Sorry, no. For a few reasons. First off, harmtouch is disease based. Not fire based, which this effect works on. Secondly, harmtouch is not a spell you could scribe in your spell book. So, it wouldn't be effected by this focus even if harmtouch was fire based.
HT is magic based, with serious resist adjustment. And it IS affected by focus item, if you are over level 44, you need inc dmg III focus for it to work. If over 60 ID 4.
Actualy an ID 1 item will always efect Harm Touch. Harm touch is counted as a level 1 spell no mater what level you are. It is Magic based HT-Magicunless you use your disablin you get a 54-55 then it is disease HT-Disease IF you use your disaplin to increase your damage output and have a MAGIC only improved damage focus, then no added damage will be done. If you have a basic ID (1,2,3,4) ID 4 item then you will get 1- 20% more damage on all DD spells including any type of HT you do. For Sk's, you are beter off just consitrating on an ID item and let the slightly better ones go to the DD classes.