Researchers Investigate Effects of Temperature, Air Humidity on Sterility of Wrapped Packages

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In a research brief published in Infection Control and Hospital Epidemiology, Camila Quartim de Moraes Bruna, MS, Flávia Morais Gomes Pinto, MS, and Kazuko Uchikawa Graziano, PhD, of the Department of Medical-Surgical Nursing at the University of São Paulo, acknowledge the numerous recommendations for storage of reprocessed medical devices and instruments to maintain sterility, and that suggested values for temperature and air humidity vary widely.

As the researchers observe, "Most controversies have arisen from studies that have evaluated the sterility of devices stored under different temperature and air humidity conditions, with discordant results. Could temperature and air humidity above the usual recommendations lead to contamination of surgical-package contents? To answer this question, an experiment was designed to determine whether contamination of sterile products occurs when they are stored at high temperature and high air humidity."

Eight metallic boxes containing surgical instruments (eg, clamps), were used as the experimental and control groups. Each of the  boxes contained 30 porcelain cylinder carriers that were attached to the instruments by silk yarn. At the end of the storage period, each carrier was removed and inoculated in culture medium, yielding a total of 240 samples. The cylinders used allow high adherence for microorganisms and are recommended by the Association of Official Analytical Chemists for the evaluation of sterilization processes. Each of the surgical boxes was packed in one of four wrapping materials: a woven textile, a nonwoven textile (SMS), crepe paper, or a plastic pouch, followed by sterilization in a high-pressure saturated steam autoclave at 134°C for 5 minutes. The wrapped boxes were deliberately contaminated on the external surfaces by manipulation with gloved hands that had been immersed in 1 L of broth (Trypticase soy broth [TSB]) containing 106 colony-forming units (CFU)/mL of Serratia marcescens (ATCC 14756). Then the boxes were randomly assigned to experimental and control groups.

After 30 days of storage, boxes from the experimental and control groups were opened in a laminar flow hood, using aseptic techniques. The porcelain cylinders were removed, inoculated directly into tubes with TSB, and then incubated for 14 days at 22°C. The average temperature registered in the incubator for the experimental group was 32.8°C, and the average air humidity was  75.8 percent. After 30 days, none of the tubes with the cylinders showed microbial growth. The average temperature registered for the control group was 21.6°C, and the average air humidity was 68.4 percent; again, none of the tubes showed bacterial growth. All samples from the positive control group demonstrated bacterial growth after the 30 days of incubation.

The researchers note, "The absence of adherence of microorganisms to carriers stored inside the wrapped surgical boxes demonstrates the capacity of the tested packaging to ensure sterility inside the boxes, even in the presence of microorganisms and high temperature and air humidity. These findings reinforce the premise that recommendations from associations and authors may be based on common sense and applications of concepts used in the pharmaceutical and food industries, and not on scientific evidence."

Reference: Quartim de Moraes C, et al.  BrunaResearch Brief: The Influence of Environmental Temperature and Air Humidity on the Maintenance of Sterility of Surgical Instruments Sterilized in Different Wraps. Infection Control and Hospital Epidem.  Vol. 33, No. 12, December 2012. 

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