Tag Archives: epidemic

finally, (some) hard numbers on schools and Covid spread

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This article from The Intercept cites some recent research studies that put some numbers behind what level of community spread would make opening schools unsafe. The basic idea is that school (especially elementary school) is pretty safe when the level of infection in the community is relatively low, because kids coming to school are not that likely to be infected. But when the level of infection in the community rises, kids coming to school are more likely to be infected and further accelerate the spread.

Even educated people in the general public have a hard time with unit conversions, and this article switches between various units within the article. Come on, guys. Anywhere, here are the numbers from a variety of sources in the article. I’ve done the unit conversions (correctly, I think, but this blog post does not constitute medical advice…)

  • 36-44 per 100,000 population per week (~5-6 per 100,000 per day)
  • 147 per 100,000 per week (21 per 100,000 per day)
  • 35 per 100,000 per week (5 per 100,000 per day)

That seems like a pretty big range, and I am also suspicious whether the reporters have carefully checked the math, given how they jump around even within the article. But let’s assume they have it right. The threshold is somewhere between 35-147 cases per 100,000 per week. The Pennsylvania Department of Education recommends a threshold of 100 cases per 100,000 per week to consider in-person K-12 school. (Although private and parochial elementary schools have been open throughout the pandemic, and public school districts are hit or miss.) The official number for Philadelphia county at the moment (I’m writing this on January 7), which they only update once a week, is 225.9 per 100,000 per week and falling. My unofficial 7-day running average of the numbers the Philadelphia Health Department reports in its daily press releases is 235.0 per 100,000 per week and falling (but looking at a plot, I would say it’s bouncing around and not clearly rising or falling this week). Those of us with children in public school have not had the option of in-person school so far during this school year.

“virgin soil epidemics” in the Americas

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This is a seminal 1976 paper by Alfred Crosby on the epidemics that devastated Native Americans after Europeans first came. I’m sure there is plenty of scholarly work since then that may have refined this, but it is horrifying even if some of the details have changed. The most extreme estimates are that as many as 100 million people lived in the Americas pre-Columbus, or one-sixth of all humans alive at the time, and only a few million survived. If true, this is much worse than the Black Death in Europe. This would mean that Native American civilizations might have been equivalent in size and sophistication to European and Asian ones. We just don’t know.

I think this is also a cautionary tale for what a novel disease or combination of novel diseases could do to our current civilization, whether natural or man-made. He does point out though that genetic factors and never having been exposed before were only some of the factors. People at the time did not understand quarantine for example, and some practices for dealing with the dead led to more contagion. People might have been weakened by exotic diseases like smallpox, then finished off by diseases they would have experience with like malaria or pneumonia. They didn’t understand how hydration, nutrition, and keeping warm could keep their strength up to fight off secondary infections, or else people may have been too sick to fetch water and food and keep fires burning. Hopefully we can do much better today if and when some terrible epidemic strikes.