Rate of spread
Rate of spread
For Official Merced County Data:
The rate of spread of COVID-19 in Merced County has gone through 4 phases so far. Each phase is marked by straight-line trend when the vertical axis is plotted on a logarithmic scale, which indicates that these are exponential growth patterns. The slope of the straightline indicates the daily growth rate and is reported in th etable below. The time to double number of cases approximately equals 70 divided by the growth rate.
In the State of California, a county is flagged for elevated disease transmission criteria if (CDPH):
The 14-day increase in positive cases per 100,000 is above 100, OR
The 14-day increase in positive cases per 100,000 is above 25 AND the 7-day testing positivity exceeds 8.0%
Click here for more on the methods used to produce these figures.
For reasons I have not been able to fully understand, the official 7-day test positivity is significantly below the values calculated here. See an example of the method used here below.
On July 21, 22,173 tests and 2,813 positives were reported. On July 28, these increased to 24,640 and 3,763, respectively. In a span of seven days 2,467 new tests and 950 new positive cases were reported, which translates to 38.5% of positivity.
This calculation does not account for delays between sample collection and reporting of test results. Nevertheless, the effect of delayed is likely to be minor because the daily number of tests remained roughly constant at ~350 tests/day since early June (see the data of test results below).