LAS VEGAS (AP) — One Las Vegas Strip resort said Thursday that it tallied 548 positive tests for COVID-19 among its 12,000 employees since May.

Wynn Resorts reported that testing found 51 positive cases of the new coronavirus among returning workers before the hotel and casino reopened June 4, and 497 since then.

In a statement, company CEO Matt Maddox said a 10-person full-time contact tracing team determined that 98% of those who tested positive contracted the virus outside of work.

Six guests have tested positive among more than 500,000 who have stayed at the 2,700-room Wynn Las Vegas and 2,000-room Encore since they reopened, the company said. Guests who self-identify with potential exposure to the virus or display symptoms are offered in-room testing.

More than 15,000 employee tests have been conducted, and the 548 positive results amount to a positivity test rate of 3.6%, which the company noted was below the U.S. national average.

The COVID Tracking Project on Tuesday put the 7-day rolling positivity rate for testing nationally at 5.4%.

Tests last Friday found just one positive result among 285 employees, Wynn Resorts said.

Most Las Vegas casino owners do not make coronavirus testing data public.

About 85% of COVID-19 cases in Nevada have been in the Las Vegas area, home to more than two-thirds of the state population.

The Southern Nevada Health District on Thursday reported 63,301 cases of COVID-19 in Clark County since the pandemic began, and 1,309 deaths.

Statewide, the number of confirmed COVID-19 cases is nearly 75,000, and the number of deaths has topped 1,500.

For most people, the virus causes mild or moderate symptoms, such as fever and cough that clear up in two to three weeks. Some, especially older adults and people with existing health problems, can experience more severe illness including pneumonia and death.