I have alarms comin in with the parameter description containing XXXXXX or YYYYYY

I want to filter these using Reg Ex . I have tried the following:-

^(?!(XXXXXX|YYYYYY))

(XXXXXX|YYYYYY).*\s+\1(\s+|$)

and others..

So Alarm A comes in with the field Parameter.Description = 'XXXXXX'

then Alarm B comes in with the field Parameter.Description = 'YYYYYY'

the Alarm C comes in with the field Parameter.Description = 'ZZZZZZ'

So I want to use a reg ex to filter on the XXXXXX or YYYYYY only.