to the US Center for Disease Control (CDC),  “Every year, respiratory viruses such as influenza (flu), SARS-CoV-2, and respiratory syncytial virus (RSV) cause hundreds of thousands of hospitalizations and thousands of deaths during the fall and winter virus season.”¹ Symptoms may include fever, chills, fatigue, cough, runny/stuffy nose, decrease in appetite, sore throat, vomiting, new loss of taste or smell, headache, diarrhea, or weakness. Some populations, like the old, the young, and those with certain conditions that compromise their immune system are at an increased risk.

“Respiratory viruses spread via three different transmission routes: contact (direct or indirect), droplet and aerosol transmission. Contact transmission refers to direct virus transfer from an infected person to a susceptible individual (e.g. via contaminated hands) or indirect virus transfer via intermediate objects (fomites). Transmission of virus through the air can occur via droplets or aerosols. …. Droplets generated during coughing, sneezing or talking do not remain suspended in air and travel less than 1 m before settling on the mucosa of close contacts or environmental surfaces. Aerosols have a slow settling velocity, thus they remain suspended in the air longer and can travel further.”² We attempt to stop, or at least slow, this transmission through methods such as vaccines, wearing a face mask, social distancing, quarantining, more frequent hand washing, and increased cleaning of surfaces.

History and evolution of masks as a means of preventing the spread of infectious respiratory disease

Medical masks as we think of them today can be traced back to 1867 when “the British surgeon Joseph Lister postulated that wound disease was caused by the germs of the microscopically small living entities that Louis Pasteur had recently described. Lister suggested eliminating germs through the use of antiseptic substances. But in the 1880s, a new generation of surgeons devised the strategy of asepsis that aimed to stop germs from entering wounds in the first place.”³ Prior to that time, masks were sometimes used but often just as a way of shielding medical personnel from noxious odors.

During the Manchurian plague of 1910-11 and the influenza pandemic of 1918-19, the use of masks extended beyond the operating room and were worn by healthcare workers and even members of the general public to protect the wearer from exposure to disease. Some cities, like San Francisco even implemented mandatory mask wearing policies. Throughout the 1960s, masks were increasingly made from synthetic materials that provided more protection for the wearer, but broke down in the sterilization process and so were thrown away after use. These disposable masks cut down on cost and labor and became increasingly popular and eventually the standard in hospitals and other medical facilities.⁴

During the 2020 COVID-19 pandemic, people were required to wear masks in public that covered their mouth and nose. A variety of masks were used including disposable surgical masks, N95 respirators, homemade masks, and store bought cloth masks. These vary greatly in their effectiveness.

How do masks really work?

While we often think of a face mask like a sieve, blocking out particles that are too large to pass through a particular hole, it is a bit more complicated than that. Masks are made from cloth (synthetic or natural) that is made up of woven fibers. These fibers create an intricate web and a tortuous path that a pathogen must pass through in order to penetrate to the other side. Larger particles either get stuck on the outside or along the way through in a process called inertial deposition. Very tiny particles tend to migrate to the fibers on their way through the mask and become attached in a process called diffusion. Pathogens and other particles that are between these two extremes have the highest chance of making it through although many of them will be stopped along the way.⁵

Masks work in two ways. They provide protection to the wearer and keep the wearer from passing along pathogens they may carry. Wearing a mask effectively blocks a large portion of viruses exhaled from breathing, talking, coughing, and even sneezing. Some side leakage will occur, but the overall amount is greatly reduced. For a healthy person, wearing a mask decreases their chance of being infected, especially in a high risk environment.⁶

What does the data say? Do masks work?

The short answer is yes. Masks work to slow, and sometimes stop, the spread of infectious respiratory diseases. However, just how well masks work depends on the type of mask worn and which disease you are attempting to prevent. The increased wearing of masks during flu season in 2020 and 2021 contributed to a staggering drop in the numbers of influenza cases those years. While masks did work to slow the spread of COVID-19, it did not do it as effectively as it did influenza during the same time period.

“[M]asks prevent infected persons from exposing others to SARS-CoV-2 by blocking exhalation of virus-containing droplets into the air (termed source control). This aspect of mask wearing is especially important because it is estimated that at least 50% or more of transmissions are from persons who never develop symptoms or those who are in the presymptomatic phase of COVID-19 illness. In recent laboratory experiments, multilayer cloth masks were more effective than single-layer masks, blocking as much as 50% to 70% of exhaled small droplets and particles.”⁷

It is important to consider that masks are very effective as part of combatting the spread of a respiratory disease throughout a population. While some may offer personal anecdotes of still getting infected with a mask or not getting infected without one, the data as an entirety cannot be ignored. Requiring the population to wear masks is not about protecting the individual, but society as a whole. In particular, healthy individuals with a robust immune system may not feel the need to wear a mask as getting something like the seasonal flu or COVID-19 are not likely to be serious for them. However, wearing a mask could keep them from unknowingly spreading an infection to someone for whom it could be much more serious. 

A large study in Bangladesh showed that increasing the proper use of face masks by 29 percentage points reduced the amount of verified symptomatic cases by 11.1%. ⁸ One of the things that really struck me about this study was the ways in which they adjusted for factors like implementation of other preventative measures, age, and risk factors. Numbers were given not only for overall results, but for variations of factors. This is exactly the type of conversation I am encouraging with my students.

Is there a negative side to wearing a mask?

Many people were hesitant or outright refused to wear a face mask during the COVID-19 pandemic. Their reasons for not wearing one were personal, physical, physiological, or even political. Some individuals reported discomfort or that they felt they could not breath as well. However, there is no significant reduction in respiratory function in healthy individuals or even those with asthma from the proper use of a surgical mask.⁹ This feeling could increase anxiety in some. People that rely on lip reading or even facial expressions for context in communication were limited in their ability to understand others. Some felt that their connection to others was impacted by the reduced view of the face or that their individual liberties were impacted by the mandated wearing of masks in public in most public places.

What is the conclusion about masks?

While there is certainly variation in mask types and the effectiveness of these types, there is a clear connection between the use of masks and the number of cases of infectious respiratory disease.

How do we know if the data is valid?

Since students will be analyzing and evaluating the data and discussing if it comes from reliable sources, it is important to discuss ways in which data is obtained and how to know if it is indeed valid.

When looking at scientific studies, evaluate the methodology used. There should be a well defined question the researchers are seeking to answer, an explanation of the methods used, and details of how the findings were interpreted. There must be care taken to minimize bias. It is helpful to look at the sample population used. Larger numbers will be more representative of the population as a whole. Also, consider what individuals were included. Is it just one gender or age group? Did they include people with certain health conditions? Depending on the particular study, different population inclusions/exclusions may be appropriate.