[Comparison of five methods of disinfection of disposable Petri dishes]

The use of disposable materials in the clinical laboratories has significantly reduced the use of glass and other reusable materials, due to their low cost. However, the increase in its price has demanded to reuse them in laboratories from developing countries. The purpose of this prospective and parallel trial was to determine the efficacy of disinfection of five procedures among 7088 Petri dishes (PD) filled with selective media for Gram negative organisms (MacConkey, XLD and Salmonella-Shigella agar) in comparison with 2150 new PD. The first procedure was a strong washing with detergent (1821 PD); the second was the same method followed by immersion in a warm (50-60 degrees C) sodium hypochlorite solution (0/6%) (2127 PD); the third was similar to the former and followed by microwave irradiation at 700 watts for 15 min (1542 PD); the fourth was a rinse with warm (50-60 degrees C) tap water followed by microwave irradiation (958 PD), and the fifth was a rinse with warm tap water (640 PD). The following results were obtained: the rate of contamination was 0.165, 0.2, 0.07, 0.8, 1.4 y 0, respectively; the cost of labor on 1000 PD 10.7, 15.8, 22.4, 9.3, 2.7 y 103.5 US dollars;the initial investment 136.7, 139.5, 623.5, 613, 128.7 y 103.5 US dollars; the time of performance (hours) 5.5, 9.8, 18.3, 13.5, 5 y 0; the number of reused PD to amortise the initial investment 1324, 1350, 6038, 5937, 1247 and no value; and the saving per thousand PD was 92.5, 82.5, 80.7, 93.9, 100.4, and 0 US dollars. Our data show that: procedures 1,2 and 3 were more efficacious than procedures 4 and 5 (p is less than 0.001); although, the third procedure had less contamination the initial investment and the small potential saving do not support its use, and the first and the second methods may be reliable procedures for disinfection of PD as part of a program of reusing disposable medical devices.