GREP Expression help

Sorry to bother, but I'm still struggling with GREP! I need an expression that superscripts the numbers at the start of a string of references - for example:

1Princess Margaret Hospital, Toronto, ON, Canada; 2University of Manitoba, Winnipeg, MB, Canada; 3London School of Economics, London, UK; 4Hospital Universitario 12 de Octubre Madrid, Spain.

The references need to remain a single line,  each reference separated by a semicolon, and the digits can typically include up to 2 characters. As in my example, the names can include digits at times, so those would have to be excluded from superscripting. Help!