Help with transform

I have a transform for in SNMP trap that will show me the outbound queue of our barracuda with the message count as part of the summary line. The problem is that when the message count changes a new event is created versus updating the existing. Does anyone have an idea how I can handle this Perhaps as part of the transform I can clear previous alarms then write the new trap

Here is what I currently have:

if evt. eventClassKey == "barracuda.2.1.9":
evt.summary = "Outbound mail queue is high" + str (getattr(evt, "barracuda"))
evt.message = "Outbound mail queue is high - " + str (getattr(evt, "barracuda"))
evt.component = str (getattr(evt, "device_title"))