Infection and Testing Rates for COVID-19

There is no denying that our current picture of COVID-19 cases is grossly incomplete. We are not performing mass testing. Only those that meet a number of criteria are tested. Data from the Diamond Princess cruise ship indicate that half of the individuals who tested positive for corona virus are asymptomatic. Therefore, the large number of individuals not exhibiting symptoms combined with the lack of testing will surely lead to an under counting of infections. The confirmed cases will be much lower than the actual number. What should also be considered is that as we look at our daily reports, we must keep in mind that we are in fact looking at significantly delayed reports. We will miss the rapid growth and peak in cases. We will likewise miss the time the infection rate starts to drop. The following graph from Worldometer for the state of Virginia demonstrates this analysis based on the work by the IHME COVID-19 health service utilization forecasting team:

Above copied from Worldometer

The number of daily tests (shown in blue) is clearly lagging the estimated number of infections. As a result, the number of confirmed infections (orange curve) is well below the estimated number of infections (dotted curve). The state of Virginia may easily have reached the peak in mid-April (roughly three weeks ago) but with tests still catching up, the confirmed number of cases per day will not appear to have reached any peak up to this day.

Of course, the dotted curve (estimated number of infections) is simply a guess with a huge band of uncertainty. What serves as a strong backup to this estimate is our understanding of exponential growth. Yes, we have seen during the past few weeks logarithmic plots. These plots do help us see if something is growing exponential or not. And here is the current picture for all the states in the country (Virginia and the entire US are highlighted):


Here, using the number of confirmed cases, the growth of COVID-19 cases is no longer exponential across the entire country, including the state of Virginia. And keep in mind, these are only the cases that have been confirmed. This is both under counted and significantly delayed.

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