You are welcome Mark!
The current market of viable search plugins is pretty much limited to a few good ones, all others miss something vital.
To limit the search to a specific subset of pages, you should start with the General Options -> Sources panel. There you can turn off the search in posts first, as you don't need those for page search – I see you have the diseases on separate pages by starting character.
Then here comes the hard part: Since pages can't have any categories nor any taxonomies, the only way to exclude the rest of them is one-by-one by their ID's – On the Advanced Options -> Content panel, with the “Exclude Posts/Pages/CPT by ID's (comma separated post ID-s)” option.
That might be time consuming, but there is no other way for pages – since you cannot catgorize them by default in WordPress.
I'm from Europe, Slovakia to be exact 🙂Best,
If you like my products, don't forget to rate them on codecanyon :)