STUDIO CITY (CBS) — Whooping cough which was once thought to be almost eradicated is making a comeback.

And there has been a spike in cases across the country. So far, 18,000 cases have been reported in children this year.

“Whooping cough is a respiratory illness. Usually you develop symptoms of a cold for the first week or so and then a severe cough that can last longer than two weeks,” said Dr. Danelle Fisher, who appeared on KCAL9 News on Sunday morning.

“It can be very very dangerous for young children, especially infants less than a year,”

Dr. Fisher is Vice Chair of Pediatrics at Saint John’s Health Center in Santa Monica.

She says in the past couple of years the cases have risen across the country and says improved identification of pertussis and parents who choose not to vaccinate their children are among the potential reasons for the spike.

“Also whooping cough goes in a cyclical fashion so usually every three to five years we have a kinda worse outbreak than at other times,” she added.

The doctor says parents should check with their physician to see if their child has been properly immunized.

“We do recommend a booster for children 11 to 12 years of age but if they missed that booster, they can certainly get it after that. Children who are school-aged typically will have five doses of the whooping cough vaccine before they are six years of age. They are pretty much protected after that until about age 11 or 12,” she said.

Dr. Fisher says whooping cough can be spread through respiratory droplets (coughing or sneezing).

For more information about whooping cough from Saint John’s Health Center, click here.