Local outlet KOMO News reported all four individuals died Sunday after being hospitalized at the EvergreenHealth Medical Center in Kirkland, Washington.
Two of the four persons were residents of the senior home LifeCare and were reported as having underlying health conditions. Cases announced on Monday related to the state's King County and Snohomish County.
The latest development was announced at a news conference headed by Dr. Jeff Duchin, Washington's health officer for public health - Seattle & King County, where researchers stated that the virus had likely already been circulating undetected in the Evergreen State for weeks.
Prior to Monday's announcement, two other coronavirus-linked deaths had been confirmed by officials.
The latest figures collected by the Johns Hopkins Center for System Science and Engineering indicate that more than 89,000 COVID-19 cases have been confirmed by officials. Of those cases, 80,026 were recorded in mainland China. The US has more than 80 documented cases of the virus.
Globally, COVID-19 has claimed the lives of 3,048 individuals.