How are H1N1 flu projections calculated? | Healthland

A new headline-grabbing report from the White House claims that swine flu could plausibly infect up to 50% of Americans, causing flu symptoms among some 60 to 120 million of them, and leading to as many as 1.8 million hospitalizations and 30,000 -90,000 deaths.

Where, exactly, do numbers like these come from? The new report was put together by the President’s Council of Advisors on Science and Technology. It turns out the predictions are based on just a couple key facts:

The virus seems to be transmitted from person to person at the same rate as in previous flu pandemics — a rate that’s much higher than that of the regular seasonal flu. Rapid transmission suggests that the total number of infections could be very high.

The death rate for people who catch H1N1 seems about the same as that for seasonal flu. The White House advisors estimate that, so far, between 1 in 1,000 and 3 in 1,000 people who have needed medical help then end up dying. Assuming that this normal death rate continues during flu season, the total number of deaths is projected to be much higher than normal because of the higher number of infections.

And that’s basically it. The Council’s report notes prominently and often that, even though the up-to-50%-infected scenario is plausible, it is by no means certain. That’s because both of the basic facts above — the infection rate and the case fatality rate — are still a little fuzzy. They’re hard to measure in the first place, and it’s not totally clear whether they’ll change as the pandemic progresses.

So why all the fuss if the estimates are still murky? As Homeland Security head Janet Napolitano put it yesterday in a statement: “It is not possible to predict how the 2009-H1N1 influenza virus or the upcoming influenza season will play out, but it is best that we plan and prepare for a resurgence of H1N1 flu.” Things may not develop the way the White House advisors suggest, in other words, but given available evidence it’s still a fine idea to brace ourselves.

There’s one other very good reason that this year’s flu pandemic has experts unnerved. Seasonal flu typically kills only the elderly, with 90% of victims 65 and older, according to the new White House report. (That’s one of the reasons we don’t consider seasonal flu a very serious disease, even though it kills thousands of Americans very year; the public just doesn’t get too upset over a 92-year-old passing quietly in the night.) But the pandemic flu has hit young people and working-age adults unusually hard, just as the deadly 1918 flu did. So far 83% of U.S. deaths and 71% of hospitalizations have occurred among people aged 5 to 64. That means that every death is responsible for more years of life lost.

http://jodylanard.wordpress.com/ jodylanard

The most blatant of several egregious errors in the PCAST report is its statement that “The case-fatality ratio (i.e., proportion of infected individuals who die as a result of the infection) appears to be similar to seasonal influenza”

CDC data suggest that on average, the seasonal flu has about a 0.1% case fatality rate.

CDC stated on June 26 that there had been “for sure” at least a million symptomatic cases of pandemic H1N1. On that date, they confirmed 127 deaths. (See the CDC telebriefing transcript from that date, on the CDC website.)

These two numbers — “at least a million cases” and “127 deaths” — yield an estimated Case Fatality Rate of less than 0.01 percent — ten times lower than that of the average flu season.

On August 18, the CDC told Wall Street Journal medical reporter Betsy McKay that there have been more than two million cases of pandemic H1N1 in the U.S. As of August 18, CDC confirmed 477 deaths.

The same calculation applied to “more than two million” and “477 deaths” yields an estimated case fatality rate of less than 0.02 percent — five times lower than that of the average flu season.

There are other similarly blatant errors, leading to grossly incorrect assumptions, in the PCAST report. These will be reported out over the next few days.
desiderada

Of course, the public doesn’t get too upset about a 92 year old passing quietly in the night. It’s one less “parasitic” drain on young people’s future and one less competitor for benefits for other old people. I have pretty much the same philosophy toward youngsters passing in the night, even though they’d never dream of going quietly, anywhere. One less competitor for a parking space near the shopping center door, one less racket making, bass throbbing car slowing to a pulsating pause near my house at 3 am, and fewer school buses impeding my movement between meetings for mahjong and chiropractic manipulation. I do have one slight hesitation about working-age adults falling victim to this pandemic. One less person to contribute to my old age pension. Maybe we could double the rate on the ones that are left.
http://www.stockmarketnewz.com/2009/08/25/h1n1-death-projections-doing-the-math/ H1N1 death projections: doing the math

[...] By Laura Blue, courtesy of TIME [...]
clfh

I will pray for you.
enigma704

@jodylanard

The report says that there is a .1% mortality rate among people who are hospitalized, not among everyone who contracts H1N1. So while there are perhaps 2 million people who have shown symptoms, only a percentage of those have been hospitalized and are factored in to that specific mortality rate.
http://olivermark.de/blog/archives/539 alles Unsinn…ich bin müde » Blog Archiv » Schweinegrippe: eine Berechnung

[...] frage mich nur, wie die auf die 50% Infektionsrate kommen, auch wenn die meinen, es wäre “by no means certain”, d.h. überhaupt nicht [...]
http://jodylanard.wordpress.com/ jodylanard

The report states that 0.1% (actually it states 0.1-0.3%) die from the cohort of those that are either hospitalized OR sought primary care — that is, went to a doctor’s office or a clinic.

And the report states that the seasonal flu Case Fatality Rate of “all symptomatic cases” is somewhere between 0.05% and 0.2%.

From the report: The pandemic virus’ case fatality rate “appears to be similar to seasonal influenza—possibly on the order of 0.1 to 0.3 percent of medically attended cases (i.e., those infections requiring hospitalization or primary care), and perhaps 0.05 to 0.2 percent of all symptomatic cases, whether or not medical care is sought”.
http://blog.totallyready.com/?p=1083 Pandemic to Stress Health Care System…Crime Rates Rise | Totally Ready

[...] http://wellness.blogs.time.com/2009/08/25/h1n1-death-projections-doing-the-math/ [...]
http://familypreparednessguide.com/what-will-happen-when-the-flu-epidemic-hits/ What Will Happen When the Flu Epidemic Hits? | Family Preparedness Guide

[...] http://wellness.blogs.time.com/2009/08/25/h1n1-death-projections-doing-the-math/ [...]