On October 11, 2007, the National Library of Medicine (NLM) released a new search engine for MedlinePlus, MedlinePlus en español and the NLM Web site. NLM selected search engine software from the Pittsburgh-based company Vivisimo. Vivisimo is also the current search solution for the USA.gov site (formerly FirstGov).
The new search results feature enhanced relevance rankings and bold-face search words in context to help you select the best Web document for your query. An integrated spell checker suggests alternative search terms and spelling corrections. The new search engine also expands queries using synonyms specific to the sites and medical synonyms from the NLM Unified Medical Language System.
For more information, please see the NLM Technical Bulletin: http://www.nlm.nih.gov/pubs/techbull/so07/so07_nlm_search_engine.html