or....
Code:
Sub Sev_ER()
Dim r As Range
Set r = ActiveDocument.Range
With r.Find
Do While .Execute(findtext:="severe", Forward:=True) = True
With r
.MoveStart 1, 3
.MoveEnd 1, -1
.HighlightColorIndex = wdGreen
.Collapse 0
End With
Loop
End With
End Sub