Canada has a travel advisory for California. A health advisory on pertussis (whooping cough).
In most countries pertussis is a notifiable illness. This year California has had a sevenfold increase in pertussis notifications. All other states have declined a little or remained about the same as last year.
I imagine a lot more people from Canada travel to California to Australia and a sevenfold increase sounds quite a lot. The number of notifications up to 24th August was 3,311. Checking all current health advisories from Canada shows no current health advisory for Australia yet Australia has about 2000 notifications for pertussis each month.
Year to date figures (5th September) show Australian pertussis notifications for this year have reached 14865 (and probably will be lower than last year’s number of 29737). If we look at it another way Australia has so far had 14865 pertussis cases for around 22 million people with California having 3311 cases for 36 or so million people.
This table from the Department of Health (2005 figures the latest I could find a comparison) shows it very clearly.

Most recent notification rates per 100,000 population for frequently notified vaccine preventable diseases, by country of residence
Why haven’t the Canadians issued a travel advisory against Australia. As an Australian I feel ignored!. Perhaps they are worried about 3311 notifications all packed close together in a state only twice as big as Victoria, our second smaller state.
But enough joking.
Pertussis is a life threatening condition. In Australia sixty per cent of all notifications are in the over 20 age group. With a vaccination schedule including vaccination for pertussis at 2, 4, 6 months and 4 years of age (some states have a booster at school) babies under six months of age are at highest risk (21% of notifications in 2008) due to partial immunisation. Between 1993 and 2006 there were 21 deaths in Australia caused by pertussis. 17 of these were in infants less than twelve months of age.