One of the reasons flu is so closely watched is because of the huge number of humans who come down with it every year. A small change in mortality rates (the percentage of people who die from a disease) can have a huge impact because the numbers are so large.
In an average year, according for the Centers for Disease Control (CDC), between 5 and 20 percent of the U.S. population comes down with the flu. For the purposes of this calculation let’s say it is halfway: 12.5%.
Twelve and a half percent of the U.S. population is about 37.5 million.
The CDC also reports that 200,000 people are admitted to hospitals in the U.S. for flu or flu-like symptoms every year.
Other researchers have calculated that on average, about 40,000 people die in the United States each year from the flu or complications of the flu. As a comparison, According to the CDC about 650,00 die from heart disease and about 550,000 die from cancer. Every year.
If 40,000 people die out of the 37.5 million who come down with the flu that is a mortality rate of a little over one tenth of one percent.
According to a Stanford University summary of the great flu pandemic of 1918, the mortality rate in that outbreak was about 2.5 percent – almost 25 times the mortality of a normal flu year.
So, to complete the discussion, if this Swine Flu has a higher than normal mortality rate, maybe even as high as 2.5%, and a normal number of Americans – 37.5 million – are infected with it then over 950,000 Americans would die of that flu strain.
If contagion rates are higher than average and this strain of flu is as virulent as the 1918 strain then well over a million Americans might die of it.
In Mexico, as of yesterday, 1,300 people had contracted the disease and 80 had died – a mortality rate of over 6 percent.
Hence, the concern.
via CNSNews.com – Don’t Cry for Me Influenza.
Still unexplained numbers from Mexico–wikipedia has 1626/48 deaths which is lower mortality than numbers that you have but still high. But according to the CDC’s MMWR there are over 10k suspected cases in Mexico which would bring down the mortality % to what we are seeing worldwide thus far-about 1% or less.
The problem with your mexico city example with mortality is that you are not commparing the number infected to ILI deaths but the number hospitalized. If for example the hospitalization rate is 4% of those infected, and 1200 hospitalized we are looking at 300,000 possible infections, hence the mortality rate will be much closer to a seasonal flu epidemic than an Ebola like outbreak!