Monday, Aug. 3Welcome to another school week. Here is a quick status update for today. I have included a pull of all the cases for the geographically defined Central Savannah River Area (CSRA). There were 2,347 cases in the past seven days, which is also 43.6 cases per 100,000 people per day. That is how health agencies typically evaluate the level of community transmission.There are about four infections for every case still, as the people with low or no symptom loads typically do not get tested. The local hospitals are being tracked by WRDW:https://www.wrdw.com/content/news/By-the-numbers-Latest-stats-on-coronavirus-in-the-CSRA-569481341.htmlWe have 238 COVID-19 hospital inpatients in the CSRA. With our population of 768,000 people, that is 309 COVID-19 inpatients per one million people. Georgia has 291. For reference, the Brownsville-McAllen area of Texas peaked at over 1,100 inpatients per 1 million people recently, while Miami-Dade had 850 and the Phoenix region had 500-600. The New York City metro area in the spring was also over 800.Some area colleges, as well as some area primary and secondary schools, are beginning today.If we want to calculate the probability that someone is currently infected in our room, we can use a simple first order approach. What is the independent probability that each person is not infected? In a room of 20 people, with an infection rate of 1.75 percent, the probability will be (1.0-0.0175) raised to the 20th power. That calculates to a 30 percent chance. If we remove a quarter of the sick folks from the population because they tested, it goes down to a 23-percent chance. If we have a class of 50 people, the probabilities are 51 percent and 41 percent.It should be plain to see that if you have a school with multiple classes of 20+ students, it will not take very long before someone who is transmissible is transmitting in a classroom.These probabilities change a lot when community transmission is lower. Those classes of 50, if infection rates were 10 times lower, have probabilities of someone infectious being present of only 6 percent. With good mitigation and surveillance, we could stop a breakout like that. However, I fear we cannot stop accelerating breakouts even in classes of 20 people with the infection rates seen today.
Contact Dave Blake.