BALTIMORE COUNTY, Md. (WJZ) — A health warning for students at one Baltimore County school after a teacher came down with a possible case of whooping cough–and students may have been exposed.

Meghan McCorkell has details on what parents need to know.

The county health department says the teacher may have whooping cough, a highly contagious respiratory disease, that’s been spreading across the country.

Parents say a fifth-grade teacher at Harford Hills Elementary School fell ill Monday. She was taken to the hospital and diagnosed with a possible case of whooping cough.

“It’s concerning because there’s little kids around and those kids probably have brothers and sisters, so it’s probably going to be real contagious with them, as well,” said David Coogan.

A letter has now been sent home to all parents, warning them to be on the lookout for symptoms.

Whooping cough has spread nationwide with outbreaks reported in Washington, Minnesota, Wisconsin and Colorado.

“Seeing a lot of cases on the rise. Most of the cases started in the West Coast, in California, where a lot of people are not getting vaccinated and have since migrated to the east,” said Sinai Hospital physicians’ assistant Peter Andrews.

In 2011, the CDC reported more than 18,000 cases of whooping cough. That number skyrocketed this year, with more than 34,000 cases already.

Andrews says he saw a surge of cases in Maryland over the summer.

“Whooping cough can definitely be deadly. It is mainly most dangerous in the very young and the very old,” Andrews said.

Vaccination is the main form of prevention.

“I get shots every year still because I don’t want to spread anything to any children,” said student teacher Markie Robinson.

That’s why the school system wants parents on alert.

The CDC reports nearly 300 cases of whooping cough this year in Maryland, up from just 85 last year.

Symptoms of whooping cough include a low fever, runny nose and a cough that gets progressively worse.