Earlier today, the U.S. declared a public health emergency over the Swine Flu, after confirming 20 cases of the flu spreading to humans in New York, Ohio, Kansas, Texas and California. More than 80 people have died in Mexico from the disease, which has potentially spread to other countries, including Canada and France. Although Federal officials are urging Americans not to panic about the disease, fear of contracting the potentially deadly flu is quickly spreading over Twitter, Google, and blogs across the web.

Swine Flu is the top trending topic on Twitter at the moment, with users rapidly tweeting about the latest news about the disease, including whether it has spread to other states, the Center for Disease Control’s announcement, etc.

Google Trends reports that “Swine Flu Ohio” is the 27th most popular search keyword currently, with searches for the “CDC” and “Swine Flu Symptoms” also making the top 100 keyword searches on Google.

Google Maps have also been created to chart the spread of the Swine Flu. Below is a Google Map created by a bio medical engineer, that charts suspect and confirmed cases of the Swine Flu in the U.S. and Mexico.

Technorati’s index, which graphs the number of times the search term occurs in blog posts across the web, shows that mentions of Swine Flu in blog posts has risen sharply from Friday to nearly 2800 blog post mentions today.

Keyword popularity across the Blogosphere

This chart illustrates how many times blog posts across the Blogosphere contained the following keywords.

swine flu

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One use though, which is becoming increasingly popular we hear, is for blogs, mainstream media sites and others to monitor Google Trends regularly and write stories based on hot terms. Google displays a daily summary for easier data gathering.

The goal isn’t to tap into what Internet users think is interesting and write about that. Instead, it’s all about getting more hits from Google.

Here’s how it works:

Blogs and mainstream media sites are indexed by Google very frequently. Many times per day, in fact. And those sites often have great Page Rank already. Combine that regular indexing and Page Rank with Google’s recent policy of ranking news type results higher than older, evergreen stuff, and you have a system ripe for abuse.

Let’s say I run a popular political or celebrity gossip site (two topics that pop up a lot on Google Trends). I look for hot queries that people are typing in right now, for whatever reason. Then I write a blog post, making sure to use the query term in the title of the post (which weights heavier for matching content to specific queries). The content of the article itself is mostly irrelevant, as long as your normal readers don’t gag on it.

Within a few minutes that content is indexed by Google, and the high Page Rank of the site along with the newness of the content pushes it up towards to top of the first page of results. Possibly all the way to the top.

We’re not talking about a trivial amount of traffic, either. One person I spoke with about this yesterday said he can get up to 30,000 extra unique visitors per day just by focusing content on top queries, which is more than enough to dedicate a couple of full time people to the effort.

I’ve debated (with myself) on how “bad” this kind of behavior really is. Sites that do this are clearly exploiting a weakness in Google’s search methodology, but it’s not like they’re engaging in black hat SEO tactics to trick Google into thinking their content is more relevant than it is. Rather, they’re just using their Page Rank heft and cheating a little on the edges.

I’m not going to say which sites I’m hearing are doing this, but you can check for yourself. If you see a headline that seems a little off topic or weird, followed by some very hastily written content, have a quick look at Google Trends and see if the exact query is in the title of the post or article. You may be surprised at who’s taking advantage of this.

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Up to five terms can be compared. And you can also view queries that contain either or two terms, using a vertical bar “|”. More advanced queries can be done as well – see the FAQs for details. Google also puts markers next to major news events that are about that search query, helping to explain surges. Data can be sorted by time, language, geographic location, etc.

In testing it I’m finding it works well for very highly searched terms, but terms that are very rarely searched show no data at all. Seeing trends on even obscure terms would be useful. Even so, Steve Rubel says Google Trends is “a must-bookmark for every PR person and marketer worldwide.”