The "Discussions" section of Medical Legible is used to transmit information on relevant topics that are both important, and sometimes, unwieldy. Medical research evolves quickly. Constantly. Keeping track of it, synthesizing it, and even putting it to good use can be overwhelming. "Discussions" will attempt to make that a little easier, using up-to-date, peer-reviewed work meant to represent information of the highest quality. For the sake of clarity, "SARS-CoV-2" will be used to refer to the virus itself, and "COVID19" will be used to refer to the syndrome, or set of symptoms, associated with SARS-CoV-2 infection. In-text citations and bibliography in Vancouver style.
Today's topic: updates on COVID19
SARS-CoV-2 transmission, restaurants, airflow
Much of the discussion regarding COVID19 centres around exactly how one can contract SARS-CoV-2. Early discussions at the outset of the pandemic reported live virus particles surviving up to 9 days on certain surfaces, inciting some interesting discussions about how to protect against a virus that never dies. Those initial estimates seem exaggerated today, and current research shows virus detection on most surfaces approaching zero after 72 hours.(1) Viral detection does not necessarily mean infectivity; further to this, the presence of infective viral particles on a surface does not guarantee that you will contract the virus if you came into contact with these infective particles. Infection via fomites (surfaces/objects that carry infection) necessitates the transmission of a suitable viral load from said surface to one of your mucus membranes (eyes, nose, mouth).(2) As such, it has become apparent that aerosol transmission is the main transmission route (The distinction between aerosol and airborne transmission will not be discussed here, but there is a difference!). This does not obviate the need for vigilance with surface decontamination and hand-washing, but simply means that a comprehensive approach to preventing COVID19 must include measures to curtail aerosol transmission. For example, mask wearing.
Pertinent to this, Dr. Sax of the New England Journal of Medicine discusses SARS-CoV-2 transmission specifically in the context of restaurants (3). This is especially pertinent given the multitude of "reopening" strategies ongoing around the world.(3) Two studies of note are highlighted. The first (4) is a retrospective study in the US that compared the behaviours of 314 patients (154 SARS-CoV-2 positive patients, and 160 similar-yet-noninfected individuals). The two variables that differentiated these groups were close contacts with COVID19 and the tendency to go to bars and restaurants. In other words, these were variables that made it more likely for one to get infected. While studies such as this don't confirm a mechanism, they are stark indicators of what policy-makers and healthcare workers should be most afraid of.
A study in China (5) has clarified, with painstaking detail, the factors that could contribute to transmission in public spaces. In short, the argument is that a restaurant environment allows for close, repeated contact between individuals. Transmission can be "aided" by waiters who spend extended amounts of time with multiple tables, thus increasing the likelihood infected patrons transmit to their waiter. Finally, the smaller the restaurant, the more likely air conditioning can help push large droplets and aerosols to nearby tables.
These are only recent examples of concepts we have known for some time; indoor, close contact should be avoided; mask wearing helps prevent the spread of the virus; quarantining when suspicious of an infection can help protect those close to you.
Are SARS-CoV-2 antibodies protective?
The media and politicians spend a lot of time discussing COVID19 testing (and rightfully so!), but the vast majority of these discussions are related to detecting the virus itself. While this is useful in the detection of active cases, treatment, and quarantining, it is useless once the virus has cleared from someone's body. Enter: antibody testing.
Antibodies often hang around our systems long after infections are cleared, preparing us for, or protecting us against, the next infection. This is the concept behind using vaccines to trick our immune systems into making them. Being able to detect these antibodies would go a long way to informing us how many people have had the virus, and also helping us understand whether these antibodies confer any protection to future infection. Detecting antibodies would also help us understand how effective a vaccine is. However, science and technology is frustratingly grey when it comes to its progress, and in medicine, this is often due to the sensitivity and specificity of tests. Let's use antibody testing as an example.
An antibody test (or any test!) is sensitive when it detects the thing it is looking for (i.e. if someone has antibodies, the test goes BEEEEEEP). Tests with high sensitivity don't miss people who are positive. In other words, they have very few false-negatives (someone with antibodies who gets a false "no antibodies" result, in our example). Tests with low sensitivity miss a lot of "positive" people.
A test is specific when it is only positive for the thing you are looking for (i.e. the test goes beep for people with antibodies to SARS-CoV-2, but doesn't go beep for anyone else). A test with high specificity would have little-to-no positive tests for people without antibodies. Tests with low specificity catch a lot of "negative" people.
Think of sensitivity and specificity like a fishing net. A test that is highly sensitive will catch all the fish you're looking for, however, it may also catch other things (like turtles, or garbage). This test is still sensitive (it caught almost all the things you wanted) but it is not very specific (it caught a bunch of stuff you didn't want). A test that is highly specific will only catch the fish you're looking for, and nothing else. However, if the sensitivity is low, it will also miss a lot of the fish you're looking for.
The ideal is to have a test with both high sensitivity and specificity. In the case of SARS-CoV-2 antibodies, you would catch all people you had them (no false negatives), but you wouldn't catch anyone who didn't have them (no false positives).
Early tests for SARS-CoV-2 antibodies in the blood had very poor sensitivity; they were not detecting very many people who had the antibodies. The specificity of these tests was irrelevant because they couldn't do the one job they were designed for. We have come a long way since then. To understand the breadth and depth of efforts to test for antibodies, Johns Hopkins University keeps a list (6) of testing kits designed to detect these antibodies, and includes, among all their details, data on sensitivity and specificity. It is updated twice weekly.
A unique study (7) of a COVID19 outbreak on a fishing vessel is shedding some light on whether SARS-CoV-2 antibodies confer protection to infection. Genetic analysis of the virus revealed the outbreak likely stemmed from one individual. 88% of the 122 members on board became infected. Of the members who did not become infected, 3 already had evidence of antibodies against the virus. The sensitivity and specificity of the tools used to test for antibodies in this study are 100% and 99.63% respectively.(6) In other words, the numbers are accurate. Subsequent statistical analysis showed that the likelihood of these three being protected being due to luck to be less than 0.1%. In other words, their antibodies did protect them.
It is worth noting that despite the strong statistic support in this study, this work alone does not indicate antibodies are the solution. It leaves a number of questions unanswered. Firstly, are these three individuals the lucky few who "held on" to their antibodies after infection, while the vast majority of us lose them shortly after the infection clears? Secondly, how many people are capable of mounting a response like this that is protective? Thirdly, if a vast majority of us can make these antibodies after infection, how long would they last?
Like the previous section on transmission in restaurants, this study (nor any other!) will not be the smoking gun on its own. Its usefulness lies in its combination with volumes of other evidence to paint a cohesive picture. Right now, that cohesive picture should engender some cautious optimism that antibodies are protective against SARS-CoV-2.
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