Share thisThe George D. Widener Large Animal Hospital (Figure 1) is one of the largest equine hospitals in the United States, serving nearly 6,000 patients yearly. This hospital also serves as an integral part of the University of Pennsylvania’s School of Veterinary Medicine and is located at New Bolton Center, Kennett Square, PA.
CASE STUDY:
Chlorine Dioxide Gas Decontamination of the University of Pennsylvania’s George D. Widener Large Animal Hospital Intensive and Neonatal Care Units
After a salmonellosis outbreak, the 170,000 cubic foot C. Mahlon Kline building remained under quarantine until a successful decontamination program was implemented
The George D. Widener Large Animal Hospital (Figure 1) is one of the largest equine hospitals in the United States, serving nearly 6,000 patients yearly. This hospital also serves as an integral part of the University of Pennsylvania’s School of Veterinary Medicine and is located at New Bolton Center, Kennett Square, PA.
A salmonellosis outbreak was detected in March 2004. During the following months, multiple cases of salmonellosis were found among the animal population and Salmonella Newport was identified as present in each of these cases. Following this, it was deemed necessary to quarantine the entire Widener Hospital in May 2004 until the adverse bacterial population could be brought down.
The contaminating agent was identified as a multi-drug resistant form of Salmonella Newport, a gram-negative, non-spore forming bacteria. Decontamination efforts were made throughout the Widener Hospital. Several attempts were made at decontaminating the facility (see Figure 2) using a broad-spectrum liquid disinfectant (Virkon S). This solution containing potassium peroxomonosulfate, sodium dodecyclbenzenesufonate, and sulfamic acid (Virkon-S), which is an AOAC approved oxidizing detergent sanitizer, was applied on most surfaces following manufacturer instructions. After each attempt bacterial populations were reduced at many locations, but the population persisted within the facility. After several failed attempts at controlling the Salmonella population within this facility, it was decided that a gas-phase space decontamination was the most advantageous route to a successful decontamination of the C. Mahlon Kline intensive care and neonatal care building.
Current Decontamination Methods
Current decontamination methods for rooms and buildings include manual spray and wipe or soaking techniques using liquid disinfecting solutions; formaldehyde gas; hydrogen peroxide vapor; and chlorine dioxide gas. Manual spray and wiping and formaldehyde gassing are by far the primary methods and each has significant drawbacks.
Manual spray and wiping methods are the least effective methods of decontamination. It is subject to missed areas because of human error. The personnel performing the decontamination must spray each and every surface with the decontaminating agent, allow the agent to remain on the surface for the specified amount of time without drying (typically 10-20 minutes), then wipe the surface. This is particularly difficult in hard to reach areas such as corners, the under side of HVAC grills, floor drains, beneath components, etc.
Sprayers, foggers, and misters are an improvement of the manual spray and wipe technique since you have removed the person from the process, but they are limited in their ability or coverage. These methods create small size droplets that are heavier than air and settle downwards when sprayed or injected. While they get coverage on the walls, they do not get coverage on the underside of components. Additionally, spraying in odd shaped rooms, as in the Widener building does not get complete or even coverage. Formaldehyde is a very effective method that has been used longer than all of the other “gassing” methods and is well characterized. It is effective against a broad range of organisms, is low cost, and can effectively reach all surfaces. The major concern with decontaminating rooms, buildings, and vessels with formaldehyde is that it is listed as a potential carcinogen by the EPA (U.S. Department of Health and Human Services Public Health Services, National Toxicology Program, 2002). As of June 2004, the International Agency for Research on Cancer classified formaldehyde as carcinogenic to humans (IARC, 2004). Furthermore formaldehyde requires additional steps: neutralization and manual wiping of the neutralization byproduct. A residue is commonly left after such treatment, consisting of polymerized formaldehyde (paraformaldehyde) and the neutralization product (methenamine). The removal of such a residue was considered challenging for this facility. There was additional concern that residual formaldehyde from off-gassing would also be problematic both because of its odor and its perceived toxicity. This required step increases the amount of time involved, amount of personnel involved, and the cost in labor and time. Furthermore, formaldehyde concentrations are not monitored during the process thereby not assuring complete coverage throughout the facility.
Vapor hydrogen peroxide is somewhat effective under ideal conditions but falls short in real-life applications where there are even slight temperature gradients or an assortment of materials which affect the process. It is effective against a broad range of organisms, but celluloid materials such as flooring, boxes, ceiling tiles, paperwork, etc. absorb the peroxide thereby scavenging it from other areas [JSPPTOH, 4/04]. Under standard conditions, vapor hydrogen peroxide is a vapor, not a gas, which upon delivery to the room tends to transform back to its equilibrium state (liquid). Any cool surfaces or temperature gradients cause this to occur as condensation. This condensation on cooler surfaces caused by temperature gradients creates an uneven distribution of the decontaminating vapor. This creates areas with a greater amount of the decontaminating agent and areas with less or little, thereby not getting good distribution or more importantly good kill. Additionally vapor hydrogen peroxide has challenges in reaching difficult areas such as floor drains, HVAC grills, beneath furniture and components, the inside of cabinets, hinges, instruments and components. Vapor hydrogen peroxide was believed too problematic for the current application, particularly when interstitial spaces, ductwork and offices containing a lot of paper and celluloid materials were to be included within the decontamination.
Chlorine Dioxide
Chlorine dioxide (CD) is a greenish-yellow gas and is a single-electron-transfer oxidizing agent with a chlorine-like odor. Pure CD is an unstable gas and therefore is generated as needed. Although CD has "chlorine" in its name, its chemistry is radically different from that of chlorine. CD oxygenates products rather than chlorinating them and thus trihalomethane (THM’s) formation does not occur (Long, B.W.). Therefore, unlike chlorine, CD does not produce environmentally undesirable organic compounds containing chlorine.