- Email: [email protected]
Controlling bacterial contamination of dental impression guns
RESEARCH
Controlling bacterial contamination of dental impression guns Eric J. Westergard, BS; Laura M. Romito, DDS, MS; Michael J. Kowolik, BDS, FDS, PhD; Charles John Palenik, MS, PhD, MBA
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® Background. Dental impression material handgun cartridge dispensers are contaminated easily during clinical use. The authors A attempted to quantify contamination by bac3 RT I C LE teria, including methicillin-resistant Staphylococcus aureus (MRSA), of impression guns used in an academic dental clinic after five infection-prevention protocols were followed. Methods. The authors obtained samples from four commercially available impression guns at four specific sites (button, handle, latch, trigger) after routine clinical use, disinfection, steam sterilization (also known as autoclaving), steam sterilization followed by use of plastic impression gun covers and steam sterilization followed by use of plastic impression gun covers and disinfection. Results. The authors found that after routine clinical use, bacteria—including MRSA—heavily contaminated the impression guns. After the impression guns underwent disinfection, there was a 6 percent decrease in bacterial counts. The use of steam sterilization achieved sterility without harming the impression guns. Use of steam-sterilized impression guns with plastic impression gun covers decreased bacterial isolates by approximately 60 percent. Use of steam-sterilized impression guns plus covers and disinfection resulted in an approximately 95 percent reduction in contamination. Conclusions. The use of common infection-prevention methods appears to reduce the bacterial counts, including those of MRSA. Bacterial contamination was lowest after steam sterilization, followed by the use of plastic impression gun covers and disinfection. Clinical Implications. Use of contaminated impression guns on successive patients could increase the risk of causing crosstransmission of disease. The use of sterilization, plus plastic impression gun covers and disinfection, for impression guns after each use could be an effective and practical infection-control method for dental practices. Key Words. Infection prevention; disinfection; sterilization. JADA 2011;142(11):1269-1274. T
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ealth care–associated infections are a major cause of patient morbidity and mortality in the United States.1-3 Although the primary source of pathogens involved is the patient’s endogenous flora, an estimated 20 to 40 percent of health care–associated infections involve microorganisms being introduced to patients from the hands of health care workers.4 Contamination of hands can be the result of direct contact with patients or indirect contact with contaminated environmental surfaces. It also is possible that a patient could acquire an infection directly from a contaminated surface. The authors of studies from many countries have reported a lack of compliance with established disinfection guidelines,5-10 and compliance failures have been linked directly to outbreaks of disease.5-11 A number of factors can facilitate environmental surface-mediated transmission of pathogenic microorganisms.4,12,13 They include the ability of pathogens to survive and remain virulent environmentally for extended periods; the fact that environmental contamination is common; the ability of pathogens to colonize in patients; the ability of pathogens to colonize on the hands of health care workers, usually transiently; the fact that infection may result from small inoculating doses; and the fact that some pathogens are resistant to environmental sur-
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Mr. Westergard is a predoctoral student, Indiana University School of Dentistry, Indianapolis. Dr. Romito is an associate professor, Department of Oral Biology, and a faculty member, Comprehensive Care Clinic, Indiana University School of Dentistry, Indianapolis. Address reprint requests to Dr. Romito at Department of Oral Biology, Room B19C, Indiana University School of Dentistry, 1121 W. Michigan St., Indianapolis, Ind. 46202, e-mail “[email protected]”. Dr. Kowolik is a professor, Department of Periodontics and Allied Dental Programs, Indiana University School of Dentistry, Indianapolis. Dr. Palenik is the director, Infection Control Research and Services, Department of Oral Biology, Indiana University School of Dentistry, Indianapolis.
JADA 142(11)
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Copyright © 2011 American Dental Association. All rights reserved.
