A young adult is in a stable condition in a New England hospital with confirmed meningococcal disease.
Close contacts of the patient have been prescribed clearance antibiotics to prevent further transmission of the disease.
Public Health Physician Dr David Durrheim stressed that while meningococcal disease is a life-threatening illness, in most cases early detection and treatment resulted in a complete recovery.
"Meningococcal disease can be potentially deadly and if anyone suspects symptoms, they should seek medical attention immediately," Dr Durrheim said.
Meningococcal C vaccination is free and recommended as part of routine childhood immunisation at 12 months of age.
NSW Health is also offering meningococcal vaccine that covers four strains (A, C, W and Y) to all students in Years 11 and 12 this year.
Students who miss school clinics, or young people aged 16-18 years who are not attending school, can see their GP for free meningococcal ACWY vaccine.
The first signs of meningococcal disease may include pain in the legs, cold hands and feet and abnormal skin colour.
Later symptoms may include high fever, headache, neck stiffness, dislike of bright lights, nausea and vomiting, a rash of reddish-purple spots or bruises, and drowsiness.
Babies with the infection can be irritable, not feed properly and have an abnormal cry.
Meningococcal infection does not spread easily. It is spread by secretions from the nose and throat of a person who is carrying it and close and prolonged contact is needed to pass it on.