College of Science

COVID-19: Q&A with two Clemson scientists helps broaden our understanding of the pandemic


Clemson University virologists Kaustubha “Kos” Qanungo and Matt Turnbull.

CLEMSON, South Carolina – Clemson University virologists Kaustubha “Kos” Qanungo and Matt Turnbull have spent much of their careers studying viral diseases in humans, plants and animals.

Qanungo, a lecturer in the College of Science’s department of biological sciences, received his Ph.D. in molecular virology in 2003 from the Indian Institute of Technology in Kharagpur, India. He joined Clemson in 2019.

Turnbull, an associate professor in the department of biological sciences, received his Ph.D. in entomology in 2002 from the University of Kentucky in Lexington. He joined Clemson in 2003.

Given their expertise, both scientists have been following the COVID-19 global outbreak with intense interest. Here are their responses to some commonly asked questions about the pandemic.

What are the signs/symptoms of COVID-19 and when do they occur?

Kos: The most common signs shown by COVID-19 patients are cough – usually a dry cough – and the patient is warm to the touch with a fever. Visible shaking from chills has also been observed. Those who have trouble breathing or are wheezing should seek immediate medical attention.

Symptoms vary among patients. Many individuals who have tested positive were asymptomatic or mildly symptomatic. The most common symptoms have been fever, chills, sore throats, headache, muscle pain, loss of taste or smell, nasal congestion and even diarrhea. The Centers for Disease Control and Prevention (CDC) suggests seeking medical advice if an individual has at least two of these symptoms.

The CDC also suggests calling 911 if a patient has trouble breathing or has persistent pain or pressure in the chest, confusion, inability to wake up or bluish lips or face.

The symptoms appear anywhere between two to 14 days after exposure to the virus. This unusually variable incubation time is what makes the virus so infectious. A completely healthy asymptomatic individual can be a carrier of the virus and potentially infect many people before any signs or symptoms appear. COVID-19 patients usually see a gradual increase of symptoms in the first week. And in the second week, the symptoms usually worsen, with a large number of people requiring hospitalization.

The CDC provides an online COVID 19 self-checker for people who believe they might be experiencing symptoms.

Matt: I’ll point out that anosmia (the loss of smell) has been frequently reported. Also, low oxygen has been reported without the infected people feeling short of breath. With SARS-CoV-2 (the name of the virus that causes COVID-19), different people often show different symptoms. People need to think of the complete set of symptoms, not just one or two. If you’re worried, call (don’t show up in person!) your medical provider.

How infectious is COVID-19?

Kos: The infectivity of a virus is described by its reproduction number or R0 (pronounced R “naught”). R0 defines how many additional individuals can be infected by each infected person during his or her infectious period.

The Los Alamos National Laboratory has published the most recent article in the Journal of Emerging Infectious Disease on April 7. In an article titled “High Contagiousness and Rapid Spread of Severe Acute Respiratory Syndrome Coronavirus 2,” the authors have calculated the R0 of the SARS-CoV-2 virus being 5.7. This means that a single infected person on an average has the potential to infect close to 6 others. This is alarming because during the initial stage of the pandemic, it was thought to be close to 3 – and now it seems to be almost double what we first believed. Here is a look at the infectivity or R0 of some of the other well-known viruses.

  • Seasonal influenza viruses (multiple strains): 0.9 to 2.1.
  • 2009 H1N1 influenza virus: 1.46-1.48.
  • Ebola (2013-2014): 1.51-2.53.
  • Polio (arguably eradicated): 5-7.
  • Smallpox (eradicated): 5-7.
  • Measles: 12-18.

The following two viruses are coronaviruses as well:

  • SARS virus (Severe Acute Respiratory Syndrome Virus), 2002-2003: 0.9-2.1.
  • MERS virus (Middle Eastern Respiratory Syndrome Virus), 2012-2014: approximately 1.0.

The 2019 novel coronavirus causing COVID-19 is many more times infectious than influenza viruses and all other disease causing coronaviruses. It is alarmingly close to the infectivity of the smallpox and polio viruses. The measles virus is the only one mentioned above that is many times more infectious than the SARS-CoV-2.

