The SCAN study has tested 5,610 individuals for the virus that causes COVID-19 between its re-launch on June 10th and July 28th, returning 79 positive test results. Since the program first began testing on March 23rd, SCAN has tested a total of 17,957 individuals, identifying a total of 180 positive cases across King County.

SCAN is a public health surveillance program for infection from SARS-CoV-2—the virus that causes COVID-19—that offers free testing of home-collected samples in greater Seattle and King County. The study is designed to help understand the COVID-19 outbreak more completely and, together with other data sources, inform public health decisions.

SCAN’s latest technical report contains several findings with implications for King County’s response to the ongoing pandemic. In summary:

1. Although SCAN participants who report having known or suspected contact with someone infected with COVID-19 have a higher risk of testing positive, a large proportion of SCAN participants who test positive for COVID-19 report that they are unaware of having recently been in close contact with someone who tested positive for the virus.
2. Participants who report symptoms of COVID-like illness are more likely to test positive. Acute loss of sense of smell or taste (anosmia) is the strongest single predictor of COVID-19 infection in our data.
3. Individuals can identify their own risk of contracting COVID-19 through their awareness of contact exposure and symptoms, and should seek testing or contact their healthcare provider if they self-identify as being at risk.
4. Improvements in SCAN’s delivery and lab processing logistics have reduced the average time between enrollment in SCAN and return of results to about 48 hours. The largest delay involves people waiting to test after symptom onset. Getting tested soon after onset of symptoms and suspicion of illness is critical to interrupting the chain of COVID-19 transmission.
5. While mask usage has increased over time, rates appears to be stalling below universal compliance. Trading social distancing for mask use is counterproductive for COVID-19 prevention. The best way to protect each other when we must go out is to maintain at least six feet of distance from others and to always wear a mask.
6. Use of SCAN codes, which allow individuals who meet certain criteria to bypass the normal screening process and automatically receive a SCAN test kit, has helped to facilitate greater participation of children and high-risk cases in SCAN.

You can find additional information on each of these summary findings below:

1. Although SCAN participants who report having known or suspected contact with someone infected with COVID-19 have a higher risk of testing positive, a large proportion of SCAN participants who test positive for COVID-19 report that they are unaware of having recently been in close contact with someone who tested positive for the virus.

Among SCAN’s 5,610 participants between June 10th and July 28th, 80% (4,476 people) reported no recent contact with an individual known or suspected to be infected with COVID-19. Of those reporting no recent contact, 0.7% (33 of 4,476 people) tested positive, compared with 7.2% (33 of 457 people) who tested positive and reported having known contact with a positive case, and 1.6% (12 of 721 people) who tested positive and had suspected contact with an infected individual.

Based on these results, SCAN study participants who reported coming into close contact with a person they knew was positive for COVID-19 (defined in this report as being less than six feet apart for at least 10 minutes) were 10.8 times more likely to test positive for the disease relative to those with no recent reported contact. Participants who suspected that they might have come in close contact with an infected individual were 2.4 times more likely to test positive than those with no recent contact.

When comparing participants who reported close contact with friends, co-workers, and household members, positivity rates were highest for those in contact with COVID-positive household members, since these interactions are more likely to be prolonged, closer, and take place indoors.

While having known or suspected contact with COVID-19 increases the risk of having the disease, SCAN’s results show that many individuals tested positive despite not knowing or suspecting that they had come into close contact with the virus. This highlights how important it is to decrease activities outside the home, maintain six feet or more of physical distance from others, and wear a mask when in public —even in the absence of known risks—to prevent both transmitting and acquiring COVID-19.

“The fact that many who test positive for COVID-19 are unaware they came into contact with an infected individual underscores how important it is to decrease activities outside of the home, maintain six feet of distance with others and wear a mask whenever in public,” said Dr. Jeff Duchin, Health Officer for Public Health – Seattle & King County. “This is also a clear call to action for those who suspect or know they are infected to quickly tell their recent contacts they may have been exposed. Rapid action by everyone in the community to identify and prevent exposure is how we break the chain of transmission.”

2. Participants who report symptoms of COVID-like illness are more likely to test positive. Acute loss of sense of smell or taste (anosmia) is the strongest single predictor of COVID-19 infection in our data.

Since June 10th, 1.5% of SCAN participants (61 of 4,045 people) who reported COVID-like illness (CLI) upon screening for enrollment tested positive for the disease. Only 0.1% (1 of 921 people) of participants who did not report CLI tested positive.

