CHICAGO (CBS) — An woman who flew into O’Hare International Airport from Italy and then took Amtrak from Chicago to St. Louis last week has tested positive for the coronavirus, officials have confirmed.

On its website, Amtrak said it had received a notification from St. Louis County, Missouri that a customer who has now tested positive for coronavirus traveled on Train 303 on Wednesday, March 4, using stations in both Chicago and St. Louis.

CBS affiliate KMOV-TV in St. Louis said the woman is 20 years old and tested positive for coronavirus on Saturday. She was the first coronavirus case in Missouri.

Missouri Gov. Mike Parson said the woman had been studying abroad in Italy and flew through O’Hare International Airport before pickup up Amtrak to St. Louis, KMOV reported.

It was not immediately learned how the woman got between O’Hare and Union Station, where Amtrak operates from Chicago.

The customer did not have symptoms when she boarded the train, Amtrak said.

Amtrak said it is working with public health and emergency management teams to investigate the situation. The agency has reached out to the crew that operated the train and all the customers onboard, as well as Chicago and St. Louis station personnel.

On Sunday evening, cleaning and precautionary measures were under way at Union Station. As CBS 2’s Jeremy Ross reported, crews were cleaning the benches at the train depot as the busy travel hub underwent additional sanitation.

Hand sanitation stations can also be found throughout Amtrak’s hallways.

It is unclear how many passengers could have come into contact with the woman.

The train itself has been taken out of service for disinfecting, as have the stations in Chicago and St. Louis, where Amtrak operates from the Gateway Transportation Center.

Meanwhile, the woman was being treated at Mercy Hospital St. Louis for a fever and breathing issues by Friday, and a coronavirus test came back presumptive positive on Saturday, KMOV reported.

Parson said as of Sunday, the woman had been released, as the local health department decided she was not sick enough to stay at the hospital, KMOV reported. She was kept apart from other patients at the hospital, KMOV reported.

“The young woman and her parents are currently quarantined in her parents’ home in St. Louis County,” St. Louis County Executive Sam Page said Saturday.

CBS 2 has reached out to O’Hare International Airport about the St. Louis County case, but had not heard back Sunday night.

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Illinois has had seven confirmed cases of coronavirus as of Sunday, of which this Amtrak case is not one.

Also Sunday afternoon, Chicago and Illinois health officials announced that a Chicago man in his 60s was the seventh confirmed coronavirus case for the state. He was hospitalized in serious condition Sunday afternoon.

An investigation by the Chicago and Illinois departments of public health were ongoing Sunday afternoon. But based on what is known, the case has not been linked to any travel or any already-confirmed event.

On Friday, city and state officials announced the sixth Illinois patient was a special education classroom assistant at Vaughn Occupational High School.

Vaughn will remain closed through March 18 after the woman, in her 50s, tested positive Friday.