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face disinfectants. Surface contamination can be reduced by proper hand hygiene, as well as cleaning and disinfection.1,14 The latter is accomplished as a two-step process in which cleaning precedes disinfection. For example, an operatory countertop can be sprayed with a disinfectant solution and then wiped with a paper towel. Then, it is sprayed again and allowed to dry. This “spraywipe-spray” technique enhances decontamination through mechanical cleansing with the paper towel, which removes microorganisms present on the counter’s surface. The chemical action of the disinfectant solution further reduces surface contamination. The same process also occurs when using disinfectant wipes in a “wipe-discard-wipe” technique. The first disinfection wipe cleans by removing both microbes and adherent material, and the second wipe provides disinfection. Environmental contamination of surfaces with methicillin-resistant Staphylococcus aureus (MRSA) and the likelihood of MRSA infections can be reduced by taking appropriate infection-prevention measures.15-17 In 1968, Spaulding18 proposed a classification system for categorizing patient care items (for example, dental instruments, devices and equipment) depending on the potential risk of spreading infection associated with their intended use. Categories include critical, semicritical and noncritical items. Because critical items penetrate soft tissue or bone, they have the greatest risk of transmitting infection and should undergo heat sterilization before being used with another patient. Semicritical items (for example, amalgam condenser, reusable dental impression trays) touch mucous membranes or nonintact skin and have a lower risk of transmitting infection than do critical items. Because most semicritical items used in dentistry are heat tolerant, they also should be heat sterilized. If a semicritical item is heat sensitive, it should undergo high-level disinfection. Noncritical items contact intact skin, but not mucous membranes (for example, blood pressure cuff, face-bow, pulse oximeter). Such items can be decontaminated or barrier protected where they are used, as opposed to being transported to a central processing area.3,13,19 An item commonly used in dental offices and clinics that does not fit neatly into the Spaulding classification system is the dental impression material handgun cartridge dispenser, also known as an impression gun. Impression gun tips, which can contact nonintact skin and mucous membranes, are considered semicritical items. These tips are single1270
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use, disposable items. Typically, other areas of the impression gun do not come in contact with the patient and therefore could be considered noncritical. During use, however, they are handled repeatedly by health care workers’ gloved hands, which enter patients’ mouths and, therefore, can become contaminated easily. Thus, cleaning and disinfecting impression guns is critical, but it is difficult to do because the guns have many grooves, crevices and parts. Therefore, the use of gun covers or barrier devices may help reduce contamination. Use of barriers is supported by the Centers for Disease Control and Prevention’s dental infection-control guidelines, which state that “cleaning or disinfection of certain noncritical patient-care items can be difficult or damage the surfaces; therefore, use of disposable barrier protection of these surfaces might be a preferred alternative.”3 There is a dearth of information concerning transmission of infectious agents to patients via noncritical items. These types of items, however, may be involved in secondary transmission by means of contaminating practitioners’ hands or coming into contact with materials and equipment that subsequently may be used in patients.19,20 We conducted a study to evaluate the presence of bacteria, including MRSA, on dental impression material handgun cartridge dispensers used in an academic dental clinic. We also assessed the effectiveness of several infection-prevention methods on reducing contamination levels on impression guns. We hypothesized that there would be significant bacterial contamination of dental impression guns after routine clinical use and after use of infection-prevention procedures, and that the use of a plastic impression gun cover would reduce surface contamination. METHODS
Impression guns. We conducted experiments involving four dental impression material handgun cartridge dispensers (Garant 2 4:1/10:1 dispenser, 3M ESPE, St. Paul, Minn.) in the predoctoral Comprehensive Care Clinic at the Indiana University School of Dentistry (IUSD), Indianapolis. In the clinic, individual impression guns were used approximately 10 times per week. The routine practice was for ABBREVIATION KEY. CFU/mL: Colony-forming units per milliliter. ETSA: Enriched trypticase soy agar. IUSD: Indiana University School of Dentistry. MRSA: Methicillin-resistant Staphylococcus aureus. MSA: Mannitol salt agar. PBS: Phosphate-buffered saline.
November 2011
Copyright © 2011 American Dental Association. All rights reserved.
