CHICAGO (CBS) — A third student at Oak Park River Forest High School has been diagnosed with whooping cough, school officials said.

Known as pertussis, whooping cough is a highly infectious illness that is easily transmitted through coughing and sneezing and may last for several months.

Workers are “diligently performing extra sweeps to clean and sanitize the building,” OPRF said in a statement.

A fourth case involving an adult was also reported.

Anyone can get pertussis, but it can be very dangerous for infants and people with weakened immune systems.

Children with a cough should stay home from school and activities and see a doctor.  A person with pertussis should stay home for five days and be treated with antibiotics.

Protection against pertussis from the childhood vaccine, DTaP, decreases over time.

Older children and adults, including pregnant women, should get a pertussis booster shot called Tdap to protect themselves and infants around them.