''It's difficult to say if it's going up but it's certainly not going down. We have an ongoing issue.''
Dr de Wet said the biggest concern from this involved the risk for babies who had not been immunised.
A number of older children or adults could pick up whooping cough, also known as pertussis, and not necessarily realise they had it, he said.
Because of this, there was a heightened risk that babies or young children not immunised could pick up whooping cough and suffer detrimental health effects.
''For children under the age of 6 months, possibly half of those with whooping cough are likely to end up in hospital,'' Dr de Wet said.
Whooping cough could lead to pneumonia and also could lead to brain damage, convulsions and death. The risk of brain damage ranged from about one in 100 to one in 1000.
The problem began as a runny nose and developed into a dry cough which appeared to come in attacks of coughing. Children often gasped for air, which could lead to a ''whooping'' sound.
''The most important message is to have children immunised,'' he said.
''The whooping cough vaccine is free.''
Dr de Wet advised anyone who experienced a cough lasting longer than two weeks to see their GP.
? For more information: http://www.toiteorapublichealth.govt.nz/whooping_cough