Matt: The obvious caveat to this question is that if you don’t encounter the virus, it can’t infect you. So, social distancing and hygiene are the only ways to absolutely avoid infection. But Kos is right: SARS-CoV-2 is very contagious – how contagious is still debatable, as we are still learning about the virus. It can be transmitted through the air. It is unclear how long the virus can linger in the air, as most data at this point suggest it is moving via droplets (after being coughed, sneezed, or breathed out); these would not go very far, or last very long in the air. Droplets containing virus might contaminate solid objects (so-called “fomites”), and the virus could maintain viability for hours to days, allowing someone to touch and transmit to a mucosal lining (mouth, nose, eye). Some data additionally suggest SARS-CoV-2 may aerosolize, which would make it possible to remain in the air for a longer duration. This might occur only in specialized circumstances (like during intubation in hospital settings). All of this is why hygiene is so crucial: 20-plus seconds of handwashing with hot water and soap multiple times per day, no touching of the face, daily cleaning of frequently touched surfaces, along with maintaining interpersonal distances (6-plus feet to reduce droplet inhalation). And, of course, use of masks in public, shared spaces, in addition to maintaining distances.

How deadly is COVID-19?

Kos: As per the CDC’s latest National Vital Statistics Report of 2017, a total of 6,515 individuals died from the influenza virus infection in 2017, with a mortality rate of about 0.2%. Unfortunately, the number often reported in the media and social media is around 55,000 deaths with a mortality rate of 2.0%. The majority of the population is getting this data from the CDC, but the fine print is that this number corresponds to “influenza and pneumonia,” not just influenza. Deaths by pneumonia can also be caused by bacteria, fungus and viruses other than influenza. Per the current data, the mortality rate of SARS-CoV-2 is about 2.0-2.7%. From this perspective, it is 10 to 15 times more deadly than seasonal influenza viruses. But there is still plenty of room for argument. This 2% or higher mortality rate is not uniformly distributed across the population. Below are the fatalities, by age, that have thus far been attributed to COVID-19:

  • 80 and older: 14.8%
  • 70-79 years: 8%
  • 60-69: 3.6%
  • 50-59: 1.3%
  • 40-49: 0.4%
  • 10-39: 0.2%

As you can see, the virus has proven to be far deadlier to the elderly and also in individuals with underlying diseases.

It is likely that there could be far more individuals in the population who contracted the virus and never showed any symptoms. This real number will remain elusive until there is a nationwide mass-testing of asymptomatic individuals.

My final thought is that every life matters. As a developed nation, everyone should put aside the political divide and be responsible and compassionate about our seniors. We can’t act irresponsibly by thinking that the virus is no deadlier than flu viruses. It is far deadlier.

Matt: Though it’s too early to know without much more extensive testing, we can still say with certainty that SARS-CoV-2 is much deadlier than the seasonal flu. The case load is not equally spread across everyone, either. Men are much more likely to show COVID-19 symptoms than women. In the U.S., particularly in the South, there is at least some anecdotal evidence that younger cohorts (20 to 40 years old) are more strongly affected than elsewhere. But this is an additional reason for younger persons to be cautious about SARS-CoV-2, beyond avoiding transmission to the community.

There are also very different mortality and critical-case incidences in African American populations, as well as “essential” workers who likely come into more contact with the virus and who are bearing the brunt of COVID-19. Higher incidences among minority populations appear to be due to systemic, socioeconomic reasons rather than anything genetic, reflecting increased occurrences of other environmentally associated diseases in those populations such as cardiovascular and respiratory diseases, stress, diabetes, etc., and higher rates of exposure associated with profession.

It’s also worth recognizing that COVID-19 might exacerbate other conditions. The pandemic is clearly reducing access to medical treatments for diseases such as cancer, or routine services such as childbirth and childhood vaccination, because medical personnel and resources are over-stressed. This can contribute to higher mortality rates, whether directly or indirectly from SARS-CoV-2.

To make matters potentially worse, even if a patient survives, there are suggestions that there could be other long-term health consequences in many cases. Medical bills will surely soar.

It is an understatement to say that an ounce of prevention – social distancing, excellent hygiene – is worth several pounds of treatment.

Does COVID-19 affect adults and children differently?

Kos: As mentioned above, there is a clear age-related correlation. In the U.S., as per data from early April, about 1.7% of the total tested patients were younger than 18 years, while 98% were above the age of 18. There is not much data available for the age group below 10, but probably the infections among this group are pretty low. As of the publication of this article, there have been two infant deaths in the U.S. – one in Connecticut and another in Illinois. Although the number is low in the younger age group, this is still not a reason for this group to take the SARS-CoV-2 lightly. In children with underlying issues like asthma and chronic bronchitis, the SARS-CoV-2 could still prove deadly.