RESEARCH
dental students to obtain an impression gun from the clinical dispensing area and return it to a clinical dental assistant after use. IUSD does not have an official policy concerning impression gun environmental asepsis except for a general recommendation that clinical dental assistants disinfect the impression guns after each use by employing the spray-wipespray technique with concentrated commercial surface disinfectants. Sampling. We designated four sites on each impression gun as sampling areas: the trigger, the handle, the release button and the latch, which holds the impression cartridges in place. We sampled the sites by moistening two sterile cotton swabs with sterile phosphate-buffered saline (PBS) (0.85 molars; pH = 7.2) and moving the swabs in a steady side-to-side sweeping motion with some rotation for 20 seconds over the entire surface of the sampled site. We placed the two cotton swabs used for each site into a tube containing 2.0 milliliters of PBS and transported the tube to a laboratory immediately. Specimen culturing. Our goal in culturing specimens was to determine the total number of bacterial colonies, including S. aureus species and MRSA, growing on each surface. Initially, the specimens underwent spiral plating onto two enriched trypticase soy agar (ETSA) plates and a mannitol salt agar (MSA) plate, and we incubated them at 37˚C for 48 hours. One ETSA plate and the MSA plate were incubated aerobically, and the second ETSA plate was incubated anaerobically. ETSA supports the growth of many bacteria. Growth on MSA plates usually indicates the presence of Staphylococcus species. We determined the number of colonies and then divided the colonies into groups with shared visual characteristics. Colony types that had the physical appearance of Staphylococcus species underwent subculturing in trypticase soy broth with 0.25 percent (grams of solute per 100 mL of solution) glucose. We aerobically incubated these samples at 37˚C for 48 hours. We spread 0.1 mL of the subcultured organisms on plates containing three types of media: MSA and two highly selective and differentiating media designed for the growth and identification of MRSA. We aerobically incubated these samples at 37˚C for 48 hours. Experiment I: routine use. The first experiment served as a control. The four impression guns were in routine use in IUSD’s Comprehensive Care Clinic for three weeks before we began collecting samples. We removed all other impression guns from the clinic to ensure that only the four new study impression guns would be
used to dispense dental elastomeric impression material during the experimental period. During these three weeks, staff members and students followed the standard infectionprevention protocol for the study impression guns. They obtained the impression guns from a clean dispensing area, and they returned the impression guns to a clinical dental assistant to be cleaned and disinfected with a concentrated commercial surface disinfectant using the spray-wipespray technique after being used with a patient. We obtained specimens from the four designated sampling areas on each gun and conducted sampling and culturing as described previously. Experiment II: disinfection. We steam sterilized the four impression guns before the start of experiment II. We returned the impression guns to the clinic, and students and staff members used them for three weeks. During this time, the clinical dental assistant followed the previously mentioned routine cleaning and disinfection protocols after the impression guns were used on individual patients. Subsequently, we removed the impression guns from the clinic and disinfected the entirety of each gun using the wipe-discard-wipe technique. We then obtained samples and cultured them as described previously. Experiment III: steam sterilization. After we obtained samples from the impression guns at the end of experiment II, we steam sterilized the four impression guns in one of IUSD’s largevolume, high-vacuum steam sterilizer units. Such units commonly are present in central sterilization departments in hospitals or large clinics. The operating conditions were 214 kilopascals at 131˚C for 10 minutes, with prevacuum and postvacuum cycles of seven minutes each. After processing, we obtained samples from the impression guns and cultured the samples as described previously. Experiment IV: steam sterilization followed by the use of impression gun covers. Immediately after we concluded experiment III, we steam sterilized the impression guns again and returned them to the clinic to be used for three weeks. For this experimental protocol, the only infection-prevention methods staff members and students used were plastic impression gun covers (Metrex Total Care, Orange, Calif.). The plastic impression gun covers (Figure) are single-use, disposable items. Because the use of impression gun covers was new to the IUSD clinic, we met with the clinic staff members and students to inform them of the availability of the gun covers and the protocol for using them. We instructed students and staff members to JADA 142(11)
