Positive results at the UW Medicine Virology Lab from outpatient and emergency room testing for COVID-19 began dropping after reaching a peak in late March.

The UW Medicine Virology lab, located in Seattle, along with colleagues from Fred Hutchinson Cancer Research Center, analyzed the positivity rates for specimens received from outpatient settings in 10 Washington state counties and in Seattle-area emergency departments. The patient samples were from March 1 to April 16. The peak in positive results occurred around March 28 to March 29.

The analysis is published Friday, May 8, 2020 in JAMA, the journal of the American Medical Association. See the paper here: https://jamanetwork.com/journals/jama/fullarticle/2766035

The senior author is Dr. Keith Jerome, professor and head of the Virology Division of the Department of Laboratory Medicine at the University of Washington School of Medicine. He is also a Fred Hutch infectious disease scientist.

Here’s more from the UW:

The UW Medicine Virology Lab began testing for Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) March 1. This new coronavirus is the cause of COVID-19. The UW Medicine Virology Lab was one of the first laboratories in the United States, outside of the Centers for Disease Control and Prevention, to conduct laboratory-based testing of clinician-submitted specimens for what became a pandemic virus.

Since March 1, the lab has tested samples from more than 95,000 patients in Seattle, other parts of Washington, and from around the United States. More than 90 percent of the samples came from the UW Medicine healthcare system and outreach clients from several areas in the state of Washington. Testing volumes steadily increased for the first half of March and peaked for outpatients around March 12 to March 13. Fewer samples were collected on weekends.

The researchers analyzed their collection of clinical result data from COVID-19 nasal swab testing to look for patterns in the pandemic affecting Seattle and parts of the state at large. They also wanted to determine the effects of public health mitigation measures, such as physical distancing.

There was only limited demographic information available on the patients testing. The researchers found that males had a higher positivity rate than did females. Positivity rates were higher from patient specimens taken in emergency departments. While emergency department and outpatient positive rates peaked about the same time, the decline in positive results was more gradual among populations seeking care in emergency departments.

The researchers noted this trajectory of peak and decline seems to align with the local physical distancing guidelines such as the March 16 statewide shutdown of restaurants and bars and social gathering limits, followed by the March 23 “Stay Home, Stay Healthy” order by Washington Gov. Jay Inslee.

Testing criteria did not change significantly over this study period, and remained largely limited to patients showing respiratory and other symptoms suggestive of COVID-19. Testing volume did not increase in the study population due to shortages of sample collection materials.

“The decline in positivity was not due to expanded testing,” Jerome explained.

These results, the researchers noted, suggest that the early and aggressive physical distancing measures enacted in Washington state have influenced the course of the COVID-19 pandemic in Seattle and other parts of the state.

Whether people’s adherence to physical distancing will continue, and how any changes in public behavior, such as the staggered reopening schedule of some public and commercial settings, might alter pandemic infection rates in the coming months remains to be seen.

The Department of Laboratory Medicine at the University of Washington School of Medicine and Fred Hutchinson Cancer Research Center funded this analysis.

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