Matt: Kos’s answer is comprehensive.

Can pets and livestock be infected and spread this infection to humans?

Kos: A recent study was published on April 8 in the journal Science titled “Susceptibility of ferrets, cats, dogs, and other domesticated animals to SARS–coronavirus 2” that investigated the effect and susceptibility of several animals to SARS-CoV-2 under laboratory conditions. The overall findings suggested that pigs, chickens and ducks are not susceptible to SARS-CoV-2. Dogs can be infected with SARS-CoV-2 but have low susceptibility. In contrast, cats and ferrets are highly susceptible to the virus, including airborne droplet infection in laboratory conditions. Although there is no report of an animal-to-human transmission from dogs or cats, the study suggests that surveillance of cats for the SARS-CoV-2 might be necessary.

In contrast, another recent paper was published on April 20 in the journal Transboundary and Emerging Diseases titled “Serological survey of SARS‐CoV‐2 for experimental, domestic, companion and wild animals excludes intermediate hosts of 35 different species of animals.” The investigators collected blood samples from a large population of 35 different animals. The study included domestic livestock (pigs, cows, sheep, horses), poultry (chickens, ducks, geese), experimental animals (mice, rats, Guinea pigs, rabbits, monkeys) and companion animals (dogs, cats) and several wild animals. All samples were collected from the animals in their natural wild or domestic environments and none of them showed the presence of SARS-CoV-2. A dog that remained in close contact with a COVID-19 patient also tested negative.

The conclusion from these two studies suggests that dogs can be mildly susceptible and cats highly susceptible to SARS-CoV-2 under laboratory conditions. But in the natural domestic environment, there are only a few sporadic incidences of SARS-CoV-2 infections, with mild to no symptoms in the animals – and in general, not a concern in a healthy household. But it is definitely wise to avoid close contact with a pet if a patient is at home with COVID-19 symptoms. Regardless, the general population is not at risk from infected pets and livestock at this time.

Matt: The line I’ve seen is that pets should practice social distancing, too. Data on animals is highly equivocal, but remain cautious.

May 14 update: A peer-reviewed, controlled study out this week demonstrated cat-to-cat transmission of SARS-CoV-2. While there has been no confirmed transmission of SARS-CoV-2 from cat-to-human, people are urged to keep cats away from confirmed CoV-2 infected individuals.

How severely has South Carolina been affected by COVID-19?

Kos: This question is best answered by a public health professional. From my perspective, South Carolina showed similar trends of the SARS-CoV-2 as the rest of the nation. But a critical observation needs to be emphasized. COVID-19 cases in urban areas have tended to be much higher than in rural areas. We are seeing significantly higher COVID-19 cases in Greenville, Charleston and Lexington counties, with Richland County alarmingly at the top of the chart. This is probably due to the demographic disparity of COVID-19. About 48% of Richland’s population is African American. This is a national trend and concern.

Starting March 28, South Carolina has had 100 or more new cases every day. Among those numbers, the high was 275 on April 16 and the low was 62 on April 20. However, on April 26 it shot back up to 237 and remained over 230 on April 30 and May 2.

In comparison to the rest of the nation, South Carolina has been moderately affected, but the COVID-19 cases in Richland County are comparable to the more severely affected areas of the nation.

Matt: I would argue that the majority of South Carolina has been exceptionally fortunate. Outside of Richland county and the state’s urban areas, caseloads have been low. But as a whole, dense urban areas have been hit harder than rural areas across the state, nation and world. This should make us very cautious about rapidly reopening South Carolina. Social distance – and also geographical distance in rural areas – are probably what has helped keep SARS-CoV-2 cases relatively low in South Carolina.

When will it be safe for South Carolina to return to normal operations?

Kos: I wish I knew the answer. As businesses and public places begin to open up over the next two to three weeks, it will be crucial to see the case number trends. After that, a more realistic prediction can be made. As per modeling projections, South Carolina might see some relaxation in social distancing starting in the middle of June. I am keeping my fingers crossed for a fun and normal July Fourth celebration, but only time will tell.

