What’s the Safest Way to Shop? Are Certain Blood Types at Higher Risk? Answering Your Questions About COVID-19

The outbreak of COVID-19 has prompted many people to take precautions to keep themselves safe. Dr. Justin Clark, Ph.D., an infectious disease expert, has previously answered a variety of key questions related to the virus for Quantum Nutrition Labs. However, day by day, we are learning more about COVID-19. This has prompted follow-up questions by QNL readers on our blog and Facebook page. We reached out to Dr. Clark to get you the answers you are looking for.  

Editor's note: This article was initially posted during the summer of 2020 and has not been updated to reflect the current scientific discoveries of COVID-19. For more up-to-date information, please refer to the Centers for Disease Control and Protection website. 

This is Part 3 of our COVID-19 series. Please see the other parts below: 

  1. Coronavirus (COVID-19) - What You Should Know
  2. Can Microwaving Mail Kill the Virus? Can You Get COVID-19 Twice? Answering Your Questions about COVID-19
  3. The What We Know Now: The Latest Updates to Your Covid-19 Questions - Q&A with Gabriel Espinoza, Md. What Disinfectants Kill Covid-19? What Is the Progress of a Vaccine? Are Cloth Masks Effective? Are We Experiencing A Second Wave? Are Kids at Risk?

Picture of Dr. ClarkPicture of Dr. Clark

Dr. Clark’s Background:  

Dr. Clark graduated with a B.S. in Biology from the University of North Carolina and was awarded a Ph.D. in Integrative Molecular and Biomedical Sciences from Baylor College of Medicine. He has researched bacterial and viral pathogens for over 10 years. All opinions expressed here are his own.


You can read our previous COVID-19 Q&A with Dr. Clark by clicking here for part one and clicking here for part two.   

QNL: So we know there is that 14-day exposure, but can we truly say we know how long this virus stays in our body? How long are we really contagious for, considering this virus mutates? Which blood types are affected more by this virus? 

Dr. Clark: The 14-day wait time is kind of confusing. That wait period is just to see if you show symptoms after being exposed, because there have only been a handful of cases confirmed where people show symptoms more than 14 days after exposure. If someone shows symptoms, there is a good chance they’ll be contagious for more than 14 days. How long someone is contagious varies a lot if you’re going by how long it takes for a person to test negative for viral RNA after showing symptoms. Earlier reports from China suggested patients shed the virus for an average of 20 days after first detection1 or 8 days after symptoms resolved.2 Another study found that viral RNA became undetectable around 21 days.3 These were all small studies though, and all from China. 

The idea that blood types may affect the outcome of COVID-19 comes from an article that has yet to be peer-reviewed by experts.4 That article looked at the blood types of 2,173 patients in three Chinese hospitals and compared those to the percentages of blood types found in the cities those hospitals were found in. Their data suggested that blood group A was associated with a slight increased risk of infection and death, while O blood groups were associated with a slight decrease in risk. I want to stress that this is just one study and the risk was slight—in some cases, not even statistically significant. 

QNL: Although viral particles can be detected on surfaces for a few days, how long before the viral load falls enough to not cause infection? 

Dr. Clark: This really depends on how many viral particles there are on the surface. For an infectious dose, we really can’t ethically determine what that is for humans. Virologists often work with something called Median Tissue-Culture Infectious Dose, or TCID50. This is, basically, the concentration at which 50% of the cells in a test tube are infected when they are inoculated with a diluted solution of viral fluid.  In the highly cited paper looking at how long SARS-CoV-2 can survive on surfaces, they used roughly 10,000 times the TCID50 and monitored it until it went below the TCID50.5 The tissue-culture infectious dose isn’t the same as a human’s infectious dose, but the half-life determined for TCID50 should be applicable. Researchers determined the half-life for SARS-CoV-2 was 5.6 hours on a steel surface and 6.8 hours on a plastic surface. 

QNL: Based on your knowledge, how long is this pandemic expected to last? Is it true that if the virus is exposed to very hot weather conditions, it may weaken or kill the virus? 

