We undertook a cohort investigation of OHCA attended by emergency medical services (EMS) in Seattle and King County, WA from January 1 to April 15, 2020. Patients where EMS attempted resuscitation (EMS treated) and where EMS responded but did not provide resuscitation because of signs of irreversible death (dead on EMS arrival) were included. Our population-based OHCA registry systematically abstracts information about OHCA presentation, treatment, and outcome from dispatch audio recordings, defibrillator electronic data, prehospital and hospital records, death certificates, and medical examiner reports, organized according to the Utstein template.

In this region of 2.2 million persons, EMS is a two-tiered system, administered by Public Health–Seattle & King County, enabling direct engagement for comprehensive disease surveillance. The study was approved by the University of Washington Institutional Review Board.

We undertook a hierarchical COVID-19 classification strategy that prioritized polymerase chain reaction (PCR) testing obtained pre or post mortem and clinical classification of a COVID-like illness (CLI) if PCR testing was not performed. Beginning in March, the medical examiner prioritized lab testing in decedents with an uncertain cause of death or respiratory symptoms prior to death. To identify patients with lab-confirmed COVID-19, we linked the State’s COVID-19 surveillance system to EMS electronic records.

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