As Australia moves into regular flu season, the annual period of people coughing on trains, sucking Butter Menthols and calling in sick, the national swine flu infection tally is moving ever closer to 2000. This is after all the world’s first flu pandemic in 40 years.

But what about regular human flu? The sort that comes every winter? Could swine flu frenzy be covering for a rise in the spread and severity of the influenza responsible for thousands of sick days — and deaths — every year?

Crikey spoke to flu experts to get the low-down on human versus pig: the battle of the flus.

Associate Professor Heath Kelly, head of epidemiology at Victorian Infectious Diseases Reference Laboratory:

There’s been a lot more testing this year than you’d expect usually, and that’s due to the anxiety caused by swine flu — I’ll call it that to make it easier.

There is normal human flu co-circulating with swine flu. Our surveillance shows the flu numbers are going up very rapidly. The biggest rise is in our home service, and they think it’s more to do with people being anxious than it is people being really sick.

We don’t think human flu is more virulent this year.

Spokesperson for Dr Rosemary Lester, Victoria’s acting chief medical officer:

There is seasonal flu around, we know that. In the ‘contain’ phase, we did extensive testing for H1N1 specifically, and through that process we have found seasonal flu as well. Up until the 4th of June — the most recent accurate tests we have — we had 1244 laboratory-confirmed notifications of influenza. Of those 1244, 752 were H1N1. That leaves 492 other flus — the seasonal flus that you’d expect.

Those figures tell us two things. Firstly, when you go testing at the levels we were testing, you will find the flu. Secondly, in a normal flu season we wouldn’t have 492 flus identified, because we wouldn’t do the same testing.

The shift for us on the 4th of June to the phase of “modified sustain” means we aren’t doing broad testing. But there will be tests for those at risk, through our sentinel surveillance team. We have 80 GPs around Victoria — metro and rural — and they will continue to report influenza-like illness in their patients. They will continue to do — based on their clinical judgment — specific testing. And, from that data, we will be able to get an accurate picture, and to compare it to last year.

I don’t think human flu is more severe this year, in terms of what we’re seeing in terms of hospitalisation, and we have good data on that. Although, the things to say with H1N1 is: it is mild in most cases, although it can be severe, which is why we’ve seen four people hospitalised. We haven’t seen anything that tells us there’s anything different about regular flu.

Clinical Prof Dominic Dwyer, Centre for Infectious Diseases & Microbiology, Westmead Hospital, Sydney:

There certainly has been a rise in the number of flu cases. It varies from state to state. In NSW, in the last few days, we’ve seen an increase in the number of human seasonal influenza.

There’s human seasonal influenza, those outbreaks occur over about an eight-week period over winter — and that’s what accounts for the rise in hospital admissions and absenteeism and so on — and that’s what we’re seeing that’s starting now.

The number of people presenting to emergency departments with flu-like symptoms is increasing, reflecting the increase we’ve seen in the laboratory. And if more people are presenting to emergency, you can bet your bottom dollar more people are presenting to their GPs.

As to how severe it is — it’s too early to tell, because it’s literally the first week. It’s like a pyramid — you’ve got the people at the bottom who are infected, and the people at the top who might die, and then you’ve got everyone in between.

Prof John Mathews, School of Population Health, University of Melbourne:

The best way to talk about it is this: the flu we get every year, call that seasonal flu. And then the pandemic flu contains genes from pigs and birds, so it’s an assortment. Calling it swine flu helps, because it’s different, but it probably worries people unnecessarily. It is human flu now, because we’ve seen it in humans.

Because of concerns about pandemic flu, people have been more alert to the flu, and people have been diagnosed more. In a normal flu season, we probably wouldn’t see as many cases this early in the season. But it isn’t alarming — as you know, there have been no deaths in Australia.

At the moment, this virus is behaving much like seasonal flu. It seems to spread more easily because immunity to seasonal flu is not so good for this mutated version, therefore more people are susceptible.

In a normal flu season, around five per cent of the population get infected, although it can be up to 20 per cent, probably because others have immunity from the year before. But when a new virus appears, the immunity isn’t specific enough to protect people as well. This is particularly the case with children, because they’ve only been around for a few years.

Seasonal flu this year seems to spread more easily, but there’s nothing to convince us that in Australia it’s more severe than seasonal flu in any other year.