Masks, Drugs, and Serological Testing!

The world went crazy with masks in the past few days, people in high places are promoting unproven drugs to treat coronavirus, and the new buzz, serological testing. Let me unpack them for you.

Masks:

Masks are useful, but they are not an excuse to drop your guard while in public. I posted an article a week ago on how to make one that will provide better filtration than most https://erinbromage.wixsite.com/covid19/post/time-to-rethink-the-face-mask

Unless you are properly wearing a N95 respirator, all other masks are worn to prevent you infecting other people, not necessarily stop you being infected. They do reduce viral loads a bit, but not a lot.

If you are going to wear a mask, you must also then assume that your mask will be contaminated, either on the inside from you, or on the outside from others. Remember you are filtering a huge amount of air through a small surface that catches and retains microbes.

You absolutely must wash you mask regularly, or in the absence of daily washing, use a household iron, on high heat, for about 1 minute.

Drugs:

President Trump can not help himself and he keeps giving out medical advice based on his gut feelings. Medicine doesn't work on feelings or beliefs, it works on evidence. The president said yesterday "give HCQ a chance, give it to everyone who is sick, what have you got to lose?", well Mr President, you could lose sinus rhythm for a start.

There have been 4 published trials with HCQ (hyrdoxyquinalone), 2 of those trials have shown minor improvement in outcomes and 2 of those trials have shown no improvement. All of the trials were designed poorly, and conclusions from those trials are dubious at best. More to the point, if HCQ was efficacious, we would see it unequivocally in the data. No studies have shown this. Evidence may be come that it does help, but at this stage, the data does not support its widespread use.

Yesterday, Australian researchers found that a common anti-parasitic drug Ivermectin, when used in vitro, resulted in a 5000 fold drop in virus titer. Again, promising results, but this was in a petri dish and human trials need performed before we read too much into it https://www.sciencedirect.com/science/article/pii/S0166354220302011

Please don't get ahead of the science and try and dose yourself with this drug.

Serological testing

Serological testing, or antibody testing, will be rolling out in the coming week or two and the data will be revealing. It will give us the first glimpse of how many people may have already been exposed the SARS-CoV2. Basically, we know that if you have been infected with the virus and recovered, within about 10 days your body will have made IgM and then IgG antibodies against the spike protein found on the virus. If IgM is positive, it means you have had a very recent infection, if IgG +ve, it means you were exposed and recovered some time ago.

Importantly, while having IgG titers against the virus should be a good thing, we just don't know yet if this means you are protected from reinfection, or if you are protected, we don't know for how long.

Another very important caveat, and this IS important. This diagnostic tool will be great, potentially a game changer for how we manage the outbreak. But we need to tread very carefully.

Why?

Well we know these tests are ~93.8% sensitive and have a specificity of 95.6%. This sounds great, right? Well, sort of......

Currently, we know that there are 350,000 people in the USA that have had COVID-19. This is 0.1% of our population. If these numbers are accurate (which they are not, but let's just assume they are), if you take this test and get a +ve IgG response, due to the math associated with clinical testing (specificity, sensitivity, and infection rate) it means that there is only a ~4% chance that this positive was correct. Basically, lots of false positive results.

If the true infection rate was 5% of our population, a positive test would mean that you have a 50% chance of this result being correct. Would you want to make a healthcare, or life decision, on a coin flip? You would be right as often as you are wrong.

Anyone, that is inclined, here a great calculator to play with https://calculator.testingwisely.com/playground/5/90/90/positive

It is only when we get up to >10% of your population who have been exposed, does the rapid test start to have meaningful results. For the time being, while COVID-19 is still relatively rare in our population, any rapid test needs to be validated by a lab-based ELISA before making decisions and those tests are still being developed for prime time (we will have them soon).

For example, it has been proposed that we test health care workers, and any Doctors and Nurses testing IgG+ve will be put on the very front line working with the sickest patients.

This is a great strategy, it's a big part of how we controlled smallpox before the vaccine became available (the ring strategy of quarantine), but when the odds of the test's results are considered we may be lulling our self into a false sense of security.

Stay safe! Be Nice! Do something good for others!