The case definition was an increase in the mean of expected cases, between two consecutive weeks, equal or higher than twenty percent \(\left(r\le\frac{1}{1.2}\right)\). For sensitivity analysis, the detection of an increase in the mean of expected cases equal or higher than 50 percent\(\left(r\le\frac{1}{1.5}\right)\)was considered. Data were analyzed separately for each country and for each of the states of the United States of America that had experienced a total number of cases higher than 20,000, until April 13, 2021.