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percent) disinfection. MRSA was present before (2.7 percent of isolates) and after (4.0 percent) disinfection. All of the sampling sites had at least one MRSA isolate. The results from the use of the two highly selective and differentiating media designed for the growth and identification of MRSA were similar. When we obtained samples from the impression guns and cultured the samples immediately after steam sterilization, there were no bacterial isolates. Moreover, processing the impression Figure. Impression gun with plastic cover. Image of 3M ESPE Garant 2 4:1/10:1 impression guns through a highmaterial dispenser reproduced with permission of 3M, St. Paul, Minn. Image of Pinnacle plastic vacuum steam sterilizer impression gun cover reproduced with permission of Metrex Total Care, Orange, Calif. did not affect their slip the covers over the guns in a fluid motion integrity or functionality. Compared with disinwhile minimally handling both items with fection, steam sterilization followed by the use washed, ungloved hands. We posted alongside of plastic gun covers for three weeks reduced the impression guns and gun covers in the bacterial contamination by approximately 60 clinic’s dispensing area written instruction with percent. Steam sterilization followed by the use graphics for how to use the covers. At the end of of plastic gun covers plus disinfection after each three weeks, we obtained samples from the use reduced bacterial contamination by approxiimpression guns and cultured the samples as mately 95 percent compared with disinfection. described previously. The use of the clinical protocol in experiment V Experiment V: steam sterilization folresulted in no MRSA isolates. lowed by the use of impression gun covers Table 2 identifies MRSA isolates according to and disinfection. After steam sterilizing the the sampling site for all five experiments. Disimpression guns, we returned them to the clinic tribution of MRSA, when it was present, was to be used for three weeks. During this time, gun relatively even among the four sites. No site had covers were used as described previously, and the noticeably higher numbers of MRSA than did clinical dental assistants were instructed to clean the others. and disinfect the guns in their usual manner DISCUSSION after each use. We obtained samples from the impression guns and cultured the samples as Similar to other dental equipment items used in described previously. patient care, dental impression material handgun cartridge dispensers easily become contamiRESULTS nated microbially. If they are not covered or Table 1 presents the bacterial isolate results. treated to reduce contamination, impression After three weeks of routine clinical use and guns could be sources of cross-contamination. infection-prevention measures, sampling and The results of our study support this assertion. cultivation from the four dental impression There are no survey data available that indiguns produced 184 bacterial isolates for all four cate the usage patterns of plastic impression gun impression guns. Three weeks of routine clinical covers or the frequency of steam sterilizing use and infection-prevention measures followed impression guns among U.S. dental practices. by disinfection did little to reduce bacterial conAlthough some or even many dental practitioners tamination. All of the sampling sites had similar may have office protocols requiring disinfection levels of contamination. S. aureus was present of impression guns between uses, the proportion before (9.1 percent of isolates) and after (16.2 who does so is not known. The Centers for Dis1272 JADA 142(11)
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Copyright © 2011 American Dental Association. All rights reserved.
RESEARCH TABLE 1
Bacterial isolates from all impression guns.* ISOLATES
EXPERIMENT I: ROUTINE CLINICAL USE (CFU/mL†)
EXPERIMENT II: DISINFECTION (CFU/mL)
EXPERIMENT III: STEAM STERILIZATION (CFU/mL)
EXPERIMENT IV: STEAM STERILIZATION AND IMPRESSION GUN COVERS (CFU/mL)
EXPERIMENT V: STEAM STERILIZATION, IMPRESSION GUN COVERS AND DISINFECTION (CFU/mL)
184
173
0
75
9
Staphylococcus aureus
17
28
0
11
2
MethicillinResistant Staphylococcus aureus‡
5
7
0
4
0
All
* Results are the combined numbers from four impression guns. † CFU/mL: Colony-forming units per milliliter. ‡ Based on the results from the highly selective and differentiating media designed for the growth and identification of methicillin-resistant Staphylococcus aureus.
TABLE 2
Methicillin-resistant Staphylococcus aureus isolates from all impression guns, according to sampling site.* SAMPLING SITE
EXPERIMENT I: ROUTINE CLINICAL USE (CFU/mL†)
EXPERIMENT II: DISINFECTION (CFU/mL)
EXPERIMENT III: STEAM STERILIZATION (CFU/mL)
EXPERIMENT: IV STEAM STERILIZATION AND IMPRESSION GUN COVERS (CFU/mL)
EXPERIMENT V: STEAM STERILIZATION, IMPRESSION GUN COVERS AND DISINFECTION (CFU/mL)
Button
2
3
0
1
0
Handle
1
2
0
1
0
Latch
1
1
0
0
0
Trigger
1
1
0
2
0
* Based on the results from the highly selective and differentiating media designed for the growth and identification of methicillin-resistant Staphylococcus aureus. † CFU/mL: Colony-forming units per milliliter.
