On Sunday, when Kathleen Schmidt got a group message that her 12-year-old daughter’s last soccer game of the season was suddenly being canceled, she and her husband both quickly guessed what happened: One of the players had gotten the coronavirus.

That night, her hunch was confirmed: A player on the team her daughter had played one week earlier had tested positive. Alarmed, the 48-year-old book publicist asked a flurry of other questions and learned that the player had attended the game that day despite having a sibling at home who had tested positive.

“It never occurred to me that a parent would send their kid into a game knowing that their other kid was home with covid,” Schmidt, who lives in New Jersey, said.

She says she was told the infected child was tested on Nov. 9 and got the positive results back on Nov. 14 — the day before the last game. A couple of days later, her own daughter started showing symptoms: a cough, severe headache, chills, fatigue and an upset stomach.

Schmidt took to Twitter to use the incident as a key example of community spread. She says you simply can’t trust others to take the same precautions you may be.

“It’s hard to be 100% honest about this because I have to admit I made a mistake. The mistake is that I allowed my daughter to play travel soccer (outdoor) this fall. She had played softball in the summer and there were no incidents,” she wrote.

“The league took all the precautions they needed to and we the parents followed protocol. What I hadn’t thought about was parents from other teams not following protocol. So here we are.”

On Thursday, after the United States surpassed 250,000 deaths from the coronavirus, the Centers for Disease Control and Prevention advised Americans not to travel for next week’s Thanksgiving holiday. They urged people to celebrate in their own homes instead, echoing the pleas of prominent public health officials and medical experts.

As cases surge, activities that may have been less infectious during periods with lower transmission rates can now cause the disease to spread. Whereas local governments previously focused on known superspreader events like weddings, parties and concerts, community spread is occurring via smaller events such as sleepovers, dinner parties and other gatherings between people from different households, especially anything indoors.

Many states are starting to shut down or postpone high school and youth sports. On Thursday, New Jersey pushed back winter high school sports to 2021. Several other states including Utah, Michigan, Illinois and Minnesota are similarly pausing youth sports as part of new restrictions to halt the spread of the virus. In two weeks, Delaware will ban interstate sports.

Doctors say the lack of clear guidelines can confuse the public as we enter the ninth month of restrictions. Pandemic fatigue is playing a role, too.

“One cannot ensure that others are following the same protocols,” Jenifer Lingeman, an emergency physician in Utah said, noting that the biggest risk continues to stem from indoor activities, especially as the weather in much of the country turns colder.

“Public health guidance has been so mixed, fluid and unclear that even if people are trying to do the right thing, they may not be aware of what the right thing is. For example, people tend to overestimate risk from strangers [at the grocery store] and underestimate the risk from family, friends and co-workers,” Lingeman said.

For Schmidt, who recently had pneumonia, the news of the coronavirus case in her daughter’s league was unsettling. As a result of her pneumonia, she now has a heart condition, placing her in a high-risk category.

As someone who canceled two family vacations this year — to Florida and Maine — she says she has tried to be diligent about following protocols. She lives close to her sister, but the two do not enter each others’ homes, she said.

When her daughter started to show symptoms, Schmidt says, she sprung into action, immediately contacting the schools her children attend and their teachers, as well as anywhere she had been in the previous week. Her daughter tested negative for the coronavirus, but she will take her for another test on Friday.

When Schmidt tweeted about her daughter’s potential infection, some people replied that the kids shouldn’t have been playing sports at all.

“It’s easy for people who don’t have kids who are that invested in the sport that they play to say, ‘Well, you should have just not had your kid play,’ or ‘Kids should not be playing sports.’ But for some parents. That’s a very, very heart-wrenching decision,” she said.

She says she assumed all the families would be following the same league-mandated protocols, as well was local and state-level guidance. The experience has been a wake-up call.

It “was a mistake on my part,” she says. “And a hard lesson learned in this case.”

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