Intended to supplement our Tuesday-Saturday daily reports, the Weekend Update provides details on where infected individuals contracted the virus, numbers of tests administered, and positive vs negative testing results in Snohomish County. This week we are also providing information on the number of new cases per 100,000 population, one of the key targets that Washington counties must meet to apply for Gov. Inslee’s Phase 2 reopening under the Safe Start Program.

Testing and contact tracing have been identified as key weapons in the battle with COVID-19, and having a plan to implement these at effective levels are among the criteria counties must meet to move to Phase 2 reopening. Knowing where the cases are is the first step; then through contact tracing individuals who come in close contact with known infected individuals can also be identified, tested and, if necessary, asked to quarantine.

The criterion getting the most attention however is the incidence of new cases. Originally set at 10 or fewer new cases per 100,000 population, it has recently been relaxed to 25 cases per 100,000 (see the updated list of criteria from the Governor’s Office here.

As announced Friday, Snohomish County plans to submit its application for Phase 2 reopening on Monday, and despite still being just short of the target, the new standard will certainly make its case stronger. (Note that the chart provided Saturday tracing this metric comes from the Snohomish Health District and was made prior to this weekend’s announcement of the relaxed standard, hence the target line still indicates the old standard of 10 cases per 100,000).

Weekly test numbers are presented in two ways: broken out by week (red and green bars), and cumulative over the full reporting period (yellow and green bars). The weekly numbers chart shows a steady rate of testing, with between 2,500 and 3,500 tests administered countywide each week (note that data for the most recent week, 5/19-25, is incomplete, and will be updated in the next report). Notably, the proportion of positive results has been decreasing steadily over the reporting period. The cumulative testing chart reflects this, showing steady growth in the pool of tested individuals and a predominance of negative results.

To date, 32,659 tests have been conducted in Snohomish County (3.97% of the total population of 822,083), of which 96% (29,751) were negative and 4% (2,908) were positive. For comparison, the latest data on statewide testing from the Washington State Department of Health COVID-19 Information website reports 348,243 Washingtonians have been tested to date (3.95% of the total population of 7.8 million), of which 94% (327,162) were negative and 6% (21,071) positive.

The Source of Exposure chart displays the history over the past two weeks on how Snohomish County COVID victims acquired the virus. According to these data, community transmission (going to stores, gathering in groups, touching surfaces containing virus particles, failing to maintain recommended social distancing, etc.) continues to be the overwhelming source of infection. The message: wearing masks, social distancing and not gathering in large groups continue to be the most effective strategies to slow the spread of COVID-19, and will be an important part of a successful transition to Phase 2.

— By Larry Vogel