ease Control and Prevention’s guidelines offer no infection-prevention recommendations specifically for dental impression guns, but they do state, “Heat-tolerant items ... used in the mouth should be heat-sterilized before being used on another patient. Items that do not normally contact the patient, prosthetic device, or appliance but frequently become contaminated and cannot withstand heat-sterilization ... should be cleaned and disinfected between patients and according to the manufacturer’s instructions.”3 Although the manufacturer of the impression guns we used in our study indicated that they are suitable for steam sterilization,21 dental product sales representatives, purchasing dentists or both may not be aware of this information. Manufacturers may not always provide such information in the product packaging or sales brochures; nevertheless, it is incumbent on dental team members to read the products’ technical information so that
they handle items appropriately and maintain optimal patient safety. The results of research studies have shown that MRSA can survive in the environment for a minimum of a few days and up to several weeks under optimal conditions, thus providing an opportunity for cross-transmission.4,12,22,23 A single disinfection procedure appears incapable of markedly reducing bacterial contamination on impression guns after clinical use. However, we successfully decontaminated unclean guns after three weeks of clinical use by means of steam sterilization. After steam sterilization, there were no bacteria on and no evident damage to the impression guns. Even after steam sterilizing the impression guns, the use of impression gun covers reduced total contamination by only about 60 percent compared with disinfection and did not eliminate MRSA. However, steam sterilization, plus JADA 142(11)
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the combined use of impression gun covers and disinfection after each use, resulted in few bacterial colonies on impression guns that initially were sterile. Steam sterilization and disinfection are processes used routinely in dental practices. By pairing these processes with the use of plastic impression gun covers, dental practitioners may be able to address the potential for impression guns to contribute to the transfer of disease. Moreover, impression gun covers, such as those used in this study, can be incorporated into dental practices for a relatively low cost. The results of our study are preliminary. Our evaluation involved only one type of impression gun, surface disinfectant, steam sterilization and plastic impression gun cover. The test group included only four impression guns, and each experimental period was three weeks. In addition, we did not observe directly the compliance of clinical staff members and students with study procedures and protocols. Although the dental impression material handgun cartridge dispensers used during our study had no visible or functional damage from steam sterilization, additional studies are needed to better determine the long-term effect of steam sterilization on other types of impression guns in terms of function and durability. CONCLUSIONS
In our study, bacterial contamination, including MSRA contamination, occurred easily during routine clinical use of dental impression material handgun cartridge dispensers. Steam sterilization successfully sterilized contaminated impression guns. If our findings are supported by the results of additional research, the use of sterilization of impression guns after each use, plastic gun covers with each patient and disinfection after each use could be an effective and practical infection-prevention method for dental practices. ■ Disclosure. None of the authors reported any disclosures. This project received funding from the Indiana University School of Dentistry (IUSD) Infection Control Research Services, and the IUSD Student Research Program, Indianapolis. Patterson Dental, St. Paul, Minn., contributed the impression guns used in the study. The authors thank the staff members and students of Indiana University School of Dentistry Comprehensive Care Clinic A, Indianapolis, for their assistance and cooperation. 1. Rutala WA, Weber DJ; Centers for Disease Control and Prevention (CDC) Healthcare Infection Control Practices Advisory Committee (HICPAC). Guideline for disinfection and sterilization in healthcare facilities, 2008. “www.cdc.gov/ncidod/dhqp/pdf/guidelines/ disinfection_nov_2008.pdf”. Accessed Sept. 6, 2011. 2. Sehulster L, Chinn RY; Centers for Disease Control and Prevention (CDC); Healthcare Infection Control Practices Advisory Committee (HICPAC). Guidelines for environmental infection control in
