The officials concluded the investigation into the recent COVID-19 outbreak at the Union Gap warehouse in Yakima County Tuesday saying that "is no current indication of ongoing transmission among employees."
The outbreak, which impacted 177 employees in total, "is considered to have concluded," health officials said.
Officials determined that the infections occurred over the course of nearly a month from Dec. 11 to Jan. 2. After the cases started to emerge, infected employees were forced to quarantine, the Yakima Health District and the store's general manager, Keri Luft, said.
Officials also advised Costco to conduct site-wide testing until the testing positivity rate was below 5%, according to officials.
The Yakima Health District began working with the wholesale club last month after 68 employees tested positive right before Christmas.
While investigating the surge in cases, Lilian Bravo, the director of Public Health Partnerships at the Yakima Health District, told FOX Business that Costco has followed all safety protocols and will be allowed to remain open.
The source of the outbreak was not identified, officials said. However, the health department said the "sharp increase in cases mimics the type of activity that happens after some sort of superspreader event." Officials were unable to pinpoint any specific event that may have caused the outbreak, Bravo said.
Luft also confirmed that the store did not hold an indoor or outdoor Christmas party.
Although the investigation has ended, Dr.Larry Jecha, Yakima Health District interim health officer, said it's a "stark reminder of how rapidly COVID-19 can spread throughout our community."
Jecha says residents must remain "vigilant and continue to take steps to minimize the spread of the virus" including wearing masks, practicing physical distancing, and avoiding large social gatherings.
Yakima County has seen a significant increase in COVID-19 cases over the last few weeks. To date, the county has reported more than 20,900 confirmed cases.
Despite this, health department officials have not recommended that any businesses close due to COVID-19 infection among its staff.