By: Kyle Freese, PhD, MPH

Weekly Summary 5/4/2020

This week, Governor Ducey extended the statewide stay-at-home order until at least May 15 (the original order was set to expire May 1). Days prior, he announced a 3-week “testing blitz” that would occur on the weekends. The ultimate goal is to double the number of tests in Arizona.

First, let us take stock of the current national and local COVID-19 situations. According to Johns Hopkins University, the U.S. has passed over 1 million confirmed cases and 63,000 confirmed deaths. But, as we are learning, both figures are likely vastly underestimated. This is important for 2 reasons (though further research is needed to confirm): 1) there are undoubtedly many more asymptomatic and mild cases that are not included in these counts and as a result, 2) we do not have a precise measure of many of the epidemiologic metrics we use to quantify an outbreak’s impact. Together with diagnostic testing with relatively low sensitivity (which can result in more false negative results- i.e. those with the presence of disease would have test results indicating the absence of disease), our ability to fully understand the magnitude of spread of the novel coronavirus is diminished.

In Arizona, our testing is lacking. As of today (May 1st), there are roughly 8,000 confirmed cases of COVID-19, 330 deaths, but only 75,000 tests have been administered. The figure below is from the AZDHS dashboard and shows the number of tests by Arizona county. As a reminder, Arizona has a population of 7.2 million. We have effectively tested just over 1% of the population. Though it is possible to estimate the statewide burden with a representable sample of few individuals, this is almost certainly not the case given the caveats mentioned above. Think of watching live political election results; networks typically show the number/ percent of votes cast for each candidate as well as the number of precincts reporting. It would be cavalier to confidently report a winner based with less than 2% of results available. Similarly, we need to be cautious of the conclusions we are drawing from these limited data.

Figure 1. Number of COVID-19 tests by Arizona County. From the Arizona Department of Health Services. May 1, 2020.

What should we expect for May?

                  Week before last I asked the question “are we passed the peak?”. At the time of writing, there was some evidence that Arizona might be slowing in term of the number of new daily cases (again, given the current limitations in testing deployment). As the week progressed, my cautious optimism faded. In fact, since new data became available several hours ago, there has been an significant uptick in cases (Figure 2 below). As a point of clarity, I cannot comment on whether this increase is a function of 1) an actual increase in cases or 2) increased testing or 3) a combination of new cases and testing.

                  Regardless, these data taken alongside the upcoming “testing blitz” and increased pressure for reopening businesses will prove a slippery course to navigate. Do not be surprised if over the next 2 weeks (right as Arizona is beginning to “reopen”), Figure 2 shows an increase and even a spike. I will stay cautiously optimistic because I believe the social distancing measures that have been implemented are having an impact, but policymakers need to be very careful as they begin to “loosen the hose spigot”. The national guidelines say as much, but to reiterate, those in charge must increase the quantify and improve the quality of testing, closely monitor new cases and potential geographical and demographic hotspots, and remain agile to reinstate restrictions if cases begin to increase.

Figure 2. Number of COVID-19 cases and related deaths. Data from the New York Times case tracking effort.

For additional references, resources, or questions, please email Dr. Kyle Freese at