The Health Department is warning people who develop measles-like symptoms to get a check up, after a spate of cases in the past two weeks.
Eleven people have come down with the infection since the end of July, six of those in the last week.
It's believed the most recent cases became infected when they made contact with two people who brought their infections home from overseas.
The previous five cases were infected while travelling overseas in Bali and the Philippines.
As these cases visited numerous public places in Perth while they were infectious, a number of other people have potentially been exposed to the highly contagious illness.
Director Communicable Disease Control, Dr Paul Armstrong said public health staff had been providing information to people who were potentially exposed to the most recent cases where they were known, but it was not possible to identify and specifically warn people who were in public places.
“Every measles case is treated as a public health emergency because of the risk of local spread – including to those most vulnerable to infection such as infants too young to be vaccinated, pregnant women and those with compromised immune systems," said Dr Armstrong.
Early symptoms include fever, cough, runny nose and sore eyes, followed by a red blotchy rash about three days later. The rash usually starts on the face and spreads to the rest of the body.
Anyone who thinks they might have measles should call ahead so that they can be isolated immediately on arrival at the GP surgery or Emergency Department, to prevent infecting other patients and staff.
People who are concerned they may have measles and require medical advice after hours can contact Healthdirect on 1800 022 222.