How do I know how much community transmission there is in my community? I am swimming in data! Someone throw me a rope!

Data and Metrics Data Literacy Infection and Spread

A: We recommend checking this awesome data exploration tool from Harvard University’s Global Health Institute.

We’ve talked a lot here at Dear Pandemic about how important community spread of COVID is, and how it’s necessary for anything like safe reopening in any setting–from first grades to zoos.
The map at the top of the Path to Zero site shows one of the best & most reliable measures of community spread (or, how much COVID is in your community): daily case incidence per 100,000 population. In plain English, that’s how many *new* COVID positive tests there are per day for every 100,000 people. Daily incidence is also averaged over the last 7 days to smooth out any weird daily fluctuations such as those that stem from slower test processing on weekends.

Below the map, there are some standards for deciding how much is “too much” COVID, developed by a team of A+ scientists. Their goal is “near zero” incidence–no new cases per day.
With that in mind, the team uses these cutoffs:

– less than 1 new case per 100,000 people per day is “on track for containment.”
– 1 to 9 new cases per 100,000 people per day is a medium risk, “community spread” category
– 10 to 24 new cases per 100,000 people per day is “accelerated spread”
– 25 or more new cases per 100,000 people per day is the highest risk category, which they title “tipping point” and recommend that stay-at-home orders should be implemented to slow the pandemic locally.

Some things that this measure is NOT: It is not the total cases so far, nor the currently hospitalized cases. It is not a percent of all tests that are returned positive, and it is not a percent of the population that is currently ill. Daily incidence, in public health terms, means the newly diagnosed cases each day.

We know this incidence per 100,000 people per day measure isn’t very intuitive, so here are two worked examples of this measure of the burden of disease:

1. Lafayette County, Florida had 175 new positive test results over the last 7 days combined. That’s an average of 25 new positives per day for the past week.
Lafayette County, Florida has a population of 8,422 people. 25 new positive cases daily / 8,422 people is a daily incidence of 0.002968 cases per person.
In order make that rate easier to read and compare to other places with very different population sizes, we multiply the per-person incidence by 100,000 people.
25 cases per day ÷ 8,422 x 100,000 = 297 new cases per 100,000 people, each day.
That falls well into the red zone–in fact, it’s the second highest daily incidence county in the nation.

2. The much larger Orange County, California has posted 2245 new cases in the last 7 days, for a daily average incidence of 320.7 daily cases. Orange County is home to 3,175,692 souls. To get the daily incidence per 100,000:
320.7 ÷ 3,175,692 x 100,000 = 10.1 new cases per 100,000 people each day. That falls in the orange zone.

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