We don’t really know what is going to happen when things warm up. There is some evidence based on the temperature and humidity of where most outbreaks have happened that SARS-CoV-2 could be seasonal.6 Summer tends to slow the spread of most respiratory diseases.7 However, it is hard to say exactly how much the spread will slow. One simple way to think about it in terms of R0 (pronounced R-naught), which is the average number of additional people an infected individual will infect. The R0 isn’t fixed though and many things including social distancing and warm weather tend to bring it down. For the various influenza strains, the R0 is about 1.5.8 This means that every person with the flu will, on average, infect 1.5 others. But during summer months, for a variety of reasons, the R0 of the flu drops below one and the outbreak is unable to continue.  

With SARS-CoV-2, we may not see the R0 drop below 1 during the summer simply because it is much higher than the R0 of the flu (i.e. more easily transmitted). Early estimates generally put SARS-CoV-2’s R0 around 2-3, but some more recent studies have suggested that it may actually be as high as 6 without social distancing.9 

QNL: There were a lot of severe upper respiratory infections going on in January. Could this virus have been in the United States then? Is it possible that some of us have already had the illness? 

It looks like SARS-CoV-2 was starting to spread in the US in January, but it is doubtful that whatever was going around at that time was SARS-CoV-2. For one thing, it takes time for a disease to spread — one case will not become thousands in just a couple of weeks. So, even if SARS-CoV-2 got here in January, the chances of a large percentage of the population being infected before March (at the very least) is low.  

Another reason is that genomic epidemiologists are pretty confident about when the virus arrived in most countries around the world based on the sequencing of the virus genome in different places. They can look at the slight changes in the genome of the virus as it spreads and get a good idea about where it came from. If you look at data from NextStrain, you can see visualizations of this yourself. As far as I know, all sequences to date can be traced back to Wuhan, China or elsewhere in China. If the virus had been circulating widely before we knew about it in Wuhan, we would expect to see a lot more sequences of the virus of unknown or uncertain origin.  

Just to give you a simplified example of how sequences can inform us about a virus’ origin: 

Imagine you have 5 sequences: AAA from day 1 in China, AAG on day 5 from the US, GAA on day 7 from Australia, GGA on day 10 from Canada, and AGG from Europe on day 17. You might conclude that the virus mutated in each country. An example of how the sequence of viral mutations spread is below: 

AAA (China) -> AAG (US) -> AGG (Europe) 

AAA (China) -> GAA (Australia) -> (Canada) 

The full SARS-CoV-2 genome is about 30,000 base pairs long instead of 3, but the principle is the same. 

People walking in streets  wearing  masksPeople walking in streets  wearing  masks

QNL: How is COVID-19 different than the swine flu? 

Dr. Clark: Biologically, swine flu is caused by a virus from a completely different family of viruses (called orthomyxoviridae). Clinically, milder forms of both can look similar, but SARS-CoV-2 is more likely to develop into a severe disease with a case fatality rate that is apparently 10 times that of swine flu. 

QNL: Is there any concern that multiple strains of COVID-19 are circulating? 

Dr. Clark: This is something scientists are keeping an eye on, but to my knowledge there is no indication that clinically distinct strains are circulating. We do know that different lineages of the virus are circulating but there isn’t any evidence that any of them cause a worse form of the disease.  

If you are interested in visualizing the evolution of SARS-CoV-2 as it is spread, NextStrain is a great resource. 

QNL: Can COVID-19 be killed with UV light? How long will viral particles be active on a surface in full sunlight? For example, can it be killed by being exposed to 6 hours full sunlight, at 70 degrees F, on a wood surface like a picnic table? 

Dr. Clark: Since a virus is not a living organism, it is not possible to “kill” it.  However, UV light can inactivate viruses, but the type and strength of UV radiation and the duration needed to inactivate SARS-CoV-2 is unknown right now, so it is probably safer to rely on other methods.  

There is one thing to note about using UV radiation to sterilize potentially contaminated items: the type of UV radiation that works best, UVC, also causes a lot of damage to skin and DNA so other methods are safer in that regard as well. 