Matt: One thing seems certain: We’re not going to return to “normal operations” anytime soon. The virus appears to be transmitted primarily by air, so the more we enjoy each other’s company in business and social enterprises, the more the virus is going to enjoy itself – to our detriment. Wearing masks seems to be extremely helpful. Some studies are showing good reduction in expelling virus by sick individuals wearing masks, even if masks are not as helpful in preventing inhalation of the virus. If we want to go back to greater density, we’re going to have to be conscientious about wearing masks and practicing good hygiene.

What we are absolutely missing right now is testing. We don’t have enough information to say that we’ve passed peak COVID-19 in this first phase of the pandemic. Because of this, we must ramp up testing so that we can know when there is an outbreak and to then reduce transmission prior to another full outbreak. Testing has to include asymptomatic individuals to get a better idea of the “hidden” infection load, which is defined as people who might be able to spread the virus without coughing or having a fever.

There has been some discussion of an “immunity passport” – the idea that people who have been previously infected with the virus could return to work and even engage like we’ve done in the past. It is unclear, though, if we will develop an immunity to SARS-CoV-2. Humans do not seem to develop a lasting immunity to the four common cold coronaviruses, while there might be some immunity to the “original” SARS and a related coronavirus, MERS. At this point, there is no evidence that previous exposure to SARS-CoV-2 prevents either contracting or transmitting it again. Thus, from a virology and immunology standpoint, the idea of an “immunity passport” is a legitimate concern. It’s also problematic from ethical and scientific standpoints. Would immunity passports encourage “COVID parties” akin to chickenpox parties, when there’s so much we don’t know about SARS-CoV-2? Are socioeconomically disadvantaged populations likely to feel more obligated to expose themselves in order to get the “immunity passport” than more socioeconomically advantaged individuals?

Are there reasons we should be hopeful in the short run? And the long run?

Kos: If we return to normalcy by the end of the summer, we should be very careful again in the fall when the new flu season is destined to begin. It will be a wise idea to get the flu shot to significantly rule out a potential flu infection. We could again see some alarming case surges in the fall and might have to revert to another lockdown.

As our scientists race toward the production of vaccines and antivirals, there is always hope in the long run. But we are probably in for a long wait and should be careful to comprehend that even a vaccine is not guaranteed to be a magic bullet. It’s possible that a vaccine might not work in the long run. Viruses continuously evolve, and many potential vaccines might not work against an evolved strain, which would create the need for a mixed strain vaccine (similar to the flu vaccine which usually is made up of four circulating strains of the flu viruses). We also still have no clear idea of how long an antibody can last in a COVID-19 patient after remission. These studies are needed to determine whether a potential vaccine needs to be administered just once or yearly like the flu vaccine.

We face a long and convoluted road, but there is always hope and we will eventually see the end of this. History tells us that no pandemic lasts forever, but we have to be careful and be prepared for a potential second and even third wave of the pandemic. We should take the lesson from the 1918 flu pandemic, when the second wave was far deadlier than the first.

Matt: In the short run, I’m not particularly hopeful. Christian Drosten, a leading figure in Germany’s response, refers to the “pandemic paradox” in which the success of our social distancing leads to overconfidence and even distrust among citizens of scientific and medical advice, resulting in a too-quick relaxation of social distancing and isolation. I think we’re arguably seeing this in the U.S., including in South Carolina. It’s important to remember that herd immunity – where enough people are resistant to the virus to prevent it from circulating in a population – generally requires greater than 70% of the population to have immunity. However, the R0 for SARS-CoV-2 probably requires >90% previous experience to generate herd immunity, which we could get to through natural infection or vaccination. As noted, we currently lack evidence that previously infected individuals are immune to subsequent infections. Also, even rosy estimates suggest we’re well below 70% of the population having been infected.

South Carolina’s Department of Health and Environmental Control (DHEC) listed 5,735 individuals as testing positive as of April 28. Even at the most exaggerated infection rate I’ve seen (50 asymptomatic or presymptomatic individuals for every person who tests positive), this suggests that only about 286,000 of South Carolina’s residents have been infected. South Carolina has a total population of 5.1 million, which means that only 6% of our population has been infected by the virus, leaving approximately 4.8 million persons still at risk. We have a long way to go to before we reach herd immunity. And because we still don’t really know the full range of symptoms, we certainly don’t know the long-term consequences of COVID-19.

