modifying search

I’m not familiar with the WordPress code that controls search, but have you tried searching for the phrase in quotes? “cabin fever”

There’s a post by Lorelle that talks about replacing the built-in WordPress search functions with a search engine search function, but a search engine search function might not give you exactly the control you want.
http://lorelle.wordpress.com/2006/02/11/understanding-and-fixing-wordpress-search/

If you’re into programming php, you could try starting with an existing plugin to see if you can modify the code to limit the search to the exact string entered, but modifying or creating a plugin like that would take a lot of php and MySQL know how. Here are a few search-related plugins and plugin documentation.
http://ww.wp.xz.cn/extend/plugins/search-everything/
http://ww.wp.xz.cn/extend/plugins/search-unleashed/
http://codex.ww.wp.xz.cn/Writing_a_Plugin

If you’re not into php programming, you might be stuck with the search the way it is.