Analytic Section Missing from Original Post
What Does the Chart Suggest?
There are no definitive answers for the US based behavior of the Covid-19 novel virus. But there are approximations possible that can be useful while the storm is upon us, subject to revision and always seeking the best and most complete data to support decision making by responsible parties, including the general public. Take them with a large grain of salt and be cautious.
The time it takes for reported cases to double in the United States is a question of intense interest. Understand that we know reported cases are only a portion of actual infections, but that number will never be known exactly. So, this is a rough substitute with some undercount, i.e. it is likely to be conservative, not exaggerated.
Two weeks of US national data show that reported cases rose from 100 to 1,600 in 10 days from March 2 through March 12. That implies that there were four doublings in 10 days, and that the estimated doubling time for US cases is 2.5 days or thereabouts. Back of the Envelope. Rough, but not that far off expected value.
If the cases double every 2.5 days, they will more than quadruple every week during this phase of spread. Since the rate is fairly constant over the nearly 2-week period, we might reasonably expect that a week from now there will likely be at least 6,400 cases in the US.
I have included comparable data from Germany and Italy for a quick check. Italy shows 3 doublings from 1,600 to 12,500 in the 10 days from March 1 through March 11, suggesting a doubling time of about 3.3 days there. German data shows 3 doublings from 200 to 1,600 in the 7 days from March 3 through March 19, suggesting a doubling time there of about 2.3 days.
In any case a planning estimate that US cases will only double each week for now is seems to underestimate the problem by rather a lot, particularly for further distant times periods. This viral spread in the US right now is hot, very hot.
The estimates are not a guarantee, but a defensible proposition, subject to correction based on new data input as often as possible. Data to improve the estimates is provided every day, reducing lag time for correction.
One other comparison that has been made on TV is how many days we are behind Italy or Germany or France in our growth curve. This chart provides a visual calculator to address that summary question directly.
As of today March 12, the US is roughly 2 days behind Germany. The US is apparently about 10 days behind Italy, with a caveat. The JHU tracker shows the total number of Italian cases for both March 11 and March 12 to be 12,462. The WHO data base shows the same total today. This is clearly an error. I suspect the Italians are so busy treating patients with Covid-19 and administering public health measures they were not able to fully update their case reports in the last 24 hours. How much of a delay there will be is not known, though the data seem solid up until today. Godspeed to all the Italian caregivers, first responders, public health officials, government workers, and Italians sickened and affected by this novel virus.