It is hard to say how long viral particles can last under conditions like that because UV levels can vary so much with time, weather, and season. But 6 hours of exposure of direct sunlight should inactivate the virus. Even if the UV rays did not do the job, sunlight would heat the picnic table up higher than 70, accelerating inactivation. I would still avoid putting my face on it though! 

QNL: I was tested 14 days ago and just got my results. So is it safe to say that my test results I just got are showing my status as of 14 days ago, not necessarily right now? 

Dr. Clark: This is a good observation. I can’t remember who said it, but one health official said early on that, “test results aren’t giving us a picture of where we are, they are giving us a picture of where we were.” How recent that picture is depends on how quickly tests can be processed. If it is taking 14 days to process tests for everyone in your area, then the numbers are two weeks behind. But the good news is that processing times seem to be less than 14 days in most areas in the US, so the national numbers should not be that far behind. 

Mosquito on a human handMosquito on a human hand

QNL: Can mosquitoes or ticks carry the virus? Can pets transmit COVID-19? 

Dr. Clark: There is no evidence or reason to think that mosquitoes or ticks can carry this virus. There are also no instances of SARS-CoV-2 being transmitted by pets, but there have been a few reports of dogs and cats testing positive without symptoms. I’ll talk more in-depth about this below, but in short: the CDC recommends that, along with practicing good hygiene, you should keep pets indoors and away from strangers and other pets outside the home as much as possible. If someone in your home has COVID-19 or has COVID-19 symptoms, they recommend treating your pet as you would another person—that is to say, limit their interactions as much as possible.  

I know a lot of pet owners are curious about this, so I have summarized what I’ve read about pets and SARS-CoV-2 so far:  

For dogs, it was reported in Hong Kong that 2 out of 17 dogs that came into contact with SARS-CoV-2 patients tested positive, but authorities there stressed that this means infections are infrequent and there is no evidence dogs can pass on the virus. Both of those dogs tested as a “weak positive,” meaning the viral concentrations were low.10  

A recent (mid-April) paper suggested that SARS-CoV-2 may have come from canines.11 Their conclusion is based mostly on the fact that coronaviruses that infect different species tend to cluster with coronaviruses that infect the same species when you look at the number of genetic sites (called CpG sites) that are targeted by antiviral proteins. This isn’t very robust evidence because the clustering isn’t always reliable and because researchers can only look at the clustering of coronaviruses that have been sequenced. If an animal has several coronaviruses with a similar CpG profile, we wouldn’t know this unless these viruses have been sequenced. This is something that should be investigated, but not something I think should be front-page news. 

A study came out this week that looked at the ability of SARS-CoV-2 to replicate in several animal species: cats, dogs, ferrets, pigs, chicken, and ducks.12 Pigs, chickens, and ducks do not seem to be susceptible to the virus. Researchers concluded that dogs were only mildly susceptible because only low amounts of SARS-CoV-2 genetic material have been recovered from 2 of 5 dogs in the study, and only in the rectal swabs. They were unable to recover infectious SARS-CoV-2 particles from any of the other dogs.  

Ferrets and cats, on the other hand, did seem to be susceptible. All infected ferrets tested positive for SARS-CoV-2 particles and showed mild symptoms. Infectious SARS-CoV-2 particles were recovered from nasal, soft palate, and tonsil tissue of the ferrets, but not other tissue including the lungs. Cats appeared to be the most susceptible in this study. Infectious SARS-CoV-2 particles were detected in the upper and lower respiratory tract of the cats in the study, 3 days after being infected. Viral RNA particles were also found in their small intestines. Researchers also put unexposed cats in cages next to infected cats and found that the unexposed cats developed infections, suggesting that cats are susceptible to aerosolized transmission of the viral particles and are able to pass it to one another. 

There are other examples of cats appearing to be susceptible. As of mid-April, there are two reports of domestic cats that tested positive for the virus: one in Hong Kong that did not show symptoms13 and one in Belgium which showed digestive and respiratory symptoms.14 There is also the case of a tiger at the Bronx Zoo that tested positive. Several of their big cats also showed respiratory symptoms.15 

Again, please remember that we do not know if this means pets are able to pass the viral particles on to humans. But the safe and recommended thing to do is to isolate your pets as much as possible if they have been exposed to the virus.

