(WHAS11) -- There has been a dramatic spike in the number of cases of whooping cough.
There have already been 18,000 cases this year. more than double what we saw at this time last year. Nine people have died so far.
It could be the most severe outbreak since the 1950's.
Whooping cough attacks all ages, but it is most dangerous to children.
The classic symptoms are runny nose, fever, and severe coughing. The CDC is trying to determine the cause of the spike.
Doctors suspect an evolution in the bacteria that causes the illness or shortcomings in the vaccine.
Children should get vaccinated starting at two-months-old. Adults are being urged to get vaccinated as well.