Google is expected to announce today the launch of Google Health, a vertical search engine for health and fitness topics, though Google has thus far refused to confirm speculation on several blogs regarding the service, writes MediaPost. The service would compete with Yahoo Health and MSN Health. Screenshots posted on blogs point to coverage of six health-related categories.

The treatment, research papers, "from the medical establishment," symptoms, news, and alternative medicine categories seem to be aimed at consumers; others seem directed at health professionals. The screenshots show search results pages accompanied by keyword ads.

According to clickstream data from Hitwise (see graphic), in April some 2.67 percent of Google's downstream traffic went to sites in the Health & Medical category. Yahoo Search sent 2.43 percent of its traffic to this category, while MSN Search sent 1.97 percent. In short, Health would be a smart vertical initiative for Google.