An outbreak of 77 positive COVID-19 cases has been traced to an illegal youth basketball tournament held last month in Rocklin, Santa Clara County public health officials said Friday.

Officials said the outbreak involving county residents includes 39 middle- and high school players, three coaches and 35 “additional contacts.” Those who tested positive are connected to a tournament Nov. 7-8 at Courtside Basketball Center in Placer County.

An additional 17 cases outside Santa Clara County also have been traced to the tournament, officials said in a news release.

“This outbreak is a troubling reminder that the widespread prevalence of COVID-19 in our community threatens all of us, and does not limit itself to geographic boundaries,” Dr. Monika Roy, Santa Clara County’s assistant public health officer,  said in a statement. “Public Health orders, directives, and guidance around contact sports and sporting events are in place for a reason. The risk of transmission in these settings can easily result in community spread that threatens the most vulnerable among us.”

County health officials said the tournament violated local and State orders for youth sports in effect at the time the outbreak began.

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“Unfortunately, Courtside Basketball Center has not been responsive to our outreach over many months,” Placer County’s interim health officer, Dr. Rob Oldham, told CNN recently.

The California Department of Public Health has initiated an enforcement investigation involving the tournament operator, according to the news release. Officials also said the youth basketball program hindered health officers’ ability to conduct a thorough investigation by failing to “timely and properly” report some of the initial positive cases among staff and players.

Courtside’s website said the center is closed until further notice “out of precaution with the statewide lockdown and for the safety of all.” It also said youth tournaments scheduled this weekend and next weekend have been canceled. Courtside’s owner could not immediately be reached Friday night.

Santa Clara County has some of the country’s strictest rules for contact sports. It recently banned professional, college and high school events within the county’s borders. That led the San Francisco 49ers to relocate to Arizona, Stanford’s football team to the Pacific Northwest and San Jose State’s team to Las Vegas. The county’s six Division 1 college basketball teams also have moved to locations where they can legally practice and play games.

The outbreak comes as California is seeing record numbers of cases during the holiday surge. Officials said in the news release that the outbreak from the youth sports event “is a stark reminder that failure to follow public health requirements can ignite chains of transmission that accelerate the spread of COVID-19 within the community.”

According to the news release, holding indoor games, players engaging in close-contact activities and the length of time they spent in close proximity during each game contributed to the high rate of transmission.

Officials added that state and local health orders prohibit any competition between youth teams, and any indoor youth athletic activity not involving masking and social distancing.

“As cases, hospitalizations, and ICU admissions continue to soar to record levels with no sign of slowing in Santa Clara County or across California, each of us must take every possible step to protect ourselves and our loved ones from transmission of COVID-19,” Public Health Officer Dr. Sara Cody said in a statement. “We risk continued, uncontrolled spread of the disease throughout our community and even more loss of life if we don’t each do absolutely everything we can to limit contact with anyone outside of our own household.”

Erica Pan, California’s acting State Health Officer, added in a statement that the situation involving the basketball tournament “is an example of people engaging in activities that put their friends and loved ones at great risk of serious illness and death.”

This is a breaking story. Check back for updates.