Well, here is your chance to enlighten us, O wise one.
The exterminator who called in cleared up the things that were setting off alarm bells in my head. I could add a couple of things. Encasing your mattress is a good idea provided you know what it will and won't accomplish. It will trap any bugs who are already in it until they die (NB: This can actually take more than a year!) and will keep any additional ones from getting into it. The primary benefit, though, is that you won't have to replace your mattress. It won't get other bugs so discouraged that they decide to leave your home; they'll just hang out in other places where they may be even harder to locate. For this reason, it's best not to encase your box spring, if you have one. If bugs get into your home, they're going to live someplace, and it's actually better to have them congregate in a relatively confined area (at first--eventually they'll reproduce to the point where they need to spread out. You want to have dealt with them before this point), and the box spring is cheaper to replace than a mattress.
Also, if you think you have the problem licked but aren't sure, or want to know early if they return, there are some monitoring devices you can get that will alert you to their presence in your home. The most sophisticated ones cost hundreds of dollars, but there are also some low-tech ones that are very inexpensive. See the Resources section of bedbugger.com.
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