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Boise State Public Radio News is here to keep you current on the news surrounding COVID-19, the disease caused by the novel coronavirus.

Blaine County Releases New 'Epi' Curve — Here's What It Shows

Courtesy of South Central Public Health District
An "epi" curve provides a moment-in-time look at the spread of illness within a community. This chart was captured by the South Central Public Health District on Sunday, April 12.

The South Central Public Health District released an epidemiological curve this week for Blaine County. It maps when people who've tested positive for coronavirus first started feeling sick.


“Epi” curves reveal time periods of when people might’ve been exposed and provide a general sense of the outbreak’s spread in a community.

This particular epi curve is from Sunday, April 12, which means illnesses reported since then are not reflected on the chart. 

“We can speculate a little bit through an epi curve that if we see a reduced amount of cases in a week and a reduce amount of onsets, that there’s not a lot of people ill in a community at that time," said Logan Hudson of the South Central Public Health District.

The public health district gathers the symptom onset information from individuals when it receives a person’s positive test result. Tracking symptoms like this is another way — in addition to looking at daily case numbers — for disease investigators to assess how well a population is flattening the curve

According to Blaine County’s epi curve, confirmed cases started having symptoms as early as March 1. The first case in the county wasn’t confirmed until two weeks later. The onset of symptoms peaked on March 13, when about 40 people in the county started feeling sick. Since then, it’s been trending downward, with occasional smaller spikes.

Hudson said it’s important to note that Epi curves can’t capture the picture perfectly when test results lag behind symptoms, Hudson said.

“Somebody that got sick yesterday and hasn’t gotten tested yet, we don’t know about it,” he said. 

So while the chart lists no confirmed cases whose symptoms began after April 4, there could be new cases who haven’t been tested or haven’t gotten results back, and therefore haven’t been contacted by the health department to report the day their symptoms started. It’s possible that those dates could fill in later on. 

In the past week, test results have started to come back within three days versus the 10 to 14 days it typically took before then. This gives epidemiologists a better understanding of the disease’s progression in a community at a given moment, Hudson said. 

In an interview with the Idaho Statesman on Tuesday, Dr. Kathryn Turner, Idaho’s deputy state epidemiologist, said the state may soon release a statewide epi curve.


Find reporter Rachel Cohen on Twitter @racheld_cohen


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