Brooks Koepka and Webb Simpson, two of the top five golfers in the world, were among five players who withdrew from the Travelers Championship, four of them out of a chain-reaction abundance of caution as the coronavirus put the PGA Tour on notice.

"The snowball is getting a little bit bigger," Graeme McDowell said after withdrawing because his longtime caddie, Ken Comboy, tested positive for the virus.

The tour released results that showed three positive tests at the TPC River Highlands in Connecticut — Cameron Champ and the caddies for Koepka (Ricky Elliott) and McDowell. Koepka's brother, Chase Koepka, also withdrew because he had been in contact with Elliott. Chase Koepka had made the field through the Monday qualifier.

Simpson, who won the RBC Heritage last week with a record score that moved him to No. 5 in the world, withdrew when he learned a family member had tested positive.

As it enters the third week in its return from the pandemic that shut down golf for three months, the tour has administered 2,757 tests at PGA Tour and Korn Ferry Tour events in five states, with seven positive results. Nick Watney was the first player to test positive, last week at the RBC Heritage in South Carolina.

"It's a low number on a percentage basis, but every number hurts," PGA Tour Commissioner Jay Monahan said. "I think we all need to remind ourselves that we're all learning to live with this virus.

"It's pretty clear that this virus isn't going anywhere."

Monahan said the tour would continue, and he said there was no set number of positive tests that would lead to golf shutting down again.

Monahan sent a memo to players that outlined increased measures in its health and safety protocols. Those include testing players before and after they take charter flights. Swing coaches now face mandatory testing each week and will be considered part of the bubble, and the fitness trailer will be at tournaments to keep players from going to gyms.

He also said the tour will no longer pay for players or caddies to be in isolation for positive tests if they have not followed the health and safety plan.

"All of us have an extraordinary responsibility to follow these protocols," Monahan said, adding he has been guilty at times as he adjusts to a new way of living. "For any individual that does not, there will be serious repercussions."

After four positive tests in six days, Monahan said no one should be surprised if there are more next week in Detroit.

"I'm certainly hopeful we won't," he said. "But to be able to say that we're going to not have any cases ... would be disingenuous because we're all learning as we're going."

Koepka said Elliott tested positive and then took another test that came back negative. No matter. Koepka chose to withdraw, and was especially gutted that his younger brother withdrew after earning a rare chance to play.

"I feel terrible for Chase," Koepka said. "It's one thing if I withdraw. He doesn't get this opportunity very often."

McDowell said his caddie flew on a packed commercial flight from Dallas to Orlando after he missed the cut at Colonial. That Monday, they went to a memorial service — along with Elliott, who grew up with McDowell in Northern Ireland, and McDowell's trainer — and then they all drove six hours to Hilton Head.

"The problem is, people are out here passing tests when they could still have the virus," McDowell said. "That's what we're learning. Ricky passed a test on Monday and he just failed it this morning."

Blackmon is a first

Colorado All-Star outfielder Charlie Blackmon became the first Major League Baseball player known to have tested positive for the coronavirus. The Denver Post said he was among three Rockies players to test positive but did not identify the others. Several other MLB teams have acknowledged positive tests but have not identified the players involved.

NBA players positive

Indiana's Malcolm Brogdon and Sacramento's Jabari Parker and Alex Len revealed they had tested positive for the coronavirus.

All three said in statements they expect to be with their teams when the NBA season resumes at the Disney complex near Orlando next month.

All 22 NBA teams that will be part of the resumed season began testing Tuesday. League officials have said positive tests are inevitable. The hope is that testing now will reveal cases and position players to recover before games start July 30.

Team quarantined

Grand Canyon's entire men's basketball team was placed in quarantine after four players and two support staff members tested positive for COVID-19.

All 14 players and two student managers will stay at a designated on-campus residence hall for the next two weeks.

Rapids have case

The Colorado Rapids of Major League Soccer said one player tested positive for COVID-19. The club suspended training to conduct more testing and also began contact tracing.