ECDC: Planning Assumptions for the First Wave of Pandemic A(H1N1) 2009 in Europe

30 07 2009

The ECDC have just released a “Public Health Development” entitled “Planning Assumptions for the First Wave of Pandemic A(H1N1) 2009 in Europe”. Read it here (with full references). This paper seems to have been prompted by Norway and the UK re-assessing the assumptions they are using in their pandemic planning. The paper starts this way:

As it is summer in Europe the 2009 pandemic has yet to really accelerate in EU countries but the experience in temperate Southern Hemisphere countries suggests it is inevitable that Europe will be affected by a major first A(H1N1) 2009 pandemic wave in the autumn and winter.  The 2009 pandemic is less severe than might have been expected and ECDC has been made aware by two European Union countries (Norway and the UK) of the updating they have made of their planning assumptions specifically for a first wave of an A(H1N1) 2009 pandemic.

The paper is short, but makes interesting reading and starts to answer a number of questions.

What do we think the “clinical attack rate” might be?

The “clinical attack rate” is the proportion of the population that will catch Swine Flu at some point in the pandemic’s “wave” and display symptoms. The paper says it is assuming a clinical attack rate of 30% (and that another 30% of the population will catch Swine Flu but display no symptoms). By the way, I’m guessing that “displaying symptoms” means getting sick enough to take at least half a day off work – my understanding is that that’s the requirement to be “symptomatic”. Here’s what the paper says about the clinical attack rate it’s assuming:

This is 30 % (The UK clinical attack rate is based on an assumption that half of the infected become symptomatic so this would imply a total infection attack rate of about 60 %). WHO assumptions are that two thirds become symptomatic. Whether the UK or WHO is correct will be determined later when the results from serology become available.   The UK assumptions imply a basic reproductive number Ro in the interval 1.4 – 1.5 which seems to be the case at present in the UK. A Ro of value 1.4 implies a total infection attack rate of about 50 % (which would imply a clinical attack rate of 25 % in the UK planning assumptions). A higher value of Ro of 2.0 implies a total infection attack rate of about 80 % (hence a clinical attack rate of 40% in the UK planning assumptions).

What do we think the “case fatality rate” might be?

This is the proportion of people who catch the virus (and are symptomatic?) who then go on to die. The paper states:

This is one of the most eagerly sought parameters but it is also amongst the hardest to determine with any accuracy. The earliest studies of this pandemic gave a high CFR of about 0.4 % compared to lower rates for the 1957 and 1968 pandemics but higher rates for 1918. The UK estimates are of a CFR of 0.1-0.2 though values of up 0.35% cannot be ruled out as impossible.

Later, the ECDC comments:

Case Fatality Rates (CFR) will also change as more data become available and more stable estimates will take some time to emerge. As some cases will be very mild and not reported the reported figures from official tables of cases and deaths will most often be an over-estimate of the true CFR. Equally though many deaths which result from influenza (seasonal or pandemic) are not attributed to the infection in official causes of deaths and so officially reported influenza deaths are always an underestimate, sometimes grossly so. In previous pandemics it has only been computed with any accuracy once the pandemics were over. It is also important to appreciate that CFR is especially subject to social effects. In poor social settings such as Africa even seasonal influenza can result in CFR’s that are higher than seen in pandemics.

What level of absenteeism might we see?

In the comments section the ECDC discusses the UK’s assumption of a peak in absenteeism at 12%:

The UK predicted peak absenteeism rate of 12 % of the workforce is interesting and fits with the mild illness seen for most people. It suggests that the social disruption effects of the pandemic will be less than feared for other pandemics and that severe social interventions will not be necessary given good business continuity planning.





July 30 – Department of Health and Ageing made a mistake yesterday

30 07 2009

The Department of Health and Ageing figures for today are 20,688 confirmed cases. Yesterday they posted 21,109. Given that these numbers can’t go backwards (like the kangaroo and emu on our coat of arms), I assume the Department meant (not that they’ve said anything) 20,109 yesterday, ie 1,000 fewer cases. That still means that the increase yesterday was 1,083. And the increase to today’s number is 579. Nonetheless, this readjustment brings the 7 day moving average (of new daily confirmed cases) down from the 900s to 712.

