Corona-zona

  As regular readers know, there has been quite a bit of coverage on this blog about mask effectiveness. It forced me to learn about aerosols and how they move around a room and spread the virus. On of the casualties of that learning has been my innocence/naivete regarding how much exhaust from other humans I probably have always breathed in. This new study demonstrates how even normal breathing creates a "saliva plume" that travels some distance from the breather.   The study concludes that "normal breathing indoors without a mask can transport saliva droplets capable of carrying virus particles to a distance of 2.2 meters, or 7.2 feet, in a matter of 90 seconds." Eeww.  That means if you're sitting next to someone who is not masked on a plane, or within seven feet of someone at a bar or restaurant, and they are merely breathing, you're going to be inhaling stuff from their "saliva plume." If that plume happens to include enough SARS-CoV-2 parti...

Yesterday Wired magazine released an excellent  long-form article on how WHO and CDC were dragged kicking and screaming into an admission that they had been wrong about the main transmission mechanism for SARS-CoV-2, and why it took so long to get it right. You may recall that about a year ago, we were being told to keep 6 feet away from other people and wash hands frequently. That's because they thought the main way the virus spread was through respiratory droplets, a.k.a. fomites .  The theory was that an infected person would cough or sneeze, this would release large respiratory droplets that if you were too close, could land in your mouth or nose or eyes—the origin of the six foot rule. They could also land and persist for some time on surfaces, which you could touch and transfer the virus to those same openings.   Believing this was the main infection route, people were washing packages and vegetables from the grocery store in bleach.  There were shortage...

  Here are some updates on previous Corona-zona posts. Toilet Aerosols…Ewww Previous posts have discussed how the virus spreads, mostly focusing on how masks stop transmission of aerosols emitted from one’s mouth. Now there’s a new potential source.   It has been known for some time that SARS-CoV-2 can infect one’s gut and be expelled with feces. Those feces (hopefully) go into a toilet, and guess what happens when you flush the toilet.   You get aerosols, lots of them .   According to a scientist quoted in the article: Both the toilet and urinal generated large quantities of droplets smaller than three micrometers in size, posing a significant transmission risk if they contain infectious microorganisms. Due to their small size, these droplets can remain suspended for a long time. As the article points out, there are no documented cases of COVID-19 being spread this way. But it is a possibility. Gnome Shortages Back in January, I did the first post abo...

  Lately we've been hearing a lot of news and fretting about mutations in SARS-CoV-2. There are variants associated with the UK, South Africa, and Brazil.   Current thinking is that these versions are more contagious.  I've heard two theories for why this may be true. One is that the virus might be better at reproducing inside the body, creating a higher viral load, meaning the victim would shed more viral particles when contagious. This makes it more efficient at getting from victim to victim. A second is that mutations improve the "spike protein" the virus uses to bind to a cell, allowing it to inject its payload and hijack the cell's machinery. This makes the virus more efficient at invading cells once it has entered your airway.   One study summary I read says that there are not only spike protein changes but other changes too, which taken together make the virus a more efficient invader.  This includes possible changes that may help the virus eva...

  This week the CDC released a report on COVID-19 trends among people 24 and younger. It contains good news for those of us, especially beleaguered parents, who want to see their kinds back in school. Reviewing data from March 1 to December 12 of last year, they found that the prevalence of cases decreases with age. Here is a pie chart based on numbers in the report:  Moreover, they found that there doesn't appear to be much difference between infection rates in counties that did offer in-person instructions and those that did not: As of December 7, nearly two thirds (62.0%) of U.S. kindergarten through grade 12 (K–12) school districts offered either full or partial (hybrid with virtual) in-person learning. Despite this level of in-person learning, reports to CDC of outbreaks within K–12 schools have been limited, and as of the week beginning December 6, aggregate COVID-19 incidence among the general population in counties where K–12 schools offer in-person education (401.2 p...

Remember when public health experts were warning us not to travel over the holidays?  In case you don't, here's what Dr. John Brownstein, chief innovation officer at Boston Children's Hospital said two days before Christmas: Layering in the December holiday travel and gatherings means we will have a third jump in this wave, or a surge on surge on surge. Unfortunately, this increase will likely lead to catastrophic impacts on hospital capacity and the acceleration of terrible mortality milestones through February. The chart at the top of this post shows new cases in Maricopa County per 100K people, seven day trailing average. It is my  favorite chart from ASU's Biodesign COVID-19 Dashboard.  Notice that things change right around January 1.   Harvard  says the incubation period for COVID-19 is from two to 14 days, but symptoms normally appear after around five days.  So there is a plausible story here that people traveled for Christmas, stayed a...

  A team of mechanical engineers and chemists from the University of Wisconsin at Madison (UW) have a cool study in pre-print (meaning it's not been peer-reviewed yet).  They set up a bunch mannequins in an actual classroom (as pictured above).  They configured some of the mannequins' pie-holes to exhale aerosols and others to inhale the surrounding air.  They actually tried several different scenarios for placing the exhalers and inhalers, which you can read about in the paper if you're interested. The aerosols they used were salt particles engineered to be about the same size as aerosolized SARS-CoV-2 particles.  They note that the concentration of particles was higher than someone with COVID-19 would actually emit, but they had to do this to ensure they could measure the test aerosols (signal) above the aerosols naturally present in the room (noise). To test transmission, they put different masks on the dummies:  4-layer commercial cotton masks, cloth m...

A new study by the CDC indicates that at least 50% of transmission of SARS-CoV-2 is by people without symptoms.  They arrived at this conclusion using a mathematical model.   There is an old aphorism  (attributed to the famous statistician George Box): All models are wrong, but some are useful.  They are wrong because they are always only approximations of reality, and involve assumptions.  They are useful when they incorporate many of the important factors (but not too many factors) and carefully justify their assumptions. The CDC study seems to fall in the latter category.  It is not overly complicated.  It assumes that infected people fall into two groups, those who transmit the virus before symptoms appear and those who never develop symptoms at all.  Quite a bit is known about how symptomatic infections proceed and the model takes that knowledge into account.   There is uncertainty about how many people fall into the never-sym...