Although rate is reflected differently, spread remains at elevated levels
FOR IMMEDIATE RELEASE:
2 February 2021
COLUMBIA, SC —The Department of Health and Environmental Management in South Carolina (DHEC) today announced a change in the way positive percentages are calculated for COVID-19 cases. With the change, South Carolina’s percentage positive calculations can be more easily compared to those used by federal entities, including the Centers for Disease Control and Prevention (CDC).
Start today, DHEC now reports percent positive using test-by-test method. The percentage positive is now calculated by dividing all positive COVID-19 tests by the total number of COVID-19 tests (positive and negative) and then multiplying the result by 100 to get a percentage.
With the change, the public is seeing a big drop in the number of positive percentages. This does not mean that the level of distribution in the community has decreased. Percentage seems to be positively lower because it is calculated differently.
DHEC will not only use this new method going forward, but it will also positively recalculate the percentage for the entire time that COVID-19 has been tracked in South Carolina. Anyone who wants to see what the old data looks like can visit this link: https://scdhec.gov/sites/default/files/media/document/COVID19-Archived-Percent-Positive.pdf.
State epidemiologist, dr. Linda Bell, said that it is important to note that you can not compare information from the old method (people above people) with the new method (tests on tests) if you change methods. ‘It is important that people understand that COVID-19, although seen as a positive number as a smaller number under the new way of calculating the rate, is still spreading at an increased level in our state. The smaller number is only based on the change in the way we calculate the rate, ‘said dr. Bell said.
‘It’s important that South Carolinians take the steps we know to protect us all from this deadly disease: wear a mask consistently and correctly, stay six feet away from others, wash your hands regularly and avoid crowds. And if your time comes, you must be vaccinated, ”said dr. Bell added.
New calculation allows for greater comparison of data
With many federal agencies and state health departments using the test-over-testing method, this change by DHEC will allow comparisons with percentage positivity calculations by the CDC, the White House Coronavirus Task Force, Centers for Medicare and Medicaid Services (CMS), others academic institutions and many states. In December, CMS began requiring healthcare facilities to use test-by-test; DHEC started preparing for the change at the time.
To understand how positive positivity is calculated
Previously, DHEC calculated percentage positively according to the method of people-over-tests. This requires that the number of people with positive results be divided by the number of people who have taken overall tests, which includes positive and negative results.
DHEC decided to use this method early in the pandemic because the focus was on identifying new people who tested positive. It becomes more difficult to do when many of the population have been tested. With the persistent recommendation that South Carolina be tested regularly, moving people to tests is also becoming a more effective method of monitoring active cases.
“The positivity rate helps public health officials to determine at what level COVID-19 is spreading in the community and whether enough tests are taking place,” said Dr. Bell said. “The tariff gives us a screenshot of how much COVID-19 is circulating in the community over a given period of time.”
What does percentage positivity tell us about the distribution of the community?
Percentage positive will be high if the number of positive tests is high, or if the number of total tests is low. A higher percentage positive indicates a higher prevalence and that there are likely to be more people with COVID-19 in the community who have not been tested.
Percentage positivity does not reflect a complete picture of COVID-19 in South Carolina. Although it tells us information about the spread of diseases, there are other factors at work as well, including access to testing and how quickly the results of the laboratory return. No single measure can give a complete picture of the distribution of COVID-19 in our state and our provinces.
For more information on COVID-19 percent positive rates in South Carolina, visit the testing tab on the dashboard at provincial level.