Tuesday, October 27, 2009

H1N1: Australia Edition

Somewhere in a news report I was reading recently, the fact that Australia had reported an increase in the confirmed flu cases over 8 times the normal seasonal flu was highlighted as a reason for the near-hysterical response by some governments and people.

That was an impressive number I thought, and quite convincing when held in isolation, but then I remembered that the Australian flu season is over now, and they did not have the benefit of a vaccine either. So it got me to thinking, that Australia is a similar nation to Canada in terms of infrastructure (health care, etc..) and population (large nation with areas of dense population density and areas of sparse population density). It might serve as a useful analogy to see how dangerous H1N1 really is.

Figure 1: Confirmed Flu Cases in Australia by Week [1]

As shown in Figure 1, there really has been an increase in the number of confirmed flu cases in Australia, 8.4 times the 5 year average in fact according to the Australian government. But these are only 'confirmed' cases this year, and in years past there's no guarantee that people didn't experience flu like symptoms only to decide not to report them or confirm them with a laboratory. In effect, because the testing rates this year are not similar to testing rates in the past its a useless measure.

A more useful measure perhaps is how often general practitioners have patients who are experiencing 'influenza like illnesses' (ILI). Australian government records helpfully record that the rate of observed ILI cases in 2009 is actually lower than in 2007 and similar in magnitude (although not in time) to 2008.

Figure 2: Rate of ILI in Australia by General Practitioners [1]

Alright, one might argue, but what if people are so sick they're not going to their family doctor and are instead heading straight to the emergency room, this wouldn't be reflected in the rate in Figure 2. This is true, however, records show that the number of presentations at emergency rooms in Australia with ILI is similar to 2007 but significantly higher than 2008. The 2007 rate was attributed to what the report says is a public response to a few cases of child deaths associated with influenza. Interestingly enough, there might be something to this, the number of hospitalizations in Australia from influenza is typically around 2000/year, whereas this year it is around 4000.

What can we take away from this? Well, the rate of confirmed influenza has increased by 8 times, but the number of hospitalizations has only doubled. So we can either confirm the hypothesis that they are indeed testing more often or confirm that influenza is less dangerous percentage wise because the rate of ILI hospitalizations over the number of lab confirmed influenza has actually decreased. Moreover, its also possible that with all the talk about H1N1 going around, that doctors are taking fewer chances and are hospitalizing patients more often than normal. After all, their fundamental rule is to do no harm.

Figure 3: Rate of ILI Presentations at Emergency Rooms in Australia [1]

Finally, just in case you weren't convinced by all that, it would be expected that if influenza was as widespread and as dangerous as some are making it out to be, that there would be a significant increase in the absenteeism reported. As seen in Figure 4, this is absolutely not the case.

Figure 4: Absenteeism reported in Australia [1]

The message I took away from all this information was simple. Get your flu shot if you want, but lets not panic, and lets not get carried away worrying about H1N1.

[1] Australia Influenza Surveillance Summary Report, Australian Government [link]

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