DES MOINES, Iowa - The Iowa Department of Public Health (IDPH) is now reporting positive and negative antigen test results following a steadily increasing volume of the rapid-result tests across the state.
While some states have chosen not to report antigen results, IDPH believes doing so will provide more complete information for Iowans. Updated data on coronavirus.iowa.gov now includes case counts for both PCR and antigen tests separately, and the combined total test results.
Antigen testing is a new type of COVID-19 diagnostic test that detects proteins on the surface of the virus and generates results faster than a PCR test, which detects the virus’s genetic material. PCR tests are considered the “gold standard” for clinical diagnosis of COVID-19, and is the test used by the State Hygienic Lab and Test Iowa.
On August 16, the CDC issued interim guidance for antigen testing, including regulatory requirements, collection and handling of specimens, and evaluation of results.
According to the CDC, the sensitivity of rapid antigen tests is generally lower than PCR tests, and clinical performance depends on the circumstances in which they are used. Antigen tests can be helpful for individuals tested in the early stages of infection when viral load is generally highest, or for known exposures to a confirmed case of COVID-19. They can also be used in high-risk congregate settings in which repeat testing could quickly identify positive cases to inform infection prevention and control measures, and prevent further transmission.
Currently in Iowa, antigen testing is being used in long-term care facilities, health care clinics, retail pharmacies and by a variety of other testing providers.
Antigen testing accounts for just 1.8% of all COVID-19 tests in Iowa at this time, but use of the test is increasing and expected to continue.
To date, antigen tests have been included in Iowa’s total case count, but individual test results have been classified as “inconclusive” rather than as positive or negative cases. Now that more is known about antigen tests, negative and positive results are now included in the state’s COVID-19 case reporting and calculation of positivity. The inclusion of antigen tests results in minimal change to the state’s positivity rate.
Public health has been conducting case investigations and contact tracing for all positive test results, including both antigen and PCR tests. All individuals who test positive by PCR or antigen testing continue to be directed to quarantine for 10 days from the start of symptoms, have symptoms improving, and be fever-free for 24 hours before returning to work, school or normal activities.
IDPH will continue to adjust its reporting to include new technologies, test types and information as the COVID-19 response evolves.