Reinforcing findings from other research on the topic, SCAN found that anosmia (loss of smell or taste) is the most predictive single symptom for infection. Anosmia is rare in the general population compared to other symptoms, but among SCAN participants between March 23rd through July 28th reporting anosmia, 8.4% were positive for COVID-19 infection. Other symptoms related to testing positive included eye pain (3.7% reporting the symptom tested positive), feeling feverish (3.3%), chills or shivering (3.2%), sweats (2.9%), and muscle aches/myalgia (2.3%). It is important to remember that these are symptoms reported at the time of testing and other symptoms may have developed after that time.

Although asymptomatic infections occur at a lower frequency, research suggests that viral load and transmissibility of COVID-19 is highest at symptom onset, and identification of potential infections through symptoms remains a key tool in preventing the spread of COVID-19.

3. Individuals can identify their own risk of contracting COVID-19 through their awareness of contact exposure and symptoms, and should seek testing or contact their healthcare provider if they self-identify as being at risk.

SCAN’s findings suggest that individual knowledge of one’s own risk can indicate COVID-19 presence. Individual awareness of COVID-like symptoms and contact exposure is critically important to guide individual behaviors—including immediate testing, self-isolation, and informing contacts about potential exposure—that will help to prevent further spread of the virus.

Free COVID-19 testing is available at locations throughout King County, regardless of immigration or insurance status. Please be aware that increased demand for testing may lead to unexpected delays and wait times. At most locations, people who are experiencing symptoms or have had exposure to a known positive will receive priority, including when enrolling in SCAN.

4. Improvements in SCAN’s delivery and lab processing logistics have reduced the average time between enrollment in SCAN and return of results to about 48 hours. The largest delay involves people waiting to test after symptom onset. Getting tested soon after onset of symptoms and suspicion of illness is critical to interrupting the chain of COVID-19 transmission.

The latency between when a participant enrolls in SCAN and when they receive their test results has improved since SCAN first launched on March 23rd, and now takes an average of about 48 hours. Recent changes to enrollment procedures are expected to shorten this time period further. However, the largest latency is currently between symptom onset for an individual and when they make the decision to enroll in SCAN, at an average of 3.5 days and varying between one and 15 days.

Reducing the time between infection/symptom onset and testing is critical to inform individuals and their contacts about their status and potential exposure to COVID-19 in order to prevent further spread of the infection.

5. While mask usage has increased over time, rates appears to be stalling below universal compliance. Trading social distancing for mask use is counterproductive for COVID-19 prevention. The best way to protect each other when we must go out is to maintain at least six feet of distance from others and to always wear a mask.

Since May 8th, SCAN has collected voluntary responses from website visitors not participating in SCAN on that given day, by hosting an additional survey that operates outside of testing enrollment windows. The survey is a simple convenience sample of website visitors and is not sampled for representativeness, and is not linked to individual lab results like the rest of SCAN’s participant questionnaire data.

Combining results from this voluntary website survey and SCAN’s participant questionnaire for a total sample of 19,430 responses, self-reported mask usage (those who report always wearing masks) has increased from about 50% in early May to about 90% as of July 28th. This contrasts with a concurrent reduction in those reporting social distancing of at least six feet from non-household members, with data suggesting that about 40% of the population has traded one risk reduction strategy for the other.

While wearing a mask helps to protect from COVID-19 infection, it is far from perfect alone and should not be relied on to prevent transmission. Reducing activities outside the home and practicing physical distancing are the most important preventative steps that individuals can take to reduce the spread of COVID-19, along with masking whenever in public.

6. Use of SCAN codes, which allow individuals who meet certain criteria to bypass the normal screening process and automatically receive a SCAN test kit, has helped to facilitate greater participation of children and high-risk cases in SCAN.

In June and July, SCAN has increasingly provided direct enrollment codes to individuals for several reasons: for those attending protests; to increase testing in children; in collaboration with community-based organizations to improve access to testing; and for SCAN participants who test positive to share with their close contacts.

Of the 5,610 individuals that SCAN tested between June 10th and July 28th, 664 enrolled using priority codes. 2.6% of those who enrolled in SCAN using priority codes—a total of 17 individuals—tested positive for SARS-CoV-2.

The SCAN (the greater Seattle Coronavirus Assessment Network) study is a research study conducted by the team behind the Seattle Flu Study, in association with 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 assistance from the Bill & Melinda Gates Foundation and the Centers for Disease Control and Prevention.