Tuesday, April 28, 2009

So what's the mortality rate for this swine flu ? Why the mortality in the US compared to Mexico just seems low, but isn't

The current outbreak of swine flu is clearly very contagious. It is also clearly very wide spread in Mexico, given the location foreign travellers are coming how with infections from. The two cases in the UK (Scotland) have already created a significant number of other cases of concern.

You hear case numbers mentioned on the radio, but they are very imprecise. Today's radio 4 Today mentioned 2000 cases - but is that current or in total. If its in total then 150 deaths for 2000 cases is a very alarming mortality rate. I assume there are vastly more cases which people have recovered from than are being reported. (Update Reuters have a report of world case number here - if they contain all known cases rather than current cases then mortality would seem to be indicated as high. The Mexican figures suggest 9% - all the figures I've used here are 0.5% - lets pray that in reality the number of mild and unreported cases in Mexico is far higher as we already know its very infectious.)

However if the flue kills about 0.5% of cases ( at the lower end of the 0.5-2% range UK planning seems to think likely ) then there are 30,000 cases in Mexico.

Mexico city has a population of 20,000,000 and the country 109,000,000. That would mean a final casualty rate of 272,500 - ie quarter of a million, assuming 50% of the population get infected.

The UK equivalent is 150,000 fatalities. If mortality is higher or transmission is more effective then that number goes up a lott ( the govt sees 755,000 as its top end projection ). The weak response from the UK government so far, which has consisted mostly of arrogance about being the best prepared country for the coming storm ( now where have we heard that before ? ) does not fill me with confidence.

Given the high amount of medical attention those lucky enough to be the early victims will receive it reasonable to assume mortality can be kept much lower than that initially.

None of this means the virus, which is now in the UK and US is any less deadly than Mexico.

I assume our media's science correspondents are keeping this quiet. But that's a mistake. To avoid panic people need to be assured that their government is levelling with them.

If we are to accept the decisions of doctors and civil servants about who gets treatment or a ventilator and who dies at the peak of an epidemic we need to have trust and faith that they are being open and honest. The alternative is a break down in public order just at the time that the police and military can't cope.

If the mortality rate is 0.5% then given the 40-60 cases identified outside the US we can't really tell anything about the mortality rate, except to rule out ebola type mortality. So far for the chances of a fatality to reach 50%, without medical intervention, would require 138 cases.

This is why the reports of the disease being milder else where are not reassuring.


Take a look as some pandemic flu (avian) simulations for the US and the expected profile for the UK. What you'll see is a sort of phoney war at the start, until centres of infection spread then the explosion of cases.

Also a typical curve of the profile of an epidemic from the UK govt report "Pandemic Flu" by the Cabinet office.

Update: Sad news for first US death of a child here. That's one fatality in 68 cases. Not enough yet to be statistically sure of large scale outcomes ( this would roughtly indicate a mortality of about 1.4% despite what is presumably very good health care in the US,. If sustained it would be very bad news. The other key issue is transmission rates [unknown currently] ). Cause for concern and a tragedy for their family.

PS My view has now changed from an earlier post. I think this is alarming. Most alarming of all is the thought that the same govt that couldn't control foot and mouth is now going to be responsible for trying to save my family and community.


ConstantlyFurious said...

You've got me worried now (as well as furious).

As I say here, its all quite entertaining when the Government fucks up a trip to Obama's house, or their expenses claims, or their smear campaigns.

It'll be a lot less hilarious when they fuck this up..

neil craig said...

I initially assumed the Brits being tested would turn out not to have it. Since there are officially 1,600 cases in Mexico the odd of any person a tourist meets would be about 1 in 60,000. My fuess is it is much more common than reported & this explains the high death rate in Mexico.

Man in a Shed said...

Neil - there are two interpretations of the Tourists getting infected.

1) Lots more cases in Mexico than reported ( which is good because it means the disease is less deadly than we might fear ).
2) Transmission is very effective and fast. Fewer people infect more people quickly. We have a little girl who is a confirmed case who was on the same flight as other people who where earlier diagnosed. That sort of transmission is scary.

The UK govt is still implying to people that they are only infectious once symptoms show, yet advice from the US CDC is that you shed the virus a day before symptoms. So if 2 is true the UK will fail very quickly to contain our cases.

neil craig said...

But (2) would also mean lots more Mexicans than admitted being infected so either way it isn't that bad.

Downside is that flu is much more infectious & damaging during the winter because it weakens already weakened systems. So like the 1918 epidemic we may see it worse this winter. And if we are headed for blackouts because we have been playing around with windmills ....