We are woefully undertesting! Recent estimates are that South Carolina is about 425 tests per day short of where the state should be when we reopen. Lacking these tests, we really don’t know how much SARS-CoV-2 is out there. Since the virus can be transmitted by people not showing symptoms, we need to be testing asymptomatic persons to determine what the incidence is – and we’re nowhere near that.

Wearing a mask seems likely to help a lot. Maintaining some form of social distancing (no in-person sporting events, reduced density in classrooms, as examples) should assist in pegging the virus back. While not yet known for sure, there’s some suggestion that warmer weather and humidity will help, so that will hopefully reduce incidences during the summer. All of these are likely to reduce the effective R0 of the virus, reducing its ability to persist in the population. Conversely, relaxation of them means it’s likely to re-establish. This means we’re very likely to see resurgences (plural) of the virus. One concern I have is a lack of a coordinated, standardized plan across municipalities. The long presymptomatic or asymptomatic incubation period means that an outbreak in one place will easily seed a neighboring vicinity. Municipalities that decide to relax social distancing will probably negatively impact adjacent areas.

In the long term, I’m more positive. There’s a massive coordinated push for vaccine and therapeutic development and testing. A number of items that are already approved, such as oral polio, BCG vaccines and Remdesivir, or that have gone through phase one or phase two trials, could rapidly scale up. Remdesivir, in particular, shows some minor positive therapeutic ability. I’m pretty bullish about the incredible rate at which vaccine development is proceeding. We seem likely to have multiple vaccines in testing by the end of the year, and governments and NGOs seem committed to parallel testing of vaccines, which increases the probability of getting one or more effective vaccines into use.

Finally, there has been little evidence to this point that the virus is evolving in “meaningful” ways that might render a vaccine less effective. This is a fantastic observation.

Editor’s note:

As the COVID-19 pandemic continues to evolve, we will post periodic updates to existing questions or to new ones.

Here is an update to a new question that was posted on May 14, 2020.

There are reports that some children have developed rare but potentially dangerous complications thought to be linked to the coronavirus. What can you tell us about this?

Matt: Yes, this is scary – anything involving children will be. But it’s extremely important to state two things first: It remains unclear how susceptible children are to SARS-CoV-2. We don’t know infection rates because we aren’t testing enough, and we don’t know how often an infection causes symptoms in children. Secondly, we need to recognize that observations of the “rare but potentially dangerous complications” are still new, which means we lack good data. In other words, we need to be cautious in looking for patterns when the picture is unclear. We want to be aware and attentive, without panicking, and look for those patterns that arise consistently over time, not with a single or few instances.

What we are beginning to understand is that some children are showing the respiratory responses that we think of with COVID-19, while others are showing what’s been termed Pediatric Multisystem Inflammatory Syndrome (PMIS). Reported cases of COVID-19 in children  remain rare. Serious, life-threatening cases of COVID-19 appear mostly in children with previously diagnosed serious medical conditions, as reported this week in JAMA Pediatrics. But PMIS is likely scarier for people. The initial thought is that some children might be responding to a CoV-2 infection that’s been beaten off by generating an out-of-control immune response (the inflammation part) that attacks their own bodies in a multisystem fashion – particularly the cardiovascular system. This results in reduced blood flow and pressure, which in turn can cause problems with numerous body systems. Symptoms include swollen lymph glands, rash, fever, reddish eyes and abdominal pain. They do not include shortness of breath or coughing.

It’s very important that parents should contact their pediatricians if their children of any age – from infant through teen – show PMIS symptoms. To this point, treatment outcomes seem mostly positive if they’re started early in presentation.

Finally, this is yet another good reason to keep up social distancing, wear masks and reinforce the need for excellent hygiene. Observations of these severe complications associated with CoV-2 infection in children, lack of clarity about long-term consequences of these infections, and the potential to transmit the virus to others are all worrisome. Play dates, visits to common playgrounds, etc., should still be severely limited.

Kos: Although COVID-19 morbidity and mortality in children remains low, a new concern is developing. The journal Hospital Pediatrics reported on April 7 that a 6-month-old infant who was positive with COVID-19 was admitted to the Palo Alto Medical Foundation in California with classic symptoms of Kawasaki disease (KD). This disease causes inflammation of the walls of blood vessels in the body and can also affect other organs. Lately, more and more reports of the typical and atypical Kawasaki-like diseases in children have been reported. Some of these symptoms are similar to toxic shock syndrome caused by bacterial toxins that make our immune system become over-reactive. We already know that SARS-CoV-2 is capable of over-activating the immune system, which is one of the leading causes of mortality in adults.

