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, which shows you the hot search queries on Google at any given time, is more than two years old now (this year they added website/domain tracking as well). PR professionals and brand managers use it regularly to track how hot their assets are, and there are countless other uses for the service.

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: