Generally, it is true that filtering viruses is less of a concern in the US than globally, especially in the back country as opposed to more populated areas. That isn't to say that there isn't the possibility of catching a virus in the US, but it is less of a concern than in areas with less sanitation. If you are particularly concerned about viruses, you can filter then disinfect, or use a water purifier rather than a water filter.
Generally, heavy metals are not a concern in the US, but it is possible for areas nearby an old mine to have higher levels, for example. You aren't likely to have an easy way to filter those out in the back county, anyways, so checking the history of your destination would probably be more effective.
I wouldn't be too concerned about filtering viruses unless you are going to be in a lower-lying area that is more heavily populated, and wouldn't worry about heavy metals unless you are going to be in an area nearby an old mine. If you are particularly concerned about the former, consider a water purifier or a two-step filter-disinfect process, by filtering then adding tablets or filtering then boiling, but it's not usually necessary.