PHILADELPHIA -- The Nationals-Phillies game scheduled for Wednesday at Citizens Bank Park was postponed to allow for continued testing and contact tracing involving members of the Nationals organization.

The teams will play a straight doubleheader on Thursday beginning at 12:05 p.m. ET. Tickets for Wednesday's game will not be valid for the doubleheader. Fans who purchased tickets (and parking) directly from the Phillies will automatically receive a credit to their account for the face value amount of each ticket. The credit can be used on tickets to any remaining Phillies home game this season, based on availability.

The postponement comes one day after Trea Turner departed Tuesday's game in the first inning after the team was informed that he had tested positive for COVID-19. Follow-up testing returned a total of 12 positive tests: four players (including Turner) and eight staff members.

"Some of the guys are asymptomatic, some are symptomatic," said manager Dave Martinez. "It's unfortunate this happened, but we've got to follow MLB protocols."

The Nationals reached the 85% vaccination threshold for lowered COVID-19 restrictions in late May. Martinez said the majority of the dozen who tested positive have been vaccinated.

"Thus far, nobody has gotten very sick, which is a good thing. I do believe the vaccinations have helped that in a big way," Martinez said. "Once again, I encourage people to get vaccinated. Like I said, it does help -- I'm seeing it firsthand. The guys that are getting sick, it's basically kind of a small head cold, but they're doing fine."

The four players who tested positive will not be available for at least Thursday's doubleheader. The organization is also undergoing further testing, and it expects to get another round of results prior to first pitch on Thursday.

Martinez said he will discuss roster additions with general manager Mike Rizzo when he gets back to his Philadelphia hotel on Wednesday night. Martinez has not decided on pitching plans for Thursday's two games.

Patrick Corbin was originally expected to start Wednesday's game, while the club was hopeful that Max Scherzer would return to the mound on Thursday after being scratched from Saturday's start due to right triceps discomfort.

"We're going to have to add [players]. That's something I'm going to talk to Mike about," Martinez said. "I'm sure I'll be talking to him all night long and try to figure out a roster for the next few days, and I'll also talk to [pitching coach Jim] Hickey about the rotation, then we'll go from there.

"Honestly, I haven't even thought about who's going to pitch or what. My concern is the health of everybody."

Scherzer was seen on the field, along with various other Nationals players, during Phillies batting practice prior to the game being postponed. However, a number of Washington players and staff members never emerged from the clubhouse and the team did not take batting practice after Philadelphia finished its round.

Martinez said he had the players who tested negative get on the bus and return to the hotel immediately following the decision to postpone the game.

"I'm just worried about the guys; I really am," Martinez said. "Like I said, it's been a tough go and this doesn't make it any easier. Hopefully, tomorrow's results, everyone comes back negative and we go back to playing baseball, which we all love to do. I hope everyone's OK."