Fig. 3: Logarithmic plots of confirmed cases by date of symptom onset in China and Italy. | Communications Physics

Fig. 3: Logarithmic plots of confirmed cases by date of symptom onset in China and Italy.

From: The impact of travel and timing in eliminating COVID-19

Fig. 3

a The daily number of confirmed cases in China—by date that these patients self-reported as the onset of their symptoms—are shown as dots on a logarithmic scale. The solid lines are the best ordinary least squares linear fits to the natural logarithm of the number of cases: For Jan. 11-23 (up until the lockdown), the slope (in units of day−1) is 0.228 (R2 = 0.991, 95% confidence interval (CI) [0.214, 0.242]), which corresponds to a doubling time of 3.04 days. For Feb. 2-5 the slope is  −0.145 (R2 = 0.999, 95% CI [−0.160, −0.131]), which corresponds to a halving time of 4.78 days. Data are from the Chinese Center for Disease Control and Prevention38, which includes cases diagnosed through Feb. 11. Not pictured: There is a drop in cases with onsets of symptoms after Feb. 538, likely due to many of those cases being diagnosed after Feb. 11. b The daily number of confirmed cases in Italy by date of symptom onset are shown as dots on a logarithmic scale (data are from Italian authorities47). The best ordinary least squares linear fits are shown as solid lines and have slopes (in units of day−1) of 0.262 (R2 = 0.927, 95% CI [0.202, 0.322]) for Feb. 16-25, 0.123 (R2 = 0.923, 95% CI [0.102, 0.144]) for Feb. 25 - Mar. 10, and  −0.068 (R2 = 0.901, 95% CI [−0.078, −0.058]) for Mar. 13 - Apr. 5. The change in the exponential growth rate from 0.262 to 0.123 likely occurred due to partial measures implemented by Italy, but it was not until a nationwide lockdown was implemented on March 9 that exponential growth changed to exponential decline. The rate of decline is much slower in Italy than in China, perhaps due to China’s stronger lockdown enforcement and contact tracing/quarantine measures.

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