Jim Vickroy at Memorial Medical Center [where?] asks:

>>We are reviewing our procedures and have a procedure that we really haven't 
been following. This is a procedure that calls for processing possible TB 
tissue by hand. This was based on an old report that possible TB bacteria could 
survive formalin fixation. Right now we are processing all of our tissue by 
automated tissue processors, and we really only handle CJD tissue differently 
than the others. Obviously we don't have many cases suspected of TB but we do 
occasionally process granulomas that are suspicious for AFB positive organisms. 
The final diagnosis of these organisms is usually not known until long after=20
the processing.<<

Acid-fast bacilli are killed by formaldehyde fairly quickly, though as always 
cutting thin and fixing overnight provides an extra margin of safety. Hand 
processing of infected tissue is unnecessary. In at least half of cases a 
pathologist sees, the diagnosis of acid-fast disease wasn't suspected before the 
slides arrived. I think you should change your procedure.

A question I've never gotten an answer to: is human tissue from AIDS patients 
with Mycobacterium avium-intracellulare (MAI) infection a satisfactory 
control for Mycobacterium tuberculosis stains?

Prions in Creutzfeldt-Jakob disease and other prion diseases, as is well 
known, survive both formaldehyde and paraffin. Ordinary hospital pathology labs 
probably shouldn't process prion-infected tissue at all. I think that specialty 
labs do process it by hand. What are the veterinary labs' policies for bovine 
spongiform encephalopathy (mad cow disease) and chronic wasting disease of 
cervids?

Bob Richmond
Samurai Pathologist
Knoxville TN
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