RESUMEN
The objective of this collaborative work carried out in the Fundación Favaloro and the Fundación para la Lucha contra las Enfermedades Neurológicas de la Infancia, was to determine optimal conditions for incubation (time and atmosphere) of quantitative cultures of catheters processed according to the technique of vortex agitation (Brun Buisson method). From 689 processed catheters, 551 yielded negative cultures. From the 138 positive cultures, 125 yielded monomicrobial cultures and 13 polimicrobial cultures (total number of microorganisms was 151). In the last situation each micoorganism was considered on an individual basis. A total of 58 episodes of catheter related bacteremias occurred, being 52 monomicrobial and 6 polimicrobial (total number of microorganisms was 64). When colony counts were compared in aerobic and in 5-10 CO2 atmospheres, a very good correlation was obtained (p = 0.27; r2 = 0.9268). No advantage was observed by incubating plates for more than 48 hours. Colony counts performed at the second versus the third day, and at the second day versus the seventh, gave very good correlation (p = 0.10 and r2 = 0.9996; p = 0.31 and r2 = 0.9995, respectively).