Three times as many people were infected with whooping cough in 2015 than in 2014, according to NSW Health data.
Data obtained between January and June of both years show an increase from 911 reported cases to 2831.
Only halfway through 2015, the number of reported cases is almost equal to the total number reported for 2014, with outbreaks occurring in Wollongong, the Hills District, the Sutherland Shire, Coffs Harbour and Bellingen.
Whooping cough is an infectious disease usually affecting infants and young children and can be prevented with a vaccine. Much attention has been brought to this issue by the recent death of Perth infant Riley Hughes, who was too young for immunisation, and who died in March.