James Cook University researchers have gathered historical data from reports of irukandji stings occurring in the Cairns region during the past 60 years and concluded the season has grown from two months every year in the 1950s to a current season that lasts six months.I'm sorry, what was that you just said? The last sixty years? They didn't even find a jellyfish responsible until the early 1960s, so exactly how are you assessing historical reports from the 1950s?
A north Queensland doctor named Jack Barnes was the first to discover the causative organism and then describe it in the landmark, and rather bizarre, 1964 MJA article "Cause and Effect of Irukandji Stingings". The intrepid doc spent countless hours looking for a likely offender, and then when he thought he might have a suspect, eschewed testing it on animal models in favour of testing it on himself. When that subsequently hurt a bit, he tested it on a male lifeguard and his own 9 year old son. They all wound up in hospital and in honour of his efforts, the jellyfish he had found was named Carukia barnesi in his honour. (Which to my mind stands as a fine example of the Australian penchant for taking the piss.)
Prior to this stellar proof that "they don't make science like they used to", there was such a thing as Irukandji Syndrome that had been recognised in divers and waders in northern Australian waters. However, extrapolating from suspected case reports is problematic even to this day, as there is often diagnostic confusion between decompression sickness (the bends) and myocardial infarcts (good ol' fashion heart attack). The first reported case of a diver even remembering SEEING a jellyfish around the time they got sick was in 1997, and often the onset of the symptoms follows sometime after when exposure is thought to have occurred.
Couple all this with the fact that we know almost nothing about the jellyfish ecology, or even how many species worldwide are capable of producing an Irukandji syndrome. Oh, and the fact that reef water temperatures aren't as far removed from the average as hysterics would have you believe, AND the fact that the human population of the state has increased almost threefold since 1961.
I'm thinking they shouldn't be so quick to extrapolate the population size of a species with a virtually unknown ecology from the number of presumed case presentations. I would say its far more likely that any trend you're looking at relates more to 1) the growing popularity of scuba diving and snorkelling as a recreational past-time and 2) cheap air travel resulting in swimming in stinger season contrary to all common sense because you're "on holiday".
I would also question how they even accessed historical medical records? Theres alot of Australian hospitals that are only making the move to digital records in the last year or so, and old hospital paper records don't get kept that long. The last time I had to find some personal records, and this is just from the eighties, they literally sent some bloke out to check the garden shed and then got back on the line to report that unfortunately they had been "archived" (with extreme prejudice), i.e. in a furnace.
Even in 2006 doctors were writing to the Editor of QJM to say:
We know little about the lifecycle of these jellyfish, and currently there is no antivenom. We hope that the recognition that Irukandji syndrome is due to many jellyfish worldwide, will spur further research into identifying the ecology of the jellyfish and the venom components responsible, and hopefully produce an effective treatment.
Its kind of amazing that one of the "researchers" involved in this study is a PhD candidate. Sigh. They really don't make science like they used to.