A COVID-19 outbreak at the Costco in Union Gap was at 176 staff members as of Tuesday, the Yakima Health District said.

The health district’s COVID-19 outbreak response team has been working with the store to monitor and address the outbreak, which is believed to have started before Christmas, when 68 workers tested positive for the virus.

Following health district recommendations, Costco will continue to offer sitewide testing of its employees on an ongoing basis until there is less than a 5% positivity rate, health officials said. A second round of testing began Monday.

Employees who test positive for COVID-19 are quarantining at home. The health district says precautions are in place, and people should wear a mask anytime they are in public and follow other health recommendations.

Local health officials have said they expected the Costco outbreak numbers to grow as more test results came back. They have said evidence indicates it resulted from a “super-spreader event,” in which multiple people were infected at the same time.

With the recent holidays and high community transmission, some of the newer cases among Costco staff may not stem from the outbreak there, said Melissa Sixberry, director of disease control at the health district.

“We anticipate with so much community transmission of COVID-19, and with the holidays that just passed, we’ll likely see more cases coming from Costco staff that may not necessarily be linked to the original outbreak,” Sixberry said in the update.

Costco has not responded to requests for comment from the Yakima Herald-Republic. The total number of employees at the wholesale store and service center is estimated at between 350 and 600, according to local business organizations.

Reach Tammy Ayer at tayer@yakimaherald.com or on Facebook.