Del Mar Racetrack in California canceled this weekend’s horse racing after 15 jockeys and seven other track workers tested positive Tuesday for covid-19, the disease caused by the novel coronavirus.

Per the San Diego Union-Tribune, all but one of the people who tested positive spent the July 4 weekend working at Los Alamitos Race Course in Orange County, Calif. The summer racing meet at Del Mar, located north of San Diego, began July 10 without fans in attendance and will resume July 24.

“The good news is that all our jockeys and personnel who tested positive are showing no symptoms,” Del Mar chief operating officer Josh Rubinstein said. “If they are asymptomatic, they will be eligible to ride after 10 days.”

Victor Espinoza, who rode American Pharoah to the 2015 Triple Crown and was scheduled to race at Del Mar, already had tested positive for covid-19 on Friday. He, too, had raced at Los Alamitos. Another Del Mar jockey who had raced at Los Alamitos, Flavien Prat, tested positive Sunday, one day after riding at Keeneland in Kentucky. Those positive tests spurred Del Mar officials to test more than three dozen jockeys and track workers who had worked in proximity to them at Del Mar during its opening weekend.

In response, Del Mar has expanded covid-19 testing for backstretch workers and other personnel, expanded the jockeys’ quarters to allow for more social distancing and banned jockeys not based in California from racing for the remainder of the summer season. Plus, any jockey who leaves the track to race at other venues will not be allowed to return to Del Mar this summer.

Horse racing has been one of the few sports to remain operational during the novel coronavirus pandemic, with fans barred from the stands and preventive measures in place for workers. But this week has seen a number of jockeys test positive. Along with Espinoza and Prat, Luis Saez, Martin Garcia and Eduard Rojas Fernandez all tested positive after riding at Los Alamitos. So did Florent Geroux, who raced at both Keeneland and Belmont Park in New York last week. He told Thoroughbred Daily News that rules banning nonlocal jockeys from tracks might run into opposition if such a prohibition is in place for big races like the Kentucky Derby, which this year will be held Sept. 5.

“People are saying what about Saratoga, that Kentucky jocks or California jocks should not be allowed to go to Saratoga,” Geroux said. “Maybe not, but what do you for Derby week? Should only the regular jockeys in Kentucky be allowed to ride? We welcomed everybody at Churchill [during the spring meet] and all the jockeys from New York came there to ride. At Keeneland last weekend, all the jockeys from New York came to ride their big horses at Keeneland and no one put a stop on that. So why shouldn’t Kentucky and California jockeys be able to ride in Saratoga? If they can’t, only the Kentucky colony should be allowed to ride Derby week.”