Blood Culture effect

Stepped out of M&M (Morbidity and Mortality Conference) for a second to get this one out...
I am sure there is a better name for this in the quality/process improvement literature, but there is a strange phenomenon in medicine where we react all aggresively to the notification that blood cultures have turned positive.
To give you a little background- blood is taken from ill patients in whom we suspect infection, and grown on culture media (think buffet for bacteria).  In the next 12-36 hours, bacterial colonies will grow (if present in the blood) and become large enough for us to see, identify and test.  By the way folks, that's why blood cultures take so long to come back relative to other tests, the things have to grow.
Anyway, it is common practice to receive a call from the Micro lab that your patient's cultures are positive for something.  Upon getting this news, the typical thing to do is have a small moment of panic, then go check on the patient.  Now, think this one through.  The blood was taken 2 days ago.  They have been fine/stable/sick the entire time.  But now that we have received the information, we are all of a sudden worried.
I am unsure why this phenomenon exists, but it seems that alarm bells bother us because they are sometimes all we have to know that a system is malfunctioning---even though it has been doing so for the last two days!  Illogical, yes, but I also wonder how responsibility/liability comes in, because positive blood cultures tend to become a hot potato.

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