Interestingly, there are reports of inflammatory disease in children associated with several viruses and even with a strain of a SARS coronavirus published in the Journal of Infectious Diseases in 2005. Over the years, there have also been sporadic reports of the association of Kawasaki disease with other strains of coronaviruses. But as Matt said, the data is still insufficient to conclude a positive association of the inflammatory disease in children with SARS-CoV-2.

This becomes even more complicated because we don’t know the exact details of the underlying cause of the Kawasaki disease other than that it is caused by an over-reactive immune system. Hence, there is no specific test or diagnostics. Physicians have to rely entirely on observation, and you can well imagine that this can be a real challenge for parents as well. It can often be difficult to tell the difference between a fussy infant and one who is truly ill.

Fortunately, the inflammatory disease is not a universal concern with every young individual who contracts SARS-CoV-2, and it is usually treatable with aspirin and immunoglobulins (antibodies).

There is another report that SARS-CoV-2 is unmasking a disease called Brugada syndrome, which was first described in the 1990s. This is a genetic disorder prevalent among Southeast Asian men that can lead to cardiac arrhythmia and sudden cardiac arrest. This underlying condition is often silent and remains undiagnosed. Clinicians treating COVID-19 patients first reported this in a 49-year-old man from Bangladesh on March 25 in the Heart Rhythm Journal. Alarmingly, an 8-year-old child in New York City suddenly went into a cardiac arrest but luckily was revived by his 15-year-old brother who performed CPR. The father reported that his child had had a fever and diarrhea for about three days but had tested negative for SARS-CoV-2. But when the child was hospitalized after the cardiac arrest, the antibody test came back as positive for SARS-CoV-2. This remains a mystery, and I am sure new insights will be revealed in the coming days.

No matter what, all parents need to be very careful with their young ones and should be on the lookout for any unnatural behavioral discomfort, while also practicing the preventive measures mentioned above by Matt. This novel virus is unfolding new cases, observations and findings on a daily basis, and we are still in the middle of a pandemic that it is far from over.

Here is a new question that was posted on May 26, 2020:

What is the deal on wearing masks? Are some masks better than others? Do they protect the wearer or just those in proximity to the wearer?

Matt: Short answer: Wear a mask. Doing this helps your community, and not just because it helps you. By wearing a mask, you’ll reduce virus spread. Any sort of cloth material that blocks light and is worn over your mouth and nose should be sufficient to reduce the spread of the virus. Remember to not fidget with or touch your mask because your hands might have virus on them.

The longer answer is there are two reasons to wear masks: 1) to protect the wearer; 2) to protect bystanders. Both purposes are addressed effectively by wearing masks, but different types of masks address these purposes in different ways. Medical personnel who are at greatest risk of encountering very small particles of viruses (aerosolized virus) and also the highest doses of virus need the specialized N95 masks to prevent inhalation of the virus. Since the general population does not typically encounter these smallest infectious particles or such extremely high doses of virus, the general population does not need N95 masks.

On the other hand, anything that catches liquid droplets released by the mouth or nose of an individual can potentially reduce spread of the majority of the virus. A cloth mask with a layer of cloth that is thick enough and with a tight enough weave to not allow light to pass through it is sufficient for this purpose. Data suggest that the CoV-2 infection rate and the severity of COVID-19 symptoms are related to the initial dose. By wearing masks, the general population can reduce potential transmission rates to individuals around them, and then limit the infectious dose a bystander might encounter.

Given the above, people should most definitely wear masks whenever in public. This is a community issue, not a personal one. There is limited evidence that wearing a mask or face covering will prevent someone from inhaling the virus and becoming infected. But there is strong evidence that wearing a mask can reduce the chance that someone infects another person.

So, care about your community and wear a mask!

Perhaps most importantly, wearing a mask is not a replacement for social distancing. Reducing personal interactions by keeping interpersonal distance (first by not traveling, second by not being in a crowd) is the surest way to avoid getting infected and/or spreading the virus. If you have to be in public, wear a mask. But wearing the mask is not a preventative, only a reductive prophylactic. What this means is, as we begin opening up businesses and trying to go about our day working, shopping, or seeking entertainment, people should wear masks but always maintain space, as well.