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health-care facilities: recommendations of CDC and the Healthcare Infection Control Practices Advisory Committee (HICPAC). MMWR Recomm Rep 2003;52(RR-10):1-42. 3. Kohn WG, Collins AS, Cleveland JL, Harte JA, Eklund KJ, Malvitz DM; Centers for Disease Control and Prevention (CDC). Guidelines for infection control in dental health-care settings: 2003. MMWR Recomm Rep 2003;52(RR-17):1-61. 4. Weber DJ, Rutala WA, Miller MB, Huslage K, Sickbert-Bennett E. Role of hospital surfaces in the transmission of emerging health care-associated pathogens: norovirus, Clostridium difficile, and Acinetobacter species. Am J Infect Control 2010;38(5 suppl 1):S25-S33. 5. McCarthy GM, Koval JJ, John MA, MacDonald JK. Infection control practices across Canada: do dentists follow the recommendations? J Can Dent Assoc 1999;65(9):506-511. 6. Spach DH, Silverstein FE, Stamm WE. Transmission of infection by gastrointestinal endoscopy and bronchoscopy. Ann Intern Med 1993;118(2):117-128. 7. Weber DJ, Rutala WA. Lessons from outbreaks associated with bronchoscopy. Infect Control Hosp Epidemiol 2001;22(7):403-408. 8. Weber DJ, Rutala WA, DiMarino AJ Jr. The prevention of infection following gastrointestinal endoscopy: the importance of prophylaxis and reprocessing. In: DiMarino AJ Jr, Benjamin SB, eds. Gastrointestinal diseases: an endoscopic approach. Thorofare, N.J.: Slack; 2002:87-106. 9. Meyers H, Brown-Elliott BA, Moore D, et al. An outbreak of Mycobacterium chelonae infection following liposuction. Clin Infect Dis 2002;34(11):1500-1507. 10. Lowry PW, Jarvis WR, Oberle AD, et al. Mycobacterium chelonae causing otitis media in an ear-nose-and-throat practice. N Engl J Med 1988;319(15):978-982. 11. Weber DJ, Rutala WA. Lessons from outbreaks associated with bronchoscopy. Infect Control Hosp Epidemiol 2001;22(7):403-408. 12. Boyce J. Environmental contamination makes an important contribution to hospital infection. J Hosp Infect 2007;65(suppl 2):50-54. 13. Miller CH, Palenik CJ. Infection Control and Management of Hazardous Materials for the Dental Team. 4th ed. St. Louis: Mosby; 2010:25-36. 14. Boyce JM, Pittet D; Healthcare Infection Control Practices Advisory Committee (HICPAC); HICPAC/SHEA/APIC/IDSA Hand Hygiene Task Force. Guideline for hand hygiene in health-care settings: recommendations of the Healthcare Infection Control Practices Advisory Committee and the HICPAC/SHEA/APIC/IDSA Hand Hygiene Task Force. Society for Healthcare Epidemiology of America/Association for Professionals in Infection Control/Infectious Diseases Society of America. MMWR Recomm Rep 2002;51(RR-16):1-45. 15. Goodman ER, Platt R, Bass R, Onderdonk AB, Yokoe DS, Huang SS. Impact of an environmental cleaning intervention on the presence of methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci on surfaces in intensive care unit rooms. Infect Control Hosp Epidemiol 2008;29(7):593-599. 16. Dancer SJ, Lamb J, Girvan EK, Robertson C. Measuring the effect of enhanced cleaning in a UK hospital: a prospective cross-over study. BMC Med 2009;7:28. 17. Ghaznavi-Rad E, Ghasemzadeh-Moghaddam H, Shamsudin MN, et al. Environmental contamination in the hospital as a possible source for nosocomial infection with methicillin-resistant Staphylococcus aureus (published online ahead of print Oct. 28, 2010). Infect Control Hosp Epidemiol 2010;31(12):1302-1303. doi:10.1086/657587. 18. Spaulding EH. Chemical disinfection of medical and surgical material. In: Lawrence CA, Block SS, Reddish GF, eds. Disinfection, Sterilization, and Preservation. Philadelphia: Lea & Febiger; 1968: 517-531. 19. Rutala WA, Weber DJ. Disinfection and sterilization in health care facilities: what clinicians need to know (published online ahead of print Aug. 12, 2004). Clin Infect Dis 2004;39(5):702-709. doi:10. 1086/423182. 20. Weber DJ, Rutala WA. Environmental issues and nosocomial infections. In: Enzel RP, ed. Prevention and Control of Nosocomial Infections. Baltimore: Williams & Wilkins; 1997:491-514. 21. 3M ESPE. ImprintTM II GarantTM Quick Step Heavy Body/Light Body Impression Material System Technical Product Profile. St. Paul, Minn.: 3M ESPE Dental Products; 2002:18. 22. Beard-Pegler MA, Stubbs E, Vickery AM. Observations on the resistance to drying of staphylococcal strains. J Med Microbiol 1988; 26(4):251-255. 23. Duckworth GJ, Jordens JZ. Adherence and survival properties of an epidemic methicillin-resistant strain of Staphylococcus aureus compared with those of methicillin-sensitive strains. J Med Microbiol 1990;32(3):195-200.
