Explain xkcd: It's 'cause you're dumb.
The number of germs that would be left after using the hand sanitizer is 200 million times 0.01%. 0.01% is equivalent to .0001 decimal, so the simple equation is 200000000 × .0001. That equals 20 thousand germs, which is still a surprisingly large number of germs.
Note that in some simple / business calculators entering the calculation as "200000000 × 0.01 %" is incorrect and may produce number such as 2 million. Pressing "=" after may also be incorrect and may produce 400`000`000`000`000. This is because the "%" key in those calculators does not denote that preceding number is a percentage, but instead signify an operation related to percentage, for example some calculator the "%" key will replace the preceding number with that number as percentage multiplied with the number before that (How does the calculator percent key work? - The Old New Thing).
Side note - Recently scientists have shown that it only takes 20 virus particles to infect someone  (with analyzed virus: not all germs are equally effective). They have also previously noted that the effectiveness of hand sanitizer is actually higher than 99.99%, it's just awkward to print a more precise decimal in an advertising slogan.
"Hipster CDC" is a combination of the acronym for the Centers for Disease Control and Prevention, an organization dedicated to studying infectious diseases and limiting their spread, with the label hipster. Hipsters form a cultural group associated with a distaste for popular culture; they stereotypically talk about how bands, authors, etc... were better before they went "mainstream" and proclaim that they liked a certain thing "before it was cool". The humor lies within the idea that the Hipster CDC and Hipsters would most probably have not used common anti-bacterial medicines such as hand sanitizer. As such, the minuscule changes caused by these tools in prevention of the flu would never have taken effect on hipster culture, which would be exposed to the full brunt of the flu epidemic from the very beginning. Hence, the flu epidemic "peaked" within that community from the very beginning.
In this case, the period when the flu epidemic was "better" is probably 1918, when a world-wide flu epidemic killed tens of millions..
The humor (if a worldwide disaster can be said to be humorous) is in the dual use of the word "epidemic". The current mainstream news media is making a big thing of an up-surge in flu cases this season, sometimes calling it an "epidemic". The comic points out that, in reality, the worldwide flu epidemic is an on-going, multi-year thing, and the current seasonal up-surge is tiny and uninteresting in comparison to previous surges.
- Poster: An invisible sneeze droplet can contain 200 million germs!
- Product label: Our hand sanitizer kills 99.99% of germs!
- Cueball (typing on calculator): 200 000 000 × 0.01% =
- Cueball: Ew.
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Does anyone think the "peak" referred to in the title text could be the 1918 flu pandemic? Or even the bird flu outbreak?Chexwarrior (talk) 10:31, 16 January 2013 (UTC)
- I'm thinking the "hipster" comment is a reference to how hipsters always think stuff was better (or it peaked) in the past so it must be on the downslide.--Joehammer79 (talk) 14:47, 16 January 2013 (UTC)
That 99.99% number on the hand sanitizer is probably made up anyway. Any actual scientific measure of effectivity would need to take into account different resistance of different types of germs. So, question is, is the sanitizer more or less effective? -- Hkmaly (talk) 10:35, 16 January 2013 (UTC)
- I actually had in the back of my mind that the 99.99% figure wasn't a "dead germ count," but the number of strains of germs the sanitizer has the ability to kill. i.e. there are some strains which it doesn't kill. —126.96.36.199 12:59, 16 January 2013 (UTC)
- Actually 99.99% isn't made up, its actually derived from how accurate the lab tests are. Most antibacterials, even plain 15% alcohol, will kill ALL infectious bacteria and viruses but you cannot confirm this because there are errors inherent in the tests such as contamination from the environment or more often that the samples have to grow (in the case of bacteria) or infect (in the case of viruses) to give a measurable result since you cannot tell by normal observation which are dead and which are live. With the tiny numbers that may survive the likelihood of infection or growth is low, resulting in errors with even the strongest chemical agents. --188.8.131.52 18:56, 16 January 2013 (UTC)
- 15% alcohol is hardly effective (please state source), most effective is 70%, which means anything lower doesn't kill all bacteria. Alcohol is also only partially effective against viruses. It needs other agents to boost its effectivity. 184.108.40.206 09:27, 17 January 2013 (UTC)
Shouldn't 200 million times .01% actually be equivalent to 200 million times .0001, which equals 20 000 germs? 220.127.116.11 13:16, 16 January 2013 (UTC)
- The error depends on the calculator, I think. In my calculator 200000000 ✕ 0.01% = 20000 - Arifsaha (talk) 17:38, 17 January 2013 (UTC)
Yes, it should. I wonder if he will change it when he notices? 18.104.22.168 13:37, 16 January 2013 (UTC)
Yes, 2 000 000 * .01% = 20 000 is correct
- ... Except that the calculation should be 0.01% of 200`000`000 - Arifsaha (talk) 17:38, 17 January 2013 (UTC)
- It is perfectly fine to write 200000000*0.01%. "%" is simply shorthand for 1/100. 09:30, 6 November 2015 (UTC)
Quite aside from the arithmetic, right now the US has two epidemics: influenza and norovirus, which is often known by the misnomer of "stomach flu." According to infectious disease experts, while alcohol is likely pretty effective against bacteria and SOME viruses including influenza, alcohol is probably NOT very effective against norovirus. The best way to stop the spread of norovirus: frequent hand washing with soap and water.
22.214.171.124 13:47, 16 January 2013 (UTC)
- I'm sure that it will not stop people from trying to use alcohol to get rid of norovirus infection. :-) -- Hkmaly (talk) 11:05, 7 March 2014 (UTC)
"The humor (if a worldwide disaster can be said to be humorous)" I found this funnier than the comic, really. 126.96.36.199 04:17, 21 January 2013 (UTC)