QNL: If you get the virus and have no symptoms, how long will you be infected? After you recover from it, will you now have antibodies to it? 

Dr. Clark: We do not really know. It is probably safe to assume that asymptomatic carriers shed viral particles for as long as symptomatic people, but it is hard to catch and monitor these asymptomatic individuals now. Asymptomatic carriers have been found mostly by accident. Testing or tracking them has not been a priority in places where testing has been sketchy—which is to say, most places.  

Asymptomatic individuals are expected to develop antibodies against the virus. Hopefully, antibody testing will give us a better picture of the prevalence of asymptomatic carriers, but there are concerns about the accuracy of testing until the number of people who test positive is higher than a few percent of the population or a larger number of people can be tested.

QNL: What is the safest way to grocery shop? Wear gloves? Wear mask? Just wipe down the cart? Plastic bags vs. cloth or paper? Wipe all grocery items with disinfect wipes? 

Dr. Clark: At the very least, you should wear a mask of some kind and wipe down your grocery cart handle. If you’re in a high-risk area, you may want to think about taking additional steps including wearing eyewear or goggles since the virus may be able to infect through the eyes, like other respiratory viruses. Gloves probably aren’t going to help. They are more to help keep your hands clean which you can change after touching something that is contaminated. In public, gloves can become just as contaminated as your hands as soon as you touch something. 

I would recommend plastic or cloth over paper for groceries. Viral particles are probably active longer on plastic but bags with handles will allow you to carry the groceries without carrying them against your body. Cloth bags can be washed or isolated with a few days when you’re done using it. 

The biggest danger in grocery shopping is being around other people. We don’t know exactly what the chances are of catching the viral particles from a surface, but it is almost certainly lower than the chances of catching it by breathing in aerosolized particles. To be safe, wiping down any groceries that are in containers or boxes should be fine. If the groceries are non-perishable, you can also isolate them for a few days at room temperature. For fresh fruits and veggies, washing them off with cool tap-water is recommended by experts (without soap which may leave a soapy residue that you do not want to ingest). 

QNL: What about washing our facesWe’re told to wash our hands but I don’t hear anything about making sure your face is washed. I’m just curious about droplets that may land on your face.  

Dr. Clark: The virus has to get to cells that it can infect, and those cells are inside the body. If you did get droplets that contained viral particles on your face, they should only be able to infect you if they are moved from the skin on your face to your eyes, mouth, or nose. By far the most likely way for this to happen is for you to touch your face and then touch your eyes, mouth, or nose. It should be comforting to know that healthcare workers take routine precautions to prevent themselves from getting infected with pathogens which does not include washing their faces. These precautions have been proven to be effective.

QNL: With regards to inhaling the COVID-19 virus, is it more, less or equally likely to enter through the mouth vs. nose passages? 

Dr. Clark: I haven’t read any research on this, but I imagine it would be pretty hard to test. As a guess, I would assume it enters through the nose more often simply because most people breath through their nose more than their mouth in their everyday life.  

QNL: Do we know if those who tested positive had previously practiced social distancing?  I’m curious to know if the reason that the bulk of the people getting sick from the virus is because they weren’t taking social distancing seriously.  

Dr. Clark: It is really hard to tell right now. Infection rates are slowing in countries where strict social distancing has been implemented, which indicates people who are practicing social distancing are probably less likely to get the virus than those who aren’t distancing. That being said, I wouldn’t assume people are getting infected because they aren’t being responsible — it is possible that they were somehow exposed in an unknown way or they may have been an essential worker who was exposed to a large number of people. 

QNL: If we microwave a surgical mask, will it inactivate any infectious viral particles on it? Can PPE (personal protective equipment) be microwaved in care facilities to allow the reuse of gowns, masks, and gloves?  

Dr. Clark: Microwaving isn’t considered a reliable method of decontaminating PPE. Some studies have looked at whether disposable PPE can be reused after being decontaminated with various methods. The most recent one is a pre-print (keep in mind that means it has not yet been peer-reviewed) paper released by the National Institute of Health in mid-April.16 They found that dry heat at 70° C. (158° F.) could be used twice to decontaminate N95 masks before their function declined. Vaporized hydrogen peroxide and UV radiation could be used three times before the mask’s function suffered. This matches what the CDC has reported on a very informative page on their website.  

