The European Tissue Symposium has developed a Position Paper and additional documents which compares the different Hand Drying Systems.
This Position Paper is compact but very comprehensive summary of the numerous and extremely important studies which have been held around the world comparing the hygiene aspects of using Paper Towels or Electric Hand Dryers.
Some of these studies has been sponsored by ETS, some is totally independent. 
The Position Paper below is a very powerful and useful reference for those who needs to decide about the Hands Drying system to be adopted in their facilities.

Previous releases of this Position Paper are available also in other Languages:

Italiano:     Presa di posizione sull’uso di asciugatori elettrici ad aria rispetto agli asciugamani di carta (Nov 2015)  

Español:    Posición en el uso de secadores de aire eléctricos frente a las toallas de papel (Nov 2015) 

Deutsch:    Standpunkt zur Nutzung von Papierhandtüchern versus elektrischen Lufttrocknern (Nov 2015)  

In addition to the links below, ETS suggest the studies listed in the page