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Overview :
Richter et al developed an algorithm for evaluating a blood
culture positive for a possible contaminant. This can help optimize use of
laboratory resources by reducing unnecessary testing. The authors are from the
University of Iowa in Iowa City.
Possible contaminant organisms:
(1) coagulase negative staphylococci
(2) aerobic and anaerobic diphtheroids
(3) Micrococcus species
(4) Bacillus species
(5) viridans group streptococcus
Questions:
(1) number of blood culture sets collected within a 48 hour
period
(2) number of blood culture sets positive for the same
organism
(3) organism isolated
where:
• The
timing of blood cultures was based on the time of collection.
• The
number of bottles in culture set was not utilized in the algorithm.
• The
approach differs from the of Weinstein in that coagulase negative staphylococci
are not handled differently.
The isolate was worked up based on an evaluation of the
clinical and laboratory features performed by a pathology resident if:
(1) only 1
blood culture set was taken
(2) more
than 1 blood culture set was taken within a 48 hour period, more than 1 blood
culture set was positive for the same organism, and the isolate was a
contaminant other than viridans streptococcus.
If more than 1 blood culture set was taken within a 48 hour
period, more than 1 blood culture set was positive for the same organism, and
the isolate was viridans streptococcus, then the identification and antibiotic
susceptibility testing is done.
If more than 1 blood culture set was taken within a 48 hour
period, and if these are not positive for the same organism (only 1 culture set
is positive OR different isolates are seen) then:
(1) the
isolate is considered a contaminant and
(2) the
identification and antibiotic susceptibility testing is done only if requested
by the patient's physician.
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