Figure 5. Distributions of Ct values and Rt
We analyzed the association between Ct values and number of new cases and between Rt and number of new cases. Both Ct values and Rt rose before a surge in new cases, so we analyzed the association in consideration of a time lag.
We performed a regression analysis to examine the association between daily Ct values and incidence per million population, and the time lag at which the two variables were most strongly correlated was 7 days. Thus, we analyzed the association between Ct values and incidence per million population seven days later, and the results confirmed a negative association between Ct values and number of new cases, where new cases decreased with increasing Ct values (Figure 6).