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Positivity rate, not number of tests, tells us if disease is spreading.

Positivity rate is a metric we watch closely. It helps us gauge how widespread COVID-19 is in the community. To understand this number, we need to know about the number of tests conducted.

We averaged more than 1,200 people getting COVID-19 tests per day since the second week of July. Two weeks earlier, we averaged about 1,000 tests per day. During the second week of June, about two months ago, we averaged only 570 tests per day. We are doing about double the amount of testing from two months ago.


The large increase in tests processed is good news. It is not near where we need to be to reach the state’s Safe Start metric. But it is a big improvement. Our numbers also show people get a COVID-19 test within 2 days of becoming ill and most (but not all) get their results within 4 days. We added an indicator on our Safe Start dashboard today to show how quickly the health department learns about positive test results.

If the number of tests stays the same, then an increase in cases means an increase in disease spread. When the number of tests increases, we need to calculate the positivity rate to know if the disease is spreading. The positivity rate compares the number of positive cases to the number of tests. When disease spreads, the positivity rate increases. When disease is contained, the positivity rate stays flat or declines—even if testing increases.

In Pierce County, the positivity rate has been steadily increasing since May. In May we tested about 500 people per day and about 10 of them were positive. This is 2 positive cases for every 100 people we tested. In the third week of July, each day we tested about 1,300 people and about 90 were positive. This is 7 positive cases for every 100 people tested. In the first full week in August, each day we tested about 1,200 people and about 70 were positive. This is about 6 positive cases for every 100 people tested.

So COVID-19 is spreading in our community. Most recently, it looks like we may be seeing a decline in the positivity rate. That will be an important sign that things are starting to get better. But it isn’t a reason to relax. Continue to maintain social distances. Wear your masks, and avoid indoor spaces.

More to do.

We have a long way to go before we fully understand COVID-19. We don’t know how common long-term complications are. Are they permanent? Will they just go away? It’s still too early to tell. We need more research.

Meanwhile, you can take simple steps to protect yourself and people you care about:

  • Wear a mask when you leave home. No shirt, no shoes, no mask? No service.
  • Limit your interactions to a small circle of friends and family.
  • Stay close to home.
  • Keep gatherings small and outside if possible.
  • Fresh air and physical distance help keep you safe.
  • Wash your hands, cover your cough, and keep up your best hygiene and sanitation.
  • Get tested if:
    • You think you were exposed.
    • You are a member of a heavily impacted community – Native Hawaiian, Pacific Islander, Latinx, Black or African American, American Indian, Alaska Native.
    • You have been in large gatherings of any sort.
    • You are experiencing symptoms.

To see overall COVID-19 testing numbers for Pierce County, see the testing tabs on the Safe Start dashboard at