CHICAGO (WLS) — A case of tuberculosis occurred at the freshman/sophomore campus at Waukegan High School, officials said.

The Lake County Health Department said a person was recently diagnosed with active tuberculosis, also known as TB. Officials have not said whether the case involves a student or staff member.

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School is in session at Waukegan High School this week after a thorough cleaning over the last couple of days. It was late last week when they discovered a case of active tuberculosis in the school community. Since that time, officials said they are taking every precaution to prevent it from spreading.

“Our focus is on preventing spread ongoing in our community in that school,” said Lake County Health Department Executive Director Chris Hoff.

Tuberculosis is considered a very serious illness. It is caused by a type of bacteria called Mycobacterium tuberculosis, according to the Centers for Disease Control and Prevention.

It is one of the deadliest infectious diseases in the world, though it rarely occurs in the United States. It spreads through the air by coughing, sneezing or even laughing.

The person diagnosed with tuberculosis has been isolated. The principal sent a note to parents Friday, explaining the situation and what they are doing about it.

Students and staff identified as close contacts have already been notified separately via email with any recommended actions. To respect their privacy, ABC7 will not be sharing any additional details.

As a precaution, the school is undergoing recommended cleaning procedures.

“We are taking it seriously, working with the school to make sure people have information, hoping parents will get their kids tested,” Hoff said.

So far, the school is aware of just one person diagnosed with the illness. It is considered rare.

Last year, there were just 353 cases statewide, 18 of them in Lake County. In Chicago, there were 164 cases. It all amounts to fewer than three cases for every 100,000 people.

Some people become infected with tuberculosis germs that live in the body for years without causing illness. This is known as inactive TB or latent TB.

Tuberculosis is treatable, but the sooner it is diagnosed, either in active or latent form, the better, especially in a school.

Signs and symptoms include a cough that lasts for three weeks or longer, coughing up blood or phlegm, chest pain, weakness, fatigue, weight loss, loss of appetite, fever, chills and night sweats, according to the CDC.

“School or work, places where people spend a lot of time in close quarters. Those are the environments we’re worried about. So, that’s why we’re reaching out to the students and families,” Hoff said.

School and health department officials are cohosting an information session on Tuesday night. It will be virtual, for students, staff and parents to get more information about tuberculosis.

ABC News contributed to this report.