Also, data suggest that infected individuals have peak virus shedding from their respiratory system before they show symptoms. This is different from the flu, for example, where infectivity correlates with feeling poorly – the sicker you feel, the more infectious you usually are. With CoV-2, you can feel perfectly fine but still have a raging infection that is spread every time you speak (or run, or sing in choir, etc.). Everyone’s mantra for the duration of this pandemic should be to act as if you are infected and take appropriate precautions. Again, this means social distancing and, if in public, mask-wearing.

Finally, there has been some confusion due to early requests by the Surgeon General and CDC to not use masks. These statements were specifically meant to address shortages of N95, allowing medical/front-line personnel to get enough. At this point, the medical community has fully gotten behind the advice for the general public to wear masks when in public.

Kos: I will comment on some of the technical aspects of the respiratory droplets, how they are classified, their ability to carry pathogens or viruses like SARS-CoV-2, and finally correlate them with the mask type, material, and the consequences of wearing a mask.

Respiratory droplets are naturally generated as we breathe, vocalize, eat, cough, sneeze, or yawn. They can be generated through the nose regardless of whether your mouth is open or closed. But there is an extensive classification of these droplets based on their dimension that is routinely used in many ways and many places. For example, they are used to classify the mode of transmission of the pathogens (like the SARS-CoV-2 in this context) in microbiology, infectious disease and epidemiology. In health care settings, they are used to assess the risk of these droplets being generated from a simple patient visit, in a surgery or any intubation process through mouth or nose. They are used in rating air handling systems and designs. And even your house or vacuum cleaner filters are rated for the droplet transmission at an industry standard.

What is in the dimension of these droplets? The first one is referred to as “droplets” that are usually larger than 5 microns or micrometers (1/200th of a millimeter). They are routinely generated as we speak, sing, exercise with open mouth, eat, cough, sneeze, yawn – almost every time we open our mouths. These “droplets” are the vehicles for the SARS-CoV-2 transmission. Fortunately, these larger “droplets” (although very small and invisible to the naked eye) are pulled down by gravity fairly quickly. Hence, the now-familiar “6 feet of distancing” is recommended as a preventive measure for the COVID-19. Usually, these “droplets” will fall to the ground around the person who is generating them within 3-4 feet or about 1 meter (Who Publication: Natural Ventilation for Infection Control in Health-Care Settings).

When inhaled, these “droplets” are usually (this doesn’t mean 100%) trapped in our noses and aren’t able to enter the respiratory tract. In this context, a simple folded up cloth can be very effective to add a preventive layer on your mouth and nose. The general public does not need an N95 mask. A simple cloth mask is effective enough and can be extremely helpful in adding an extra layer of protection. It is not 100% effective in an experimental situation, but it should not be a concern for the general public whether a cloth will allow a 5-micron droplet to pass. For all practical purposes, a mask or cloth over the face is a highly effective way to reduce the SARS-CoV-2 transmission if you are out in a public place.

The last thing is a little out of context but worth mentioning. Another kind of droplet, called a “droplet nucleus,” is more often 1-2 microns in size. These “droplet nuclei” are generated with every breath that we exhale all the time. Unlike “droplets” being predominantly generated by mouth, “droplet nuclei” are constantly being generated through the nose in addition to the mouth. We are fortunate that the coronaviruses are relatively heavy with a large genome and can’t be carried through the “droplet nuclei.” Otherwise, this pandemic would have already been devastating on an unimaginable scale. These much smaller “droplet nuclei” are not immediately pulled to the ground by gravity and can hang in the air for hours and travel hundreds of feet on currents of air. Even the simple movement of people can generate sufficient air current to transport these “droplet nuclei” relatively long distances. Interestingly, we talked earlier about the highly infectious measles viruses. The measles viruses – with approximately half the genome size of the coronaviruses – can be carried by “droplet nuclei.” This is the reason the measles virus – unlike the coronaviruses – can be transmitted hundreds of feet through the air. An ordinary cloth mask – as opposed to an N95 – would offer almost no protection from the pathogens carried via “droplet nuclei.”

As we are all fighting the pandemic and sometimes feeling frustrated and hopeless, we should at least feel grateful that a virus as deadly as SARS-CoV-2 isn’t able to be transmitted via “droplet nuclei.” We are lucky that we don’t require an N95 mask and that cloth or cloth masks can prevent the coronavirus. We should take full advantage of this by wearing cloth masks in all public places.

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