In Admin > Settings > Email > Sickness Alerts the sickness levels which once reached would send an alert email can be setup.
The sickness levels are measured by the Bradford factor which calculates its measurement by Total Incidents X Total Days X Total Days in both a 12 month and 13 week period. So if you consider 4 sickness incidents comprising 2 days each to be excessive in a year then the Bradford factor to watch for would be 4 x 8 x 8 = 256.
The emails which receive this sickness alert notification can include real email addresses or markers for relative ones such as #MGR_Email# which is the employees manager. Email addresses should be separated with a semi colon (;).