3/30/2020 UPDATE: Based on the last 24 hours the fatality increase from COVID19 was 12%, which was what I used here on 3/15/2020 for this article's original post for estimating how fast ICU beds can fill up in any hospital. Math, and knowledge is power to prepare. "Fear is a reaction, courage is a decision." Winston Churchill
The Rule of 70? Maybe you are not a science person. Maybe more business, finance, and accounting, or more in the arts and theatre. Maybe you are in the trades or other technologies or the culinary arts. Maybe you are familiar with getting a mortgage, or the stock market, bonds, and compound interest? Well, then you may already be familiar with the Rule of 70, and you may already understand what I am writing about in the rest of this article. Why the United States and many other countries can be in the same state where Italy is now in less than two more weeks. Hospital beds full of COVID19 patients, mostly older, some younger, smokers, vapers, those with pre-existing conditions like asthma, heart disease, or diabetes. Not just all the hospital's ICU beds, but all of its beds. Why social distancing and isolation is essential now, without cheating and going to clubs, concerts, restaurants or large gatherings.
The rule of 70 is simple. If you know the percentage growth rate of anything, like population, or patients infected by a pandemic disease, then 70 divided by the percentage growth rate will give you the doubling time. In the case of COVID19, the spread of infection in many world populations so far indicates a doubling time of 5 to 7 days, so let us use 6 days as the average. 70 / 12% growth per day gives us 6 days. "Twelve percent," you say, "Is that bad?"
Yes, that is bad, because once you see just a few COVID19 patients admitted to a hospital's intensive care unit (ICU), the 12% per day growth rate works like compound interest. The result is that a very large hospital with a very, very, large number of ICU beds, say 100, will be overloaded in less than one month. Doubling in growth mathematics is essentially an exponential process. A gentle sloping increase in numbers can go on for many weeks, and then quickly in the space of fewer than two weeks, such a hospital may have all its ICU full of critical patients. Then all the other beds in the hospital too. We do not have a ventilator available for every bed in a hospital, and yet most admitted patients may need a ventilator to have a chance to recover. This is in fact what has happened in Northern Italy.
I made the above graph in Excel and Google Sheets and also posted the spreadsheet for use by teachers or anyone below. (See links at the end of this article). As you can see in this example, the hospital's ICU has 15 COVID patients on day 1. Even one week later, this very large hospital (most do not have anywhere near a many as 100 ICU beds), has less than 50 critical patients and less than 100 after two weeks. Then they are suddenly overwhelmed over capacity by about 50 patients in week-3 and in week-4 there are more ICU patients non-ICU beds. There are not enough ventilators to help prevent many patients from dying. Also, typical car accident patients, heart attack victims, other seriously ill patients go to Emergency Rooms which are already mostly filled with COVID19 patients and there are no more ICU beds, and even no regular beds available. Health care staff are also getting ill and soon doctors, nurses, and their assistants are become exhausted too.
The result is what is being experienced now in Italy, a very modern country with a very modern and well-equipped health care system on par with the United States. Italy, in retrospect, did not enforce social distancing, they left it to be voluntary and many people traveled, went on vacations, went to clubs and restaurants and spread COVID19 even faster. If you feel quite fine now while you are reading this, you may still have COVID19 but be asymptomatic for up to two weeks. At this time you and I could be potentially spreading it to others at home and at work. The "bomb" of patients will be seeded and then suddenly and exponentially explode in our hospitals in a few weeks.
I recommend reading the following article that contains an English translation of an Italian MD's Facebook posting about what has been happening at his hospital. If you have friends or family who are skeptical about our need to prevent the spread of this disease, please share this information with them. By doing so, you will be contributing to saving someone's grandparent, parent, sibling, or child. Maybe even your own. Be a part of breaking the chain. We can do that, together.
Italian Doctor's Coronavirus Experience - by Annie Reneau
Rule of 70 Lesson Sheet - Model of Communicable Disease Population Increase, CLICK HERE to get the google sheet or here to download the Excel version.
The Science Ranter