On March 23, Public Health — Seattle & King County and the team behind the Seattle Flu Study launched the greater Seattle Coronavirus Assessment Network—or SCAN for short. Thanks to the participation of volunteers across the county, SCAN has already begun to identify cases that might otherwise have gone undetected.

In its first 18 days, SCAN tested 4,092 samples. Nearly two-thirds of those were returned by individuals who in the seven days prior to enrollment had reported COVID-like illness (fever, cough, or shortness of breath). However, more than three-quarters of these individuals indicated they had not yet sought medical care. SCAN is the first COVID-19 surveillance program in the U.S. to use “swab-and-send” test kits that allow individuals to collect their own nasal sample and return it to a lab for testing without leaving home—while observing physical distancing guidance and reducing exposure to others.

SCAN testing among those reporting COVID-like illness (CLI) returned 44 (1.6%) positive results for COVID-19—a proportion lower than that being returned through testing within the medical system, but one that may still represent thousands of unrecognized infections in the community.

Cases were identified in all parts of King County. Based on this participant and county census data, SCAN modeling estimates that community prevalence of COVID-19 for the period is between 5 and 75 out of 10,000 people (0.05% to 0.75%), with best estimate of 24 per 10,000 (0.24%).

This early sample shows that community prevalence is around 0.32% (and ranging from 0.08% to 1.18%) during the first six days of testing and 0.07% (and ranging from 0.01% to 0.36%) in the last six. Although the trend is decreasing, the team cautions that the conclusion is uncertain and not statistically significant given the sample size. We are also still learning about the population represented in SCAN and it is too early to draw general conclusions from the data.

According to Jay Shendure, Scientific Director of the Brotman Baty Institute and SCAN’s lead partner, the team has been highly encouraged by the community’s interest in SCAN. “We’re working quickly to make kits available to even more people over the coming weeks, he said, “and to get data into the hands of the public officials who need it.”

“SCAN has already described a meaningful part of the iceberg,” added Dr. Thomas Lynch, president and director of the Fred Hutchinson Cancer Research Center, a key partner in SCAN. “This first-of-its kind’ infection surveillance platform is not only helping public health officials better understand and respond to the outbreak—it is also expanding access to testing within our community.”

More is being done to increase the demographic and geographic distribution of those participating in the program, however. The team is in particular encouraging more parents to enroll their children (under the age of 18). Seattle Children’s is assisting SCAN’s efforts in pediatric testing and emphasized that although there has been a lower case-rate among children to date, understanding transmission among young people is critical to the community’s response.

“COVID-19 seems to occur with mild or even no symptoms more often among children than in other populations,” said Seattle Children’s Chief Executive Officer Dr. Jeff Sperring. “As a result, the number of pediatric cases going undetected in our community may be even higher than we realize. As the only platform currently offering testing to people not reporting COVID-like illness, SCAN is a critical resource for helping us learn more about COVID-19 among young people.”

SCAN is also working to increase representation among residents 65 and older and within the south and east regions of King County. In the coming weeks, SCAN will be made available in eleven additional languages, with Simplified Chinese, Spanish, and Vietnamese launching the week of April 20. Right now, men are also underrepresented, as are individuals in essential occupations—such as transportation workers and grocery clerks—and their families.

Dr. Jeff Duchin, Health Officer for Public Health — Seattle & King County, emphasized the importance of efforts to ensure greater diversity among SCAN participants. Noting that demand for the SCAN swab kits has consistently outstripped supply for the past three weeks, he encouraged people to keep trying. “SCAN is a way for King County residents to help us better understand the true extent of the outbreak,” he said. “As more representative samples from people all across the region are collected and tested, the findings will become increasingly valuable.”

Dr. Paul Ramsey, CEO of UW Medicine, agreed, adding that SCAN’s value also has the potential to make a difference far beyond King County. “What began as a small, local pilot program has become a model from which we hope other cities and states will benefit. It’s a powerful testament to the accomplishments of our region’s world-class health and research community.”

Questions and answers about the SCAN data report

Where is COVID-19 in our community right now? Is it more prevalent in some regions than others?

SCAN testing for the period between March 23 and April 9 identified cases of COVID-19 in most regions of King County. It is too early to tell based on these data if there are ‘hot spots,’ but it is clear that the virus is present throughout the county, and consistent with current COVID-19 case report mapping by Public Health. We’ll learn more as we collect additional data over the coming weeks.



SCAN testing for the period between March 23 and April 9 identified cases of COVID-19 in most regions of King County. It is too early to tell based on these data if there are ‘hot spots,’ but it is clear that the virus is present throughout the county, and consistent with current COVID-19 case report mapping by Public Health. We’ll learn more as we collect additional data over the coming weeks. How many people tested positive who were not experiencing COVID-like illness?

In the first 18 days of SCAN testing, all cases of COVID-19 were among individuals who in the previous seven days reported symptoms compatible with COVID-like illness (cough, fever, shortness of breath). It should be noted, however, that because the total number of samples tested is still relatively low, additional testing is needed to estimate the potential number of asymptomatic or pre-symptomatic coronavirus cases in King County. Some people with the virus may have other symptoms, and not develop cough, fever, or shortness of breath. We need more data to understand this better.

I have not been able to get a test kit. What can I do? Currently, we can send, receive, and test a limited number of swab kits each day. Due to a high level of interest from the community, we run out quickly. We appreciate your patience and encourage you to keep trying. Please remember, however: SCAN is an infection surveillance program and not a clinical service. If you don’t feel well or suspect you might have COVID-19, stay home, contact your healthcare provider, and follow public health guidance

In which languages will SCAN be available, and when will they launch?

SCAN will be available in eleven languages, in addition to English. Spanish, Simplified Chinese, and Vietnamese will launch the week of April 20. Amharic, Traditional Chinese, Korean, Russian, Somali, Tagalog, Tigrinya, and Urdu will follow at a later date.

When will the next SCAN data report be made available and how often will it be published?

The next SCAN update will be on Friday, May 1, with additional reports published every two weeks thereafter.

About SCAN

SCAN is a partnership between the team behind the Seattle Flu Study and Public Health — Seattle & King County. It is executed by the Brotman Baty Institute, a collaboration between UW Medicine, Fred Hutchinson Cancer Research Center, and Seattle Children’s. SCAN relies on data modeling support from the Institute for Disease Modeling (IDM). It is funded by Gates Ventures (the private office of Bill Gates) and receives technical guidance from the Bill & Melinda Gates Foundation and the Centers for Disease Control and Prevention.

Originally posted 4/17/20