Corona Episode 19: Viral Exposure and the Frontline of the War
Our world has changed. The other day I was at our local Target and someone coughed, the whole place stopped and you could hear a pin drop. Think about a pediatrician’s office and a small waiting room with 10 sick kids. Just weeks ago all of that would have been commonplace, now it’s our worst nightmare. Because our perception of illness has changed, it’s time to begin talking about the concept of viral exposure and loads. What does that mean and how can you use that idea to help keep your family safe.
What Does “Viral Exposure” or “Load” Mean?
In this context, viral exposure means how much of the coronavirus you get exposed to at any given time. The basic concept is that people that get exposed to small amounts of the virus over time are likely to build some immunity and have a mild case of the virus. People who get exposed to much more of the virus at one time are more likely to get a more severe COVID-19 case. Viral load is the amount of the virus you get exposed to or the amount in your body at any one time.
Does the Coronavirus Behave this Way?
The real answer is that no one really knows.
On the one hand, we know that respiratory viruses like the flu follow this rule. Meaning the higher the dose of the virus you get, the sicker you get (1). In addition, the more of the flu virus you have in your system, the more likely you are to have symptoms (2).
So far, nobody has tested this virus in the same way as the influenza virus was tested above, where patients were exposed to increasing amounts and then their disease course was followed. Hence, we won’t know for a while if this is the case with the novel coronavirus.
However, two research teams did test the amount of virus in the system of patients to see if it correlated with the severity of the disease. In those two studies, which HAVE NOT YET GONE THROUGH PEER REVIEW, more virus in the blood or throat didn’t correspond to more severe disease (3,4). However, in a third study that WENT THROUGH PEER REVIEW AND WAS PUBLISHED in a prestigious journal, the researchers took samples from the nose and there was a strong correlation (5). Meaning people with a higher load of coronavirus in their nose had much more severe disease.
Hence, as a physician, if I were placing a bet on whether the amount of coronavirus you come in contact with determines if you get a mild or a severe case of COVID-19, I would bet in the direction of this virus being like many other respiratory viruses we know. That means that until proven otherwise in actual published papers, it’s likely that being exposed to more virus is correlated with more severe disease.
Things You Can Do to Reduce Viral Exposure and Load
Here are the rules that I use with my family for the foreseeable future:
- If you are NOT SICK STAY OUT OF THE HOSPITAL. This makes sense, as this is where the highest viral loads in your community live. Regrettably, this will still be the case for the next 1-2 years as we fight this bug. Hence, when surgeries spool back up, there will be some controversy about whether we even want to take middle-aged and elderly patients back to hospitals for routine surgeries.
- If you’re not sick, stay out of medical practices who are treating or diagnosing COVID-19 patients. These are usually family physician offices and urgent care practices. These would be the next level down in viral loads. If you are sick, call your doctor or get on a telemedicine portal to avoid going into a clinic treating COVID.
- Stores that are still open like the grocery, Walmart, or Target would also likely have higher viral loads. First, try their delivery services. If you go into the store, then keep a careful watch on what you touch and don’t touch your face until you have washed your hands. A good practice is to bring a clean reusable bag from home and use that to carry your items to the cashier, rather than a shared shopping cart.
These are places with likely lower viral exposure:
- A private specialist’s clinic that’s limiting patient flow and maintaining excellent sterilization practices. Again, make sure that the clinic doesn’t act as a primary care site for COVID-19 cases. Ideally, this clinic should not be located on a hospital campus.
- Your place. Clean all shared surfaces a few times a day with a disinfectant.
The upshot? It’s more likely than not that the amount of virus you get exposed to is important. We could also find out something different at some point. In the meantime, stay safe out there!
(1) Memoli MJ, Czajkowski L, Reed S, et al. Validation of the wild-type influenza A human challenge model H1N1pdMIST: an A(H1N1)pdm09 dose-finding investigational new drug study. Clin Infect Dis. 2015;60(5):693–702. doi:10.1093/cid/ciu924
(2) Hijano DR, Brazelton de Cardenas J, Maron G, et al. Clinical correlation of influenza and respiratory syncytial virus load measured by digital PCR. PLoS One. 2019;14(9):e0220908. Published 2019 Sep 3. doi:10.1371/journal.pone.0220908
(3) Cerada D, et al. The early phase of the COVID-19 outbreak in Lombardy, Italy. Prepublication on Arxiv. https://arxiv.org/ftp/arxiv/papers/2003/2003.09320.pdf Accessed 3/31/20.
(4) He X, et al. Temporal dynamics in viral shedding and transmissibility of COVID-19. Prepublication of Medrxiv. https://doi.org/10.1101/2020.03.15.20036707 Accessed 3/31/20.
(5) Liu Y, Yan LM, Wan L, Xiang TX, Le A, Liu JM, Peiris M, Poon LLM, Zhang W. Viral dynamics in mild and severe cases of COVID-19. Lancet Infect Dis. 2020 Mar 19. pii: S1473-3099(20)30232-2. doi: 10.1016/S1473-3099(20)30232-2.