I’m changing how I report the numbers of Covid-19 cases from daily reports to weekly ones.
During my working career I worked in animal disease outbreaks and eradication programs and, as in human disease outbreaks, we used different reporting cycles as the outbreaks progressed. Early on, case numbers were reported daily, as new cases were discovered showing the rapid movement of the disease. As a routine of testing and surveillance developed, the numbers got larger and reporting would change to weekly reports to reflect the weekly work cycle. In long term efforts, reporting might change to monthly or yearly reports to reflect the life cycle of the affected animals and seasonal effects.
With Covid-19 daily numbers can fluctuate due to more samples collected on some weekdays than others, reduced weekend schedules, etc. Looking at numbers on a weekly basis smooths out many of the differences and gives a better idea of increases, decreaes or plateaus. Sometimes the weekly reporting is done daily, counting the cases of the immediate past seven days; but I’m going to keep it simple and report each week as it ends on Saturdays.
I’ve started both charts from March 7, 2020 when the number of to-date reported cases totaled 336 in the US and 4 in Arizona. I could make a similar chart for Santa Cruz County which had 34 reported cases on May 2, but it would have little value as a predictor because a single household with a couple cases could skew the curve out of proportion to its import. Charts from counties with more cases might be useful.