When Christina Bergin opened the letter informing her that someone in her daughter’s class had tested positive for the coronavirus, she thought: All those efforts and sacrifices taken, all the worrying and being careful about the virus for nearly a year and a half, have gone to waste. And it took only three school days, she said.

Since the pandemic was declared, Bergin said, she has done everything she can to avoid bringing the virus home to her family: She maintains a strict decontamination routine that takes up to 45 minutes every day to get out of her hospital scrubs, cleans her cellphone and protective gear, and takes a shower before daring to hug her husband or two girls after long shifts at University Medical Center in Phoenix, where she specializes in internal medicine.

Furious with the school’s note, she condemned state officials for passing a law in June that prohibits schools from mandating the use of masks or proof of vaccinations, as Arizona and the rest of the United States face a surge in coronavirus infections fueled by the highly transmissible delta variant.

“We have sacrificed so much for you over these past 18 months. And it took only 3 days for you to destroy one of the last things I was hanging onto — the ability to keep my kids safe,” Bergin tweeted.

Bergin criticized Gov. Doug Ducey (R) for “forcing schools to reopen without the ability to implement the same measures that kept kids & staff safe last year,” she wrote.

“And as a direct result, my kiddo, who I’ve managed to keep from coming into contact with a known COVID+ person for 18 long months, was exposed within only 3 days of starting school,” she wrote, adding that her two children still wear masks in school.

“… But if others aren’t masking up also, my not-yet-old-enough-to-be-vaxxed kids can be, will be, & already have been exposed. And that’s on you,” she said, tagging the accounts of Ducey and the Arizona Republican Party.

She said she had opted her children into virtual learning during weeks of highest risk, stopped them from playing sports during the height of the summer and winter surges, canceled birthday parties and had virtual playdates instead of in-person hangouts.

“Why did I do all this?” she said in the Twitter thread. “Because I know how bad this virus can be, what it can do to even healthy individuals.”

She went on to list long-lasting effects of covid-19, the disease caused by the novel coronavirus, that can affect adults and children — including heart damage, scarred lungs, loss of smell and taste, prolonged cough and shortness of breath.

Bergin’s remarks have been widely shared on social media, with more than 25,000 retweets and more than 80,000 likes, a response that “floored” her.

“I thought I was trying to scream out into the void and nobody would ever see it,” she told The Washington Post on Sunday.

But her words echoed the mounting concerns of Arizona residents, school officials, health-care workers and parents who are resisting a state law that bars schools from mask mandates, despite federal public health guidelines that say students and staff members in K-12 schools should cover their faces indoors.

At least six school districts in Phoenix and Tucson have challenged Ducey’s ban on mask mandates, which does not take effect until September. Lawmakers have declared it retroactive to July 1, according to the Associated Press.

The Phoenix Union High School District returned to classes last week, with most students and staff members wearing masks indoors to follow the district’s rules — which counter the state’s ban. The defiance from Phoenix Union prompted the governor’s office to say that the mask requirements are “unenforceable” and that they have "no teeth,” the Wall Street Journal reported.

The governor’s office did not respond to a request for comment from The Post late Sunday.

Last month, the Arizona Medical Association advised schools and education leaders to follow federal health guidelines, particularly the Centers for Disease Control and Prevention’s guidance that says schools should implement mask use, coronavirus testing and contact tracing.

Although Bergin and her husband got vaccinated, her two daughters, ages 10 and 7, are too young for the three vaccines authorized for emergency use for people 12 and older in the United States. During the past school year, Bergin said, she was reassured because her daughters’ school had protective measures in place, including routine use of masks and testing.

In April, Ducey lifted all mask mandates, saying it was time for school leaders to decide whether masks should be required on their campuses.

Arizona Superintendent of Public Instruction Kathy Hoffman (D) criticized the governor’s decision shortly afterward.

“Today’s abrupt removal of the mask mandate in schools is just one example in a long line of decisions that have resulted in Arizona’s embarrassing response to a virus that has claimed over 17,000 lives and impacted thousands more,” Hoffman said in a statement, according to AZFamily News.

“Universal masking — along with other key mitigation strategies — has allowed schools to safely operate during a pandemic,” she added.

Bergin said that with the recent ban on mask and vaccine mandates, there is a lot of confusion about whether schools are allowed to implement other measures such as quarantines after possible exposures.

Her daughter’s public charter school — which The Post is not naming because Bergin says she was concerned for her children’s safety after some users posted offensive comments about her Twitter thread — is not requiring quarantine for students or staff members who may have been exposed to the virus, she said. The school has told parents that their children can attend classes unless they develop symptoms.

In the letter, the school “strongly encouraged” children to wear a face covering for 14 days after the potential exposure.

More than 17,000 children had been hospitalized with covid-19 in 23 states and New York City as of July 29, according to a database of the American Academy of Pediatrics and the Children’s Hospital Association. According to the same data, Arizona has the second-highest number of covid-19-related deaths — 34 — of people 19 and younger.

Banner Health, Arizona’s largest health-care provider, has seen a 95 percent increase in covid-19 cases and a 300 percent increase in ventilator use since July 1. Five percent of those cases were in the pediatrics department, according to a report released Tuesday.

Arizona is one of at least seven states that have barred mask mandates in schools through bills or executive orders, which has prompted a tense debate nationwide about whether officials should allow each school district to decide its own health policies.

Bergin said that she is working with parents, health professionals and experts who are pressuring Ducey and the Arizona Department of Health Services, and that she will send a letter urging them to implement mask requirements and other policies for unvaccinated students.

On Sunday night, Bergin planned to take her daughter’s temperature and give her a rapid coronavirus test to help her decide whether the girl will return to school on Monday.

She said she was “terrified” by the possibility of a positive result.

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