November 2011
Copyright © 2011 American Dental Association. All rights reserved.
Controlling bacterial contamination of dental impression guns Eric J. Westergard, BS; Laura M. Romito, DDS, MS; Michael J. Kowolik, BDS, FDS, PhD; Charles John Palenik, MS, PhD, MBA
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® Background. Dental impression material handgun cartridge dispensers are contaminated easily during clinical use. The authors A attempted to quantify contamination by bac3 RT I C LE teria, including methicillin-resistant Staphylococcus aureus (MRSA), of impression guns used in an academic dental clinic after five infection-prevention protocols were followed. Methods. The authors obtained samples from four commercially available impression guns at four specific sites (button, handle, latch, trigger) after routine clinical use, disinfection, steam sterilization (also known as autoclaving), steam sterilization followed by use of plastic impression gun covers and steam sterilization followed by use of plastic impression gun covers and disinfection. Results. The authors found that after routine clinical use, bacteria—including MRSA—heavily contaminated the impression guns. After the impression guns underwent disinfection, there was a 6 percent decrease in bacterial counts. The use of steam sterilization achieved sterility without harming the impression guns. Use of steam-sterilized impression guns with plastic impression gun covers decreased bacterial isolates by approximately 60 percent. Use of steam-sterilized impression guns plus covers and disinfection resulted in an approximately 95 percent reduction in contamination. Conclusions. The use of common infection-prevention methods appears to reduce the bacterial counts, including those of MRSA. Bacterial contamination was lowest after steam sterilization, followed by the use of plastic impression gun covers and disinfection. Clinical Implications. Use of contaminated impression guns on successive patients could increase the risk of causing crosstransmission of disease. The use of sterilization, plus plastic impression gun covers and disinfection, for impression guns after each use could be an effective and practical infection-control method for dental practices. Key Words. Infection prevention; disinfection; sterilization. JADA 2011;142(11):1269-1274. T
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CON
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ealth care–associated infections are a major cause of patient morbidity and mortality in the United States.1-3 Although the primary source of pathogens involved is the patient’s endogenous flora, an estimated 20 to 40 percent of health care–associated infections involve microorganisms being introduced to patients from the hands of health care workers.4 Contamination of hands can be the result of direct contact with patients or indirect contact with contaminated environmental surfaces. It also is possible that a patient could acquire an infection directly from a contaminated surface. The authors of studies from many countries have reported a lack of compliance with established disinfection guidelines,5-10 and compliance failures have been linked directly to outbreaks of disease.5-11 A number of factors can facilitate environmental surface-mediated transmission of pathogenic microorganisms.4,12,13 They include the ability of pathogens to survive and remain virulent environmentally for extended periods; the fact that environmental contamination is common; the ability of pathogens to colonize in patients; the ability of pathogens to colonize on the hands of health care workers, usually transiently; the fact that infection may result from small inoculating doses; and the fact that some pathogens are resistant to environmental sur-
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Mr. Westergard is a predoctoral student, Indiana University School of Dentistry, Indianapolis. Dr. Romito is an associate professor, Department of Oral Biology, and a faculty member, Comprehensive Care Clinic, Indiana University School of Dentistry, Indianapolis. Address reprint requests to Dr. Romito at Department of Oral Biology, Room B19C, Indiana University School of Dentistry, 1121 W. Michigan St., Indianapolis, Ind. 46202, e-mail “[email protected]”. Dr. Kowolik is a professor, Department of Periodontics and Allied Dental Programs, Indiana University School of Dentistry, Indianapolis. Dr. Palenik is the director, Infection Control Research and Services, Department of Oral Biology, Indiana University School of Dentistry, Indianapolis.