Coronavirus news in the newspaperCoronavirus news in the newspaper

QNL: Are daily newspapers and mail safe to handle? If they have been touched by someone who has tested positive, how long will newspapers and or mail be contaminated? 

Dr. Clark: There haven’t been any reports of people getting sick from the mail. To be safe, you can assume that the viral particles can stay infectious on mail for about the same amount of time it can stay viable on cardboard: 24 hours. The safest thing to do is just open your mail, dispose of the envelope, and wash your hands, or just isolate your mail for a few days at room temperature. 

QNL: Can a face mask be put in the oven at 180° Ffor some time to sterilize it? If not, why? 

Dr. Clark: There are conflicting reports about this. The CDC references early studies that suggested dry heat compromises the integrity of N95 masks17 but a more recent pre-print study by the NIH16 found that 158° F. could be used to decontaminate the N95 masks. The NIH study determined that it was possible to heat the mask twice before filtration was compromised. But these are recommendations for health care facilities during a crisis. I wouldn’t recommend doing this at home unless the N95 mask manufacturer specifically approves it. There are many different brands and types of N95 masks, so even if we knew that most masks could be decontaminated this way without affecting its proper filtration (but we don’t), some of them may end up being compromised in some way or even catching on fire if something goes wrong.  

QNL: How long are viral particles active on money? What is the best way to disinfect money? How should someone protect themselves from the infection if they have to deal with cash from customers? 

Dr. Clark: To my knowledge, there haven’t been any studies looking at this specifically. I don’t see why viral particles would be active on money longer than other surfaces (2-3 days at room temperature). The easiest way to disinfect money would be just to wait a few days. If that isn’t practical, just be sure to wash or disinfect your hands after handling cash. Unless viral particles on money became aerosolized somehow, you would have to touch the money and then touch your face in order to get infected. If it would make you feel safer, you can look up what cleaning methods can be used on currency you have (different countries use different materials). Almost any cleaning method should at least lower the number of infectious particles on money.  

QNL: Do viral particles stay on a specific spot or do they travel on the object to other parts? For instance, if someone with the virus touched the outside doorknob of my front door, would the viral particles travel to the other side of the doorknob on the inside of the house? 

Dr. Clark: Viral particles can’t move on their own. Like dust, they do not travel once they settle on a surface unless there is significant disturbance. Any time viral particles (or other particles) move, the particles become diluted. I would say it is pretty unlikely that you can get infected from touching something that wasn’t directly touched by an infected person.   

QNL: Our county in Minnesota is surrounded by counties with known COVID-19 cases. Why do we not have any cases even though we are surrounded? 

Dr. Clark: If there has been travel between neighboring counties and your county, it is safe to assume there is undetected spread happening to some degree. It is possible that testing has not have caught up yet. There is also a component of randomness that could explain it since the spread of a disease early in an outbreak is somewhat asymmetrical. You can see this with how the virus spread outside of China—why was Italy the first to see major spread of the virus and not France or Greece, for example? 

QNL: What pre-existing medical conditions make people more susceptible to COVID-19? Why are they causing people to get sick more than others and suffer from complications from this virus? 

Dr. Clark: The CDC characterizes high-risk groups for severe COVID-19 as: 

  • People over 65 
  • People living in a nursing home or care facility  
  • People with chronic liver, kidney, or heart disease 
  • People with chronic lung disease or moderate to severe asthma 
  • People who are severely obese  
  • People who are immunocompromised 
  • People with diabetes 

The CDC also recommends precautions to take if you are in one of those groups. Most of these groups are already at higher risk for most infections because their bodies might not be as able to fight off the infection. Hypertension isn’t listed by the CDC, but it also seems to be associated with poorer outcomes. Researchers haven’t nailed down the exact reason for that though.  

QNL: Thank you, Dr. Clark, for taking the time to answer our questions. We appreciate your expertise.   

You can read our previous COVID-19 Q&A with Dr. Clark by clicking here for part one and clicking here for part two.  


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