Wilson and Gaido developed a system for interpreting the significance of urine culture isolates. This can help decide if the findings are significant pathogens or contaminants. The authors are from the University of Colorado in Denver.
Parameters:
(1) probability of contamination based on method of specimen collection
(2) number of isolates
(3) colony counts for the isolate(s) in colony forming units (cfu) per mL
|
Method of Specimen Collection |
Probability of Contamination |
|
aspiration, collection in operating room, single straight catheterization, collection from a patient on antibiotics |
low |
|
clean catch urine, indwelling catheter, nephrostomy tube, ileal loop, ureterostomy tube |
high |
|
Risk of Specimen Contamination |
Number of Isolates |
LOG10 (CFU per mL) |
Interpretation |
|
low |
1 |
< 2 |
probable contaminant |
|
low |
1 |
>= 2 |
significant isolate |
|
low |
2 |
both < 2 |
probable contaminants |
|
low |
2 |
one < 2, one >= 2 |
1 contaminant, 1 significant |
|
low |
2 |
both >=2 |
both significant |
|
low |
>=3 |
one >= 5, rest < 5 |
1 significant, others contaminants |
|
low |
>=3 |
all >= 5 |
all contaminants |
|
high |
1 |
< 4 |
problem contaminant |
|
high |
1 |
>= 4 |
significant isolate |
|
high |
2 |
both < 5 |
both contaminants |
|
high |
2 |
one >= 5, rest < 5 |
1 significant, 1 contaminant |
|
high |
2 |
both >= 5 |
both significant |
|
high |
>=3 |
one >= 5, rest < 5 |
1 significant, others contaminants |
|
high |
>=3 |
all >= 5 |
probable contaminants |
where:
• In the original table, for high risk of contamination and 1 isolate, the decision point was 10^2 isolates per mL. This is the same as for specimens with a low risk of contamination. In the discussion on the same page they talked about using 10^4 cfu per mL. I used this decision point instead since it makes more sense to me.
Specialty: Infectious Diseases, Urology
ICD-10: ,
