California May be Poised to Experience a Rapid Increase of COVID-19 Cases

In an earlier post I expressed my hope that California would escape the worst of this crisis. I'm not alone in this. The model of the Institute for Hospital Metrics and Evaluation (the one quoted most often by the White House) indicates the peak of the crisis occurred 5 days ago (April 18). The Model Consortium of The University of Texas at Austin puts the odds that California has passed its peak at 72%.


But I am no longer as optimistic as I was, nor as these models indicate. New case counts in California have resumed their upward trend. Beyond that, It's not only that they are going up. It's also how they are going up. In any analysis you want to avoid including dissimilar things in an average. Doing so obscures potentially critical insight.


Growth of new cases is exploding in Los Angeles, while they are flat in the rest of the state. Just looking at state-wide data causes one to miss the extent of Los Angeles' recent, rapid growth. Below is a chart of case counts (7-Day moving average) in Los Angeles County through yesterday (April 22). Recent growth in new case counts is now greater than when this crisis began, which is not an encouraging sign.


Note the growth in cases over the past three days. I've been reviewing these sorts of data for two months. I rarely have seen that strong a trend in new cases quickly reverse itself. But it is possible the increase is merely due to LA County catching up on its reporting. Time will tell.


Now compare Los Angeles' growth with the rest of the state (shown below). Daily new cases have been mostly been flat over the past two weeks with a slight downward trend over the past couple of days. Unfortunately, that downward trend is now overshadowed by Los Angeles' new cases. LA now represents over half of daily new cases in the state. So, its trend will dominate California's results unless there is a fundamental change.


While the slight downward trend for the rest of California is encouraging. It isn't so great that the trend couldn't reverse itself. Bottom line; neither of these charts provide confidence California's peak has passed.

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