The effect of temperature on bactericidal properties of 10% povidone-iodine solution

Objective: Ten percent povidone-iodine (PVI) is commonly used as a bactericidal solution before amniocentesis is performed. Warming PVI may increase patient comfort; however, the effect of warming on its bactericidal properties is not known. The objective of this study was to determine the effect of warming 10% PVI on its bactericidal properties. Study Design: Room temperature of PVI was 25°C, and temperature in an ultrasonic gel warmer was 32°C. In vitro experiments were conducted in 25°C and 32°C water baths. Nine milliliters of PVI at each temperature was added to 1 mL of bacteria (107 organisms/mL Staphylococcus aureus, Enterococcus species, Escherichia coli, group B Streptococcus). After 0.25, 0.5, 1, 2, 4, and 8 minutes, 1-mL samples were removed and added to 4 mL of 0.5% sodium thiosulfate (to neutralize the iodine and interrupt bactericidal action). The number of viable organisms was determined by plating 0.1-mL samples on trypticase soy agar plates. Plates were incubated at 37°C for 24 hours and colony-forming units (CFUs) were counted. For in vivo experiments in 40 volunteers, a 9-cm2 area of the dorsum of each hand was wiped with a sterile cotton swab to obtain a sample of bacteria for culture. The area was then wiped for 15 seconds with PVI at 25°C or 32°C and recultured. The bactericidal properties of PVI at each temperature were compared. The Mann-Whitney U test was used as appropriate, and P< .05 was considered significant. Results: In vitro, PVI was bactericidal against E coli, S aureus, Enterococcus species, and group B Streptococcus within 0.25 minutes at both 25°C and 32°C, with median bacterial growth of 0 CFU/plate for each species of bacteria studied (3 replicates at each temperature). Median bacterial growth from skin was 4 CFU/plate (range, 0 to >100). After hands were wiped with PVI at 25°C and 32°C, median bacterial growth was 0 CFU/plate (range, 0-8) and 0 CFU/plate (range, 0-15), respectively (not significant). Conclusion: PVI is as effective at 32°C as it is at 25°C. Use of PVI at 32°C should be considered to increase patient comfort in procedures performed without the use of anesthetics. (Am J Obstet Gynecol 2002;186:869-71.)