A teenager is one of two West Australians diagnosed with potentially deadly meningococcal disease in the past week.
The WA Health Department said today the pair were being treated in hospital, with the teenager improving but in a serious condition while the middle-aged adult was stable.
There was no link between the cases, the department said.
People who may have come into close contact with either patient have been given antibiotics to reduce the chance of infection.
Meningococcal disease is a life-threatening illness due to a bacterial infection of the blood or membranes that line the spinal cord and brain.
There were 19 cases notified in 2012, the lowest number in more than 20 years.
A vaccine to protect against the C type of meningococcal disease, which in the past was responsible for around 15 per cent of cases in WA, is provided free to children aged 12 months.