WebProNews

Health related Web sites remain popular. An average of 55.3 million U.S. Internet users visited health information Web sites each month during the first quarter of 2007. That is a 12 percent increase over the same period in 2006, according to comScore.

WebMD Health had the most traffic with an average of 17.1 million unique visitors per month. NIH.gov was second with 9.8 million monthly visitors. MSN Health had 8.1 million visitors and Yahoo Health had 6.7 million monthly visitors on average.

"While the larger and more established health portals are continuing to grow, the category is being shaken up by a few upstarts," said Carolina Petrini of comScore.

"In the past year, both Healthline.com and QualityHealth.com have more than doubled their respective online audiences to nearly three million visitors per month, becoming major players in the category."

Visitors to health related Web sites are also loyal. Only 16.8 percent of MSN Health users visited other health sites. A fifth or less Yahoo Health and Healthline.com users visited other health sites.

The most searched keyword, "pregnancy," was entered over 17 million times in the first quarter of 2007. "Cancer," "flu" and "fitness" each had 15 million searches.