Increase in pertussis cases – Pertussis is a highly contagious respiratory infection that is increasing in incidence. Infants aged less than six months are most susceptible to the severe complications of pertussis. Adults are the main reservoir of infection due to waning immunity after vaccination in childhood. Pertussis in adults is predominantly atypical, without the characteristic “whoop” and often presents as just a prolonged cough, which may go undiagnosed. This means that transmission to babies and other persons can occur readily

More information:
http://health.vic.gov.au/chiefhealthofficer/advisories/advisory-2015-01-increase-in-pertussis-cases.htm