NSW Health Weekly Influenza Epidemiology Report – 22nd July

22 07 2009

NSW Health has just released its Weekly Influenza Epidemiology Report, as at 22nd July. This is a fascinating report looking at the surveillance results for influenza in NSW over the past week. The full report is available here. This post will pull a few of the more interesting stats and graphs from it.

Historically high numbers continue to present at Emergency Departments

The first graph that’s worth looking at examines the number of people presenting each week to NSW Emergency Departments with “Influenza-like Illness”. The 52 weeks ended yesterday is the black line. Equivalent periods for the past 5 years are the other coloured lines.

As you can see, the number of people going to Emergency Departments with the flu is substantially higher right now than at any time in the last five years. To quote the report, the number of people presenting with Influenza-like Illness in the past 7 days is “nearly four times higher than the largest seasonal peak of the last 6 years”.

Note that the report also says that this graph is under-reporting the real situation because it fails to capture the people who are going straight to NSW Health’s Flu Clinics – last week that was 1752 people – more than the number presenting to Emergency Departments last week – and only 306 of this 1752 then went on to an Emergency Department:

ed counts 220709

Lower socio-economic areas of Sydney are being hit hardest

The table below shows the total number of admissions to hospital of people with confirmed H1N1 (09) since the start of the pandemic until today. The table is divided by Area Health Service. It also shows the admissions expressed as a rate per 100,000 of population (within the catchment of each Area Health Service).

This table confirms something that the media picked up on a little bit last week: the areas hardest hit by Swine Flu (where “hardest hit” means the highest rate of admissions to hospital) are the poorer areas of Sydney:

Total H1N1 (09) admissions to hospital

Sydney South West is one of the most disadvantaged areas of Sydney. It has a rate of admission to hospital of 19 per 100,000 people, whereas NSW state average is 9 per 100,000, and Northern Sydney and Central Coast (Northern Sydney being one of the highest socio-economic status areas) has a rate of only 5 per 100,000. In other words, the poorest area of Sydney has four times as many people hard hit by Swine Flu than one of the richest parts of Sydney.

Sydney West (16 per 100,000 – almost twice the state average) is another lower socio-economic status area.

Why this marked difference between rich and poor? One reason I’ve heard is that the rates of chronic disease are higher in those areas with lower socio-economic outcomes. As we know, if you already are chronically ill, Swine Flu is likely to hit you harder.

And so, we see the global trends in microcosm: even in a rich Western nation, Swine Flu is disproportionately affecting the poor.

What age groups are getting most affected?

The last graph I want to show is an updated version of one I posted a few days ago.

This graph shows the age distribution of those people admitted to hospital with confirmed H1N1 (09), compared to the average age distribution of those people admitted to hospital over the last five years with “normal” seasonal influenza. In the words of this week’s report:

There is a shift towards young and middle-aged adults in those admitted to hospital with H1N1 influenza 09, compared to those admitted to hospital with normal seasonal influenza over the previous 5 years.

age distribution hospital admissions

It’s nice to see that 45 to 65 year olds are described as “middle aged” by NSW Health!

Note the average or under-representation of people over 65 – this has been a consistent trend with this virus.




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