The most appropriate word for use in the example sentence is [*'absenteeism'*](http://www.merriam-webster.com/dictionary/absenteeism), although I would argue that, considering the meaning of 'absenteeism', 'absence' would not be inherently wrong (with the sidenote that 'absenteeism' is perhaps less..ambiguous).

That said, 'absence' indicates a person's non-presence, there is no plural form of *'absence'* to describe the fact that he, a single individual, is away, as far as I have been able to determine.

[Wikipedia](https://en.wikipedia.org/wiki/Absenteeism) also holds some good information on the word and its usage.

Looking at *'absence'* [here](http://dictionary.reference.com/browse/absences), under "Examples from the Web for absences", context appears to clearly show that absences is used to refer to the number of times or instances non-presence was observed.