JADA 142(11)
http://jada.ada.org
Copyright © 2011 American Dental Association. All rights reserved.
November 2011
1269
RESEARCH
face disinfectants. Surface contamination can be reduced by proper hand hygiene, as well as cleaning and disinfection.1,14 The latter is accomplished as a two-step process in which cleaning precedes disinfection. For example, an operatory countertop can be sprayed with a disinfectant solution and then wiped with a paper towel. Then, it is sprayed again and allowed to dry. This “spraywipe-spray” technique enhances decontamination through mechanical cleansing with the paper towel, which removes microorganisms present on the counter’s surface. The chemical action of the disinfectant solution further reduces surface contamination. The same process also occurs when using disinfectant wipes in a “wipe-discard-wipe” technique. The first disinfection wipe cleans by removing both microbes and adherent material, and the second wipe provides disinfection. Environmental contamination of surfaces with methicillin-resistant Staphylococcus aureus (MRSA) and the likelihood of MRSA infections can be reduced by taking appropriate infection-prevention measures.15-17 In 1968, Spaulding18 proposed a classification system for categorizing patient care items (for example, dental instruments, devices and equipment) depending on the potential risk of spreading infection associated with their intended use. Categories include critical, semicritical and noncritical items. Because critical items penetrate soft tissue or bone, they have the greatest risk of transmitting infection and should undergo heat sterilization before being used with another patient. Semicritical items (for example, amalgam condenser, reusable dental impression trays) touch mucous membranes or nonintact skin and have a lower risk of transmitting infection than do critical items. Because most semicritical items used in dentistry are heat tolerant, they also should be heat sterilized. If a semicritical item is heat sensitive, it should undergo high-level disinfection. Noncritical items contact intact skin, but not mucous membranes (for example, blood pressure cuff, face-bow, pulse oximeter). Such items can be decontaminated or barrier protected where they are used, as opposed to being transported to a central processing area.3,13,19 An item commonly used in dental offices and clinics that does not fit neatly into the Spaulding classification system is the dental impression material handgun cartridge dispenser, also known as an impression gun. Impression gun tips, which can contact nonintact skin and mucous membranes, are considered semicritical items. These tips are single1270
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use, disposable items. Typically, other areas of the impression gun do not come in contact with the patient and therefore could be considered noncritical. During use, however, they are handled repeatedly by health care workers’ gloved hands, which enter patients’ mouths and, therefore, can become contaminated easily. Thus, cleaning and disinfecting impression guns is critical, but it is difficult to do because the guns have many grooves, crevices and parts. Therefore, the use of gun covers or barrier devices may help reduce contamination. Use of barriers is supported by the Centers for Disease Control and Prevention’s dental infection-control guidelines, which state that “cleaning or disinfection of certain noncritical patient-care items can be difficult or damage the surfaces; therefore, use of disposable barrier protection of these surfaces might be a preferred alternative.”3 There is a dearth of information concerning transmission of infectious agents to patients via noncritical items. These types of items, however, may be involved in secondary transmission by means of contaminating practitioners’ hands or coming into contact with materials and equipment that subsequently may be used in patients.19,20 We conducted a study to evaluate the presence of bacteria, including MRSA, on dental impression material handgun cartridge dispensers used in an academic dental clinic. We also assessed the effectiveness of several infection-prevention methods on reducing contamination levels on impression guns. We hypothesized that there would be significant bacterial contamination of dental impression guns after routine clinical use and after use of infection-prevention procedures, and that the use of a plastic impression gun cover would reduce surface contamination. METHODS
Impression guns. We conducted experiments involving four dental impression material handgun cartridge dispensers (Garant 2 4:1/10:1 dispenser, 3M ESPE, St. Paul, Minn.) in the predoctoral Comprehensive Care Clinic at the Indiana University School of Dentistry (IUSD), Indianapolis. In the clinic, individual impression guns