The father of Missouri's first coronavirus patient disobeyed quarantine and went to a school dance with his other daughter on Saturday evening, officials said.

Villa Duchesne and Oak Hill School will close on Monday after administrators learned of the relationship between the patient and her younger sister — who goes to Villa and attended the social gathering. The father and daughter also went to a pre-dance party which consisted of other students in the St. Louis County area.

“If you attended the dance, please be attentive to any symptoms you are experiencing.” a message by Villa Duchesne said.

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Villa is an all-girls school that serves grades seven through 12, while Oak Hill is a coed school that teaches preschool through grade six.

"We will work with officials to ensure we are doing everything possible to mitigate risk and to maintain our safe environment," said Villa Duchesne and Oak Hill (VDOH) communications director Alice Dickherber, according to the St. Louis Post-Dispatch.

The family was originally told to stay at home after their older daughter – who returned from Italy – contacted public health officials to report having symptoms of the fast-spreading virus on Thursday. She had been self quarantining herself at home with her parents who were not showing symptoms. She went to a hospital on Friday and tested "presumptively positive" on Saturday.

The family was told to stay at home, but the father brushed aside instructions by the state's health department, according to County Executive Sam Page.

They reportedly didn't learn of the diagnosis until after they were at the dance and left immediately, VDOH officials told parents in a letter, according to KMOV.

After going to the dance, Page said officials told the man on Sunday that "he must remain in his home or they will issue a formal quarantine that will require him and the rest of his family to stay in their home by the force of law."

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“The likelihood of any of the Burroughs students contracting the virus is extraordinarily low,” said Burroughs head Andy Abbott in an email on Sunday night, according to the Post-Dispatch.

The first person to test positive in Missouri was a woman in her 20s who had returned from Italy and landed at Chicago O'Hare International Airport on Monday. The woman stayed with a friend in the area before taking an Amtrak to St Louis on Wednesday, according to a spokesman for Page. She had been studying abroad.

"Amtrak is notifying passengers and employees who may have been on the same train, and as a precaution, we have taken the train out of service for comprehensive cleaning and disinfection, and are also working to do a thorough disinfection of the Chicago and St. Louis stations," a statement said.

Investigators are trying to determine who the woman may have had prolonged contact with during her trip back to the U.S.

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“We are looking at her travel schedule, being on trains and planes and staying in hotels, and local contacts.” said state department director, Dr. Randall Williams, according to the paper. “When we say contact, we mean 15 to 30 minutes within 6 feet of the person.”

Over 500 cases and 21 deaths from COVID-19 been reported in the U.S. so far.