A St. Louis County woman who had been studying abroad in Italy—Europe's epicenter of the COVID-19 outbreak—was the first to fall ill with the coronavirus in Missouri.

The older sister of a Villa Duchesne Catholic school student arrived in Chicago on March 2 and stayed with a friend for two days before boarding an Amtrak for St. Louis.

The woman had been feeling ill and called the county's health hotline with her symptoms on Thursday after returning home.

According to the St. Louis Post-Dispatch, St. Louis County Executive Sam Page said the infected patient's family was instructed to self quarantine at their home in Ladue after she reported her illness.

On Saturday, state and county officials announced the woman's test result was "presumptive positive" for COVID-19.

But later that night, the father and sister of the infected patient ignored health department instructions to stay home and attended a father-daughter dinner dance with Villa Duchesne and Oak Hill School (VDOH) at the Ritz-Carlton in Clayton.

Page said the County health officials had told the father of the patient:

"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."

You can watch the press conference in the clip below.

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VDOH officials confirmed the father and daughter were not aware of the diagnosis until after they attended the function.

Villa Duchesne – which is an all-girl school from grades seven through 12 – informed attendees of Saturday's dance on social media, writing:

"If you attended the dance, please be attentive to any symptoms you are experiencing."

Page told reporters that the family's opposing response to the situation was "a tale of two reactions" and a "study of how people should and should not react to the coronavirus."

"First, from everything we can gather, the patient had conducted herself responsibly and maturely, and she is to be commended for complying with the health department's instructions."

However, the father's response was not as meritorious.

"The patient's father did not act consistently with the health department's instructions. Instead last night he decided to take his other daughter to a school function."

We learned of this today, and as a result, the county health directors informed him today 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."

Prior to Saturday night's dance, the pair also attended a pre-dance gathering held at a residence of a family whose children attend Villa and the private John Burroughs School.

On Sunday evening, John Burroughs School officials wrote a message to parents informing that the father and the afflicted sister of the Villa student were also present that night.

John Burroughs School head Andy Abbott asked a "handful" of the senior students who attended the pre-dance gathering not to come to school until more information became available.

"Based on the conversations that I have had with medical experts today, the likelihood of any of the Burroughs students contracting the virus is extraordinarily low."

"Still, under an abundance of caution, we have asked them to stay home from school until we have more information."

Amtrak wrote in a statement:

"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."

They said in a news release that the train was taken out of service for an extensive cleaning and reported the train stations in Chicago and St. Louis are also undergoing thorough cleaning.

Investigators with the county health department interviewed the woman for several hours to track down anyone with whom she had close contact with.