English to German Medical Medical: Pharmaceuticals clinical studies

Es geht um das Personal oder die Einrichtung?, die das Prüfpräparat verabreicht:

In xxx study drugs was administered by 4 different operators
Of the 106 doses administered (to 54 subjects in Period I and 52 subjects in Period II), 83 were given by 1 operator and the remaining doses were given by 3 other operators (7 or 8 doses each); the operator was unknown on 1 dosing occasion.

Dachte an Bedienpersonal? Betreiber? Laboranten? Aber nichts erscheint mir richtig.