New Covid-19 cases are increasing in five metro areas: Phoenix, Tucson, San Antonio, Tampa and Raleigh

These are the places to watch to see how well re-opening plans manage to avoid re-igniting the pandemic.

Metro areas, not states, are a better lens for monitoring Covid-19.

We’ve been tracking the spread of the Coronavirus for the past three months. The good news is that the spread of the disease has slowed sharply almost everywhere since cities started implementing stay-at-home orders in mid-March. In the past several weeks, a number of states and cities have started the process of re-opening, and naturally everyone is apprehensive about the prospects of reigniting the pandemic if we haven’t taken sufficient steps to continue social distancing, and effectively implement test, trace and isolate programs.

While the overall trend in growth of new cases is still slowing across metropolitan areas, several cities are seeing noticeable spikes in new cases. We measure new cases growth as the daily average percentage increase in the number of reported cases over the past seven days. Our data are from the New York Times database and cover the period through Monday, June 8.

Five metropolitan areas show an unmistakeable acceleration in the spread of the virus in the past several weeks. Since Memorial Day, Phoenix and Tucson have both seen their rates of growth more than double from less than a 2 percent daily increase in the number of cases to increases of 4-5 percent per day. Raleigh’s rate of increase has been trending upward since Mid-May, and has doubled to more than 4 percent now. Tampa and San Antonio have also seen an acceleration in the spread of the virus.

All of these cities bear close watching in the next few weeks. Will the rate of new cases continue to increase, or will the test-trace-isolate efforts be sufficient to check a rebound in the pandemic? Will hospital resources be over-taxed by the scale of the rebound?

The patterns of these data are a reminder that metro areas, rather than states are likely to be a better unit of analysis for detecting trends in the spread of the virus. While all of Arizona seems to be seeing a surge in cases, there are definite variations among metro areas in states like Texas, Florida and North Carolina. North Carolina’s statewide growth rate in new cases actually decelerated between late May and early June (from 3.4% daily to 3.0% daily), and the statewide increases in Florida and Texas were much more muted (0.4 percentage points increase), than in Tampa and San Antonio, respectively. (State data from 91-Divoc). Metro areas correspond more closely than states to the geographies where people live, shop, recreate and socialize, and therefore are a better lens for tracking Covid-19.