A child has become the fourth West Australian this year to be diagnosed with meningococcal disease.
The WA Health Department says the child is recovering in hospital and close contacts have been informed.
Where necessary these people have been given antibiotics to reduce the risk of the organism being passed on to others.
Meningococcal disease is an uncommon, life-threatening illness caused by a bacterial infection of the blood or membranes that line the spinal cord and brain.
It can spread from the nose and throat via coughing and sneezing.
Symptoms include fever, chills, headaches, neck stiffness, nausea and vomiting, drowsiness, confusion, severe muscle and joint pain, and sometimes a rash.
Most people make a full recovery with treatment.
The department said the incidence of meningococcal disease had dropped in WA over the past decade from a peak of 86 cases in 2000 to about 20 to 25 cases a year.
There were 16 cases last year, the lowest number recorded in more than 20 years. More than half the cases were people aged under 19.
A vaccine to protect against the C type of meningococcal disease, which in the past was responsible for about 15 per cent of cases in WA, is free to one-year-old children.