Over the past 72 hours, swine flu has become one of the most important "unknowns" hanging over the global financial markets. But how much of an impact will swine flu really have? To gauge its impact on the broader markets, Jason Goepfert of the Sentiment Trader blog has dug into the archives to review the data on the behavior of the S&P 500 around the time of the outbreak of the SARS virus in 2002-2003:

"While the consequences of the Swine Flu outbreak is tragic to those dealing directly with the outbreak, investors should take a step back and wonder about the correlation to equities. Some stocks will, of course, directly suffer or benefit depending upon their business model.  And perhaps, if this gets worse, it could impact the worldwide economy.  But we went through a very similar exercise 6 years ago with the SARS outbreak. The chart [above] shows the timeline of the SARS panic along with the price chart of the S&P 500.  Draw your own conclusions about correlation."

That being said, it looks like the S&P 500 dropped when the first SARS cases were announced, and proceeded to fall more as it became an international outbreak. Within a few months, though, the market proceeded again on an upward trajectory. What's interesting to note is that the stock market began to rebound before the full panic subsided -- not after.

What do you think? Which stocks or sectors will manage to shrug off the impact of the swine flu?

[chart: SARS and the S&P 500]

Given what we learned during the SARS outbreak, this time around things should move more quickly and in reality, unless a stock is directly tied to Mexico, (travel, food companies present there, etc.) I don't see it having much long term affect. The other side of this is that we are already low historically speaking which was not the case during SARS.

It really depends how severe the outbreak is (if any). If it reaches pandemic proportions, here are a few numbers compiled by The Telegraph, UK - http://www.telegraph.co.uk/health/healthnews/5228878/Estimates-of-economic-costs-of-a-flu-pandemic.html

*The World Bank estimated in 2008 that a flu pandemic could cost $3 trillion (£2 trillion) and result in a nearly 5pc drop in world gross domestic product. The World Bank has estimated that more than 70m people could die worldwide in a severe pandemic.

* Australian independent think-tank Lowy Institute for International Policy estimated in 2006 that in the worst-case scenario, a flu pandemic could wipe $4.4 trillion off global economic output.

* Two reports in the United States in 2005 estimated that a flu pandemic could cause a serious recession of the US economy, with immediate costs of $500bn-$675bn.

* SARS in 2003 disrupted travel, trade and the workplace and cost the Asia Pacific region $40bn. It lasted for six months, killing 775 of the 8,000 people it infected in 25 countries.

Egypt is slaughtering all hogs. Who will follow? Who will benefit?