When Nicola Roxon, the Federal Minister for Health gives rolling press conferences about flu, there is one thing we can be sure of: the new outbreak of swine flu is no ordinary flu.
By Tuesday morning the World Health Organisation had raised its pandemic alert level up to four out of a possible six as new cases emerged in Europe, America and Australia.
We need to be careful not to panic.
So far, this outbreak of swine flu has crossed the species barrier and it has spread quickly from human to human. It appears to have mixtures of human, bird and various swine subsets in its make-up. Most people who have caught it have only had mild cases of flu.
However, of the more than 1600 Mexicans who have caught it, more than 150 have died. What is alarming public health experts is that among those who have died are apparently healthy adults.
The difference between the Mexican and all other cases is a variable that has not yet been properly explained.
But it may be that the Mexicans were not as fit as others confirmed with the disease. It's a common pattern during a disease crisis; people in the majority world tend to be more vulnerable to more serious levels of illness and so die in higher numbers.
We fear the pandemic because of the Spanish flu of 1919. In that pandemic between 20 to 40 million people died worldwide, more than the number killed in the First World War. It was one of several times last century when swine flu crossed the species barrier, but it was the most serious.
Since then public health officials have been expecting another outbreak on the same scale. The more time passes without one, the more they worry that it is getting closer. Every time swine flu crosses the species barrier and turns up in humans, they become extremely nervous.
The consequences of an outbreak of swine flu in America, at Fort Dix, New Jersey, in 1976, are still discussed in medical journals. Out of fear of another horrendous pandemic, American health officials reacted quickly. Before long, a massive flu vaccine program was begun, with the goal of avoiding the scale of the 1919 losses.
The program was not abandoned until 25 per cent of the population had been vaccinated. Epidemiologists and others still discuss the futility of the exercise, observing that a