There seems to be no mistake with yesterday’s hospitalisation figures. Figures today have moved around a bit – total number of people in hospital slightly down, total number in ICU up.

The graphs below tell the story. As always, you can see these graphs in more detail, as well as some others, at the top of this blog (at “Australian Swine Flu Graphs“, which I try to update daily). You can also, by the way, double-click on any of these graphs and that should blow them up for you to get a better look.

7 day move avg australiaaust hospitalisations





NSW Health weekly epidemiology report – 29th July

29 07 2009

NSW Health has just released its Weekly Influenza Epidemiology Report, as at 29th 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. As we did last week, we’ll pull some interesting graphs from it.

Historically high numbers continue to present at Emergency Departments

Firstly, let’s look at 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, despite the fall in the last week, the number of people presenting to Emergency Departments is still much higher than for the same period in any of the last 5 years.

ed counts 220709

What age groups are getting most affected?

And now, let’s look at how different age groups are being affected by this virus compared to a “normal” seasonal influenza. 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





Wednesday update: 2,000 new cases for the second day running

29 07 2009

UPDATE AS AT JULY 30: It seems the Department of Health and Ageing made a mistake with the total cumulative figure in this update of 29th July. They wrote 21,109 total cases. It’s pretty clear now (as at July 30) that they meant 20,109. See my July 30 post.I’ve left my original July 29 post, with the Department’s mistake, standing here:

So, now it’s a bit more concerning. The Department of Health and Ageing have reported another 2,000 new cases today (2,083 to be precise). This takes the 7 day moving average of new daily cases to 915. That’s right – we have averaged 915 confirmed new cases of Swine Flu every day for the last 7 days.

So, what’s behind this? I guess it’s that we are approaching the peak (flu usually peaks here in August). But, as one of the commenters last night implied, it’s as much about how much testing you choose to do as anything else. There are better ways of seeing the spread of the pandemic (eg hospitalisations etc). Nonetheless, I think this new daily cases figure is not a bad proxy for the current spread of the virus: in as much as, I expect the 7 day moving average will trend down as we come off the peak (hopefully in a few weeks). So, it remains worth watching.

The graphs below tell the story. As always, you can see these graphs in more detail, as well as some others, at the top of this blog (at “Australian Swine Flu Graphs“, which I try to update daily).

7 day move avg australiaaust hospitalisations





Tuesday in Australia: almost 2,000 new cases

28 07 2009

So, the Department of Health and Ageing caught up with their weekend backlog and published 1,965 new cases in their daily H1N1v update. If it were a real 24 hours worth it would be alarming, but it’s clearly to make up for the under-reporting of the last few days (see yesterday’s post).

With this update the 7 day moving average has snapped back to its steadily increasing trend. It’s now 713 – the largest number yet. Hospitalisations remain steady – at their recent record highs.

7 day move avg australia

aust hospitalisations

You can see these graphs in more detail, as well as some others, at the top of this blog (at “Australian Swine Flu Graphs“, which I try to update daily).





27th July update: fall in new cases reported

27 07 2009

We’ve had a marked fall in the number of new cases reported here over the last 72 hours. The new cases reported by the Department of Health and Ageing for the last three days have been: 201, 0, 293. I suspect this is just reporting hiccups around the weekend – but we haven’t quite had this pattern before. So let’s see. Far too early to call the peak. Our worst flu month is traditionally August. As a result of the low reported numbers, we’ve seen the 7 day moving average fall quite sharply:

7 day move avg australiaThe number of people in hospital with Swine Flu has, unfortunately, not fallen. The numbers are still at their highest levels ever since the start of the pandemic:

aust hospitalisations

You can find large versions of these graphs in the normal place: in the Australian graphs at the top of this blog.





No update for today from Department of Health and Ageing

26 07 2009

No update today from the Department of Health and Ageing. They’re probably having Sunday roasts with their families… I’ll post the next lot of Aussie stats tomorrow, although probably later than usual.