BBC BLOGS - Fergus's Medical Files
« Previous | Main | Next »

How to track swine flu

Fergus Walsh | 17:45 UK time, Thursday, 9 July 2009

Several people have been commenting about an apparent lack of information on H1N1 swine flu. Suggestions have been made that the "real" situation is being covered up.

That has never been the case in my opinion, and this post should provide a wealth of material for those who want it.

I'm grateful to the chief medical officer for England, Sir Liam Donaldson, for allowing me to post up data and images from the technical briefing he has given to journalists.

From now on, there will be a weekly situation report from the Department of Health on the situation in England with separate reports from Wales, Scotland and Northern Ireland.

Which brings me to Sir Liam's presentation.

Tracking data

This pyramid shows what information will be released each week.

Tracking data

First, there is the number of deaths (a total of 14 in the UK so far), then the number of hospitalisations that week, the level of antiviral use and the percentage remaining stocks of Tamiflu and Relenza, and finally the total number of cases from GP consultations and contact with NHS Direct or the National Pandemic Flu Service (when it is up and running).

The swine flu iceberg

This is a good visual way of showing what happens during a flu pandemic. At the top of the iceberg, above the water, you have people with H1N1 who seek help from the NHS, but another group below the water who have the virus but cope okay at home. Then, below the dotted line, the majority of the population who are healthy and unaffected.

The swine flu iceberg

What we don't know is how many of us will fall into each category or when the outbreak will peak. In the last flu pandemic of 1968-70, the UK had a comparatively small outbreak in the first winter, with a much bigger case load the second winter.

Royal College of General Practioners

GPs have a long-standing and well-organised system for monitoring the spread of influenza-type illnesses.

Clearly, they can't and don't swab everyone who comes to them or calls them with symptoms of flu. So instead the RCGP has what's called "spotter" practices who make detailed reports about the sort of symptoms they are seeing. From this, national figures are scaled up.

RCGP figures showing spread of flu-like illnesses

This graph may look daunting, but please persevere. First, let me draw your attention to the two horizontal dotted lines. The lower one is the baseline threshold for flu. This figure is 30 consultations per week per 100,000 people.

The rate is it regarded as significant only when it goes above this. Then there's the epidemic activity line of 200 consultations per 100,000 people.

You can see from the brown dotted line (the big peak) that the last epidemic of flu in England was in the winter of 1999-2000.

Now look at the red line which is 2008-present day. Trace it back to week 52 (the end of December 2008), and you can see that last winter was not a very bad one for flu.

Trace the line forward and you can see the current red line is heading skywards. It equates to 51.9 weekly consultations per 100,000 people for the week ending 5 July. Sir Liam said that this equated - very roughly - to about 27,000 consultations a week.

Of course, not all of those contacting their doctor will have swine flu. The latest estimate is that 28% - or 3 in 10 - will have the virus. The rest will have a bad cold or some other bug.

RCGP consultations by SHA

This graph gives a breakdown of the previous figures by Strategic Health Authority; it shows that the virus has hit some areas of England far more than others.

Strategic health authority figures

The black line shows that flu has reached near-epidemic levels in London, while the red dotted line shows a significant level of activity in the west Midlands. But north-east England is still largely unaffected. As the autumn progresses, we should expect all areas to have significant levels of flu.

Comparing data sources

This is an important graph as it shows a good correlation between the number of confirmed new cases from lab reports (the blue line) and the weekly caseload from the RCGP "spotter" practices.

Graph showing number of confirmed cases from lab reports and weekly case load according to RCGP 'spotter' practices

If these two lines were widely divergent, it would suggest that there was something wrong with the data collection.

Hospitalisations

This is a snapshot of the number of people in hospital with suspected H1N1 swine flu in England as at 8am on 8 July. You can see that children under five and those aged five to 15 represent two large groups, but there are also lots of cases in the 16-64 group.

Number of people in hospital with suspected H1N1

Comparatively few hospitalisations are occurring in the over-65s, who make up the group most affected by seasonal flu. In all, there were 335 people in hospital and 43 in critical care. There have been 14 deaths where swine flu is the cause or the suspected cause.

Apologies to those in Wales, Scotland and Northern Ireland that I can't give you a separate set of data. I would like to have all the material UK-wide, but the Department of Health says there is such an enormous amount of data that it would be impossible. But the Health Protection Agency will give out UK figures on lab-confirmed cases and deaths.

To sum up, this will track the size and spread of H1N1 swine flu in the UK, what the global trends are, whether the virus is mutating or becoming drug-resistant, what level of pressure the NHS is under and the uptake levels for flu vaccine.

The official number of laboratory-confirmed cases in the UK was 9,718 as of yesterday. But this figure is not really worth considering any more, because the vast majority of people are not tested for flu.

Comments

or register to comment.

BBC © 2014 The BBC is not responsible for the content of external sites. Read more.

This page is best viewed in an up-to-date web browser with style sheets (CSS) enabled. While you will be able to view the content of this page in your current browser, you will not be able to get the full visual experience. Please consider upgrading your browser software or enabling style sheets (CSS) if you are able to do so.