“Coronavirus Surge in Tulsa ‘More Than Likely’ Linked to Trump Rally: Dr. Bruce Dart, the director of the Tulsa Health Department, said Tulsa County had reported nearly 500 new cases of Covid-19 in the past two days.” So read the headline in a July 8 report in the New York Times.
Plotted in the graphic above are the daily counts of new COVID-19 cases reported by the Tulsa Health Department through July 8, each date represented by a sky-blue-filled circle. The counts are measured on a logarithmic scale, as indicated on the left-hand vertical axis. The arrow indicates the timing of the June 20 rally.
In a separate report on the same date, entitled “Tulsa health official: Trump rally ‘likely’ source of virus surge,” Politico noted, “Tulsa County reported 261 confirmed new cases on Monday, a one-day record high, and another 206 cases on Tuesday. By comparison, during the week before the June 20 Trump rally, there were 76 cases on Monday and 96 on Tuesday.”
The graphic below reproduces the first data plot with some annotations. The orange-filled circles highlight the four data points mentioned in the Politico report. While there has been considerable day-to-day variation, counts of new COVID-19 cases were increasing for about one month before the rally, and continued to increase after the rally. Superimposed on the plot is the ordinary least squares regression line for the data from May 10 through July 8. The slope of the blue line (0.0543/day, St. Err. = 0.0042, P < 0.001) implies a significant exponential doubling time of 12.75 days during this period.
In the third graphic below, the counts of new daily COVID-19 cases in Tulsa are overlaid by the trend in the Google Mobility index for retail and recreational activity in Tulsa County during the same time period. This social mobility indicator, graphed as a connected red line, is measured along the right-hand vertical axis as a percentage change from baseline, which Google calculates as the median value for the 5-week period from January 3 – February 6, 2020.
In the fourth and final graphic below, the counts of new daily COVID-19 cases in Tulsa are superimposed on the combined daily census of COVID-19 patients in Tulsa hospitals. The patient counts are restricted to Tulsa County residents.
The data show that over the past two months, Tulsa has been confronting exponential growth of confirmed COVID-19 cases with an estimated doubling time of 12.75 days. The observed growth of COVID-19 case counts is paralleled by an increase in at least one indicator of social mobility. The growth in newly diagnosed cases is further consistent with the rising census of patients hospitalized with complications of COVID-19, a more sensitive indicator of the demand for high-level healthcare resources. The latter rise in hospitalizations contradicts the hypothesis that the observed surge in cases is merely the result of increased testing among individuals with mild, self-limited disease.
The above-cited press reports relied upon a news conference given by Dr. Bruce Dart, the director of the Tulsa Health Department. Dr. Dart did not explicitly identify President Trump’s rally as a contributing cause of the epidemic surge. It appears that the Tulsa Health Department has been engaged in extensive tracking of the hundreds of newly diagnosed cases. The results of such case tracking could be highly informative about the contribution of the June 20 rally to the continuing rise in new infections in Tulsa.