CLEVELAND — A terrifying word circulated Tuesday at the Republican National Convention: norovirus.

A dozen staffers in the California delegation who had arrived in Cleveland early had fallen ill with the extremely contagious virus, California GOP chairman Jim Brulte said Tuesday.

The virus causes extreme vomiting and diarrhea and has been known to spread explosively through people in closed places, such as cruise ships, schools and nursing homes, according to the Centers for Disease Control and Prevention.

By Wednesday, it was official: Test results showed 13 Californians supporting the delegation had norovirus, Erie County health officials announced. There have been no new cases since Tuesday afternoon, which is "a very good sign," said County Health Commissioner Pete Schade.

"After you start feeling better, you still have a couple days where you have to be really careful that you’re not transmitting the virus," Schade said. He expects that, as long as there are no additional cases into Thursday afternoon, the outbreak may have been beaten.

Brulte said that, so far, no delegates or alternates have shown symptoms. He said his delegation will continue to attend the convention at Quicken Loans Arena, where the Californians sit next to the Maryland delegation.

The delegates from California are staying at the Kalahari Resort in Sandusky, Ohio, nearly 60 miles away from Cleveland. Brulte said the delegates and their guests were spending the day Tuesday at the Cedar Point amusement park in Sandusky or at the Pro Football Hall of Fame in Canton, Ohio — or just relaxing at the Kalahari Resort.

Brulte said he believes one staffer brought the virus to Ohio from California and then passed it to the staffer's spouse. (County health officials also suspect that those who first became ill with the virus contracted it out of state).

The infected individuals first began showing symptoms Thursday, the Plain Dealer reported. By Monday, 11 visitors at the resort had become ill, with symptoms including fever, vomiting and diarrhea, according to the health department.

Then on Tuesday, 12 of the 36 staffers were sick.

State party officials alerted the delegation Monday morning to the norovirus outbreak and briefed attendees again Tuesday. They also informed Ohio health officials Monday, according to the Erie County Health Department.

"We will continue to follow all county health department directives to keep the illness from spreading. We wish our staffers a speedy recovery," Kaitlyn MacGregor, communications director of the California GOP, said in an email to The Post.

They have instructed delegates to wash their hands frequently, use sanitizers, and avoid shaking hands (something, as it happens, that Donald Trump has long been loath to do). They also should not share food and have been told to stay off delegation buses to the convention arena if they exhibit any symptoms of norovrius.

"I applaud those folks out there," Schade, the health commissioner, said. "They've been laying low and doing everything we've asked them to do."

The Centers for Disease Control and Prevention (CDC) explains how the norovirus stomach bug spreads and how you can protect yourself from getting it. (The Centers for Disease Control and Prevention (CDC))

The virus can be caught through contact from infected people or surfaces, or through consuming contaminated food or water. Norovirus inflames the stomach, the intestines, or both. Symptoms include stomach pain, nausea, diarrhea and vomiting. Such symptoms can be especially dangerous for young children and older adults.

Every year, about 19 to 21 million people become sick with norovirus; about 570 to 800 people die annually from it, according to the CDC.

In Ohio, hand-sanitizer dispensers were spotted Monday night at the resort where the California delegates are staying, the Los Angeles Times reported.

"We worked with the hotel to add sanitizing stations in and around the area where our delegation activities are," Brulte said.

The African-themed Kalahari Resort in Sandusky has 884 guest rooms, according to a company website. The property features indoor and outdoor water parks and an outdoor adventure park.

A spokeswoman for Kalahari Resorts said the company is cooperating "with all necessary officials."

"In preparation for the Republican California Delegates' stay, Kalahari Resorts and Conventions worked diligently with government officials to ensure we exceeded all health and sanitation requirements and protocols," spokeswoman Samantha Flynn said in a statement. "This includes passing extensive testing prior to, and continuing through, the delegation's visit."

Public health workers investigated the resort, including its food preparation areas, and found no issues "that warranted any corrective action," a from the county health department statement reads.

The California delegation includes 172 delegates and 168 alternates, plus a number of guests, with the entire group numbering about 500, Brulte said.

Of the ailing staffers, Brulte said, "Most of them are disappointed they can't work, but they understand that they're out of circulation" until they are symptom-free for at least 24 hours.

"We're in touch with the California delegation about this," said Audrey Scagnelli, spokeswoman for the RNC. "They're working with local health officials and are taking all the necessary precautions to contain the virus. We'll continue to monitor the situation and ensure the delegation and staff have everything they need."

News reports of the California delegation's remote accommodations in Sandusky surfaced earlier this year, when state GOP leaders complained that they were being put up so far from the convention site.

The complaints prompted convention organizers to bristle at suggestions they had dropped the ball on accommodating the GOP's largest delegation, or that the California delegates were being penalized for coming from a state that hasn't historically been friendly to Republicans.

The second day of the Republican National Convention

CLEVELAND, OH - JULY 19: Delegates from New York and Donald Trump's family including Donald, Jr., Ivanka, Eric, and Tiffany celebrate after the nominating process for the state of New York during the second day of the Republican National Convention on Tuesday, July 19, 2016. (Ricky Carioti/The Washington Post)

[Izadi reported from Washington. This post, originally published July 19, has been updated.]

Correction: This post originally misstated Kaitlyn MacGregor's title. She is communications director, not executive director, of the California GOP.