This is one of those stories that sounds scary as heck, but really isn’t telling us anything of consequence. If you haven’t heard, some researchers cultured material from showerheads and found high levels of the atypical bacteria Mycobacterium avium intracellulare, or MAI, living there. This isn’t very shocking as MAI is a water loving organism.
Anyway the important point here is that MAI is not very pathogenic. Even if you’re exposed to it, the likelihood of it causing clinical disease is exceedingly low. If you have a very weakened immune system, like late stage HIV or post-chemotherapy, you might take notice, but for the vast majority of us this is a non-issue.