Weinstein uses a system for evaluating a blood culture that is positive for a possible contaminant. This can help minimize the costs associated with unnecessary laboratory workup or therapy for a patient. The authors are from the Robert Wood University Hospital in New Brunswick, New Jersey.
Possible contaminant organisms:
(1) coagulase negative staphylococci
(2) aerobic and anaerobic diphtheroids
(3) Micrococcus species
(4) Bacillus species
(5) viridans group streptococcus
Usually a contaminated blood cultures will involve only a single blood culture will be positive out of several sets drawn. With endocarditis or other bloodstream infection all or most of the cultures taken will be positive.
|
Number of Cultures Submitted
|
Number Positive
|
Workup
|
Report
|
|
>= 2
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1 for possible contaminant
|
none
|
isolate reported as being a probable contaminant
|
|
1
|
1 for possible contaminant
|
none unless requested by patient's physician
|
isolate reported as being of indeterminate significance
|
|
>= 2
|
>= 2 for possible contaminant other than coagulase negative Staphylococcus with 48 hour period
|
complete
|
If the isolates are different then they are reported as probable contaminants without susceptibility results. If the isolates are the same, then the speciation and susceptibility are reported.
|
|
>= 2
|
>= 2 for coagulase negative Staphylococcus with 48 hour period
|
complete
|
If the isolates are different then they are reported as probable contaminants without susceptibility results. If the isolates are the same, then the speciation and susceptibility are reported.
|
where:
• The workup consists of speciation and antibiotic susceptibility testing.
• Isolates are considered probably identical if both the biochemical profiles and susceptibility patterns are the same.
• Molecular techniques are required to confirm that multiple isolates of the same species are truly identical.
• Rarely patients may have true bacteremia with polyclonal coagulase negative staphylococcus species. If the patient has clinical sepsis and no other cause is found, then it is appropriate to report the antibiotic susceptibility results.
• Not all possible combinations are covered in this table. For example, the presence of multiple different isolates of possible contaminants in the same culture would favor contamination.
