Weekly COVID-19 Data Update, June 18: The Regional Gap Widens

The gap between early US epicenters and states with new upticks in case counts increased this week. Across the hard-hit Northeast, new COVID-19 cases fell below 2,000 per day: a cause for celebration. But Arizona alone saw more new cases on June 16 and June 17 than the entire Northeast region, which includes Connecticut, Massachusetts, Maine, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont.

Arizona was not alone in rapid new case growth this week. Thirty states have seen cases rise over the past seven days, and in some states that rise has been very steep. In Texas, cases are up 44 percent since last week. In Arkansas, they were up 41 percent. In Florida, cases have spiked 78 percent.

How much of this rise in cases is attributable to increased testing? As daily US tests move toward the 500K tests per day minimum recommended by the Harvard Global Health Institute, we would expect to see a corresponding rise in case count. We can evaluate whether the regional increases are due to more testing by looking at two other numbers: the positivity rate of all tests performed, how many tests came back positive—and hospitalizations. In regions where testing capacity has caught up to the outbreak, the positivity rate drops, which is what we see in the Northeast, where the positivity rate has dropped from above 40 percent to below two percent.

After dropping from April highs, the positivity rate in the South and West plateaued and then began to rise again, meaning more of the tests being performed are coming back positive. At the same time, we’re seeing COVID-19 hospitalizations rise sharply in some areas. Since Memorial Day, Texas has seen an 84 percent rise in COVID-19 hospitalizations; in Arizona, hospitalizations have risen 90 percent over the same period.

Against the background of rising cases and positivity rates, no US state has yet re-imposed restrictions on businesses or gatherings. Since May 20, all 50 states began the process of phased reopening plans. So far, only Oregon has halted further reopening until their state-level data improves. In Texas, where restaurants are allowed to operate at 75 percent capacity, reopening is continuing as planned and mask requirements are no longer enforceable. In Arizona, however, although official reopening plans remain in effect, the governor has issued an executive order that requires businesses to comply with (previously voluntary) social-distancing guidelines and allows cities and towns to impose new face-covering requirements.

The most positive news from this week’s data is that known COVID-19 deaths have continued to decline from their April peak, which was heavily concentrated around the Northeast regional outbreak.

Although death counts are known to be a lagging indicator, the full duration of the lag is becoming clearer. Vital Strategies, a global public health organization originally focused on preventing lung disease, explains the delay this way: 

According to current CDC modeling parameter best estimates, it takes on average about six days to develop symptoms after an exposure, 15 days from symptom onset to death, and seven days from death to reporting, for a total of about 28 days from symptom onset to death. It is important to remember that these are rough estimates and in practice this timeline can vary a great deal from one individual to the next.

Given this lag, deaths are not a useful early indicator for monitoring whether the disease situation is worsening or improving. Practically, this means that to assess the impact of changes (e.g. loosening or tightening) of public health and social measures, one would have to wait several weeks before any change is detected.

If the average lag between symptom onset and death reporting is roughly 28 days, as suggested by the CDC, we should see this week’s death counts as the result of COVID-19 infections from the week leading up to Memorial Day. We would look to next week’s death numbers to reveal more about the outcomes of new cases from Memorial Day gatherings and reopenings.