A prospective, randomized, and comparative study of 3 different methods for the diagnosis of intravascular catheter colonization.
BACKGROUND
Demonstration of catheter tip colonization is usually performed by use of Maki's semiquantitative technique, although the superiority of quantitative techniques has been claimed on the basis of their purported ability to detect both endoluminal and exoluminal microorganisms.


METHODS
We prospectively compared Maki's semiquantitative technique and the quantitative methods of sonication and vortexing for the detection of colonization of intravascular catheter tips and catheter-related bloodstream infections. All 3 techniques were performed on the tip of each catheter, and the order in which each technique was performed was randomly assigned.


RESULTS
Of the 1000 catheter tips that were processed, 329 (32.9%) had positive results for at least 1 of the 3 techniques when a breakpoint of >or=100 colony-forming units (cfu)/catheter segment was used for the quantitative techniques and a breakpoint of >or=15 cfu was used for Maki's technique. Eighty-two of the catheter tips for which results were positive were from patients with catheter-related bloodstream infections. For each technique, the likelihood of detection decreased progressively depending on the order in which the technique was performed (i.e., second vs. first and third vs. second). The likelihood of detection of catheter colonization for each technique, when the technique was performed first and when 2 breakpoints (>or=100 cfu/catheter segment [criterion B] and >or=1000 cfu/catheter segment [criterion A]) were used for the quantitative techniques and a breakpoint of >or=15 cfu was used for Maki's technique, was as follows: 99.1% and 100% for Maki's technique, 95.1% and 92.9% for sonication, and 93.1% and 72.8% for vortexing (for criteria B and A, respectively). No inferiority of Maki's technique could be demonstrated when results were compared according to whether catheter placement was short term (i.e., <7 days) or long term (i.e., >or=7 days), either for the detection of colonization or for the detection of catheter-related bloodstream infections.


CONCLUSIONS
According to data from the present study, the quantitative techniques of sonication and vortexing were not superior to Maki's technique under the test conditions used. The greater simplicity of Maki's semiquantitative technique makes it the procedure of choice for routine work in the microbiology laboratory.
Bouza
Emilio
E
Clinical Microbiology and Infectious Diseases Department, Hospital General Universitario Gregorio Marañón, Madrid, Spain.
Alvarado
Neisa
N
Alcalá
Luis
L
Sánchez-Conde
Matilde
M
Pérez
María Jesús
MJ
Muñoz
Patricia
P
Martín-Rabadán
Pablo
P
Rodríguez-Créixems
Marta
M
D001424:Bacterial Infections / Q000175:diagnosis*; D002408:Catheters, Indwelling / Q000382:microbiology*; D004866:Equipment Contamination; D006801:Humans; D011237:Predictive Value of Tests; D012680:Sensitivity and Specificity; D013010:Sonication