ACT Health said the young woman's condition had improved and she was in a stable condition at Canberra Hospital.

The cadet was taken to Canberra Hospital after she went to the Duntroon Health Centre on Saturday evening with a fever and a "flu-like illness over about 24 hours".

Acting ACT chief health officer Andrew Pengilley said meningococcal disease was rare and not particularly infectious.

There had been just 40 cases in the ACT in the past decade and authorities did not expect the cadet's illness would lead to other cases of the disease.

Meningococcal disease is a potentially deadly disease and although rare, it is most common in children under the age of five and those aged 15-25.

Symptoms include fever, neck stiffness, severe headaches, sensitivity to bright lights, vomiting, joint or muscle pain, rash or coma.

Dr Pengilley said although meningococcal disease was rare, anyone feeling unwell with symptoms such as high fever, headache or rash should see their doctor.

Visit health.act.gov.au/publications/fact-sheets/meningococcal.