Australia has a strict policy when it comes to embarkation, and monitoring all incoming foreign nationals for signs of sickness or infection. So, if you are applying for a visa to visit Australia, then you need to know that the government of Australia is empowered to subject you to health examinations and even temporarily hold you in a secure and sterile environment while they evaluate your health. This is why it would be a good idea to subject yourself to a complete medical test, prior to applying for an electronic travel authority visa.
What happens, if you get sick onboard?
If your application to visit down under has been approved by the electronic travel authority then you would have to make sure that you take better care of yourself so that you do not get sick, prior to your departure. It is essential that you visit your doctor often, and get yourself checked out even if you get a sneeze. But if you happen to fall seriously ill during the flight itself, then the authorities would be notified of the same immediately and you would be placed in a temporary quarantine, until your health condition is evaluated. The electronic travel authority empowers you to travel to down under, but not to carry infectious diseases along, for the ride. So the government of Australia has initiated strict health measures, as a way to protect its citizens from any health outbreaks, pandemics, etc.
How long would you be quarantined?
You would first be held in a secure and sterile environment, usually at the airport while an initial on spot diagnosis is carried out. After which, you would be shifted to a local hospital with a secure and sterile environment where further tests would be carried out. And once the diagnosis is confirmed you would be treated for the condition and if you can recover your health, then you should be able to continue with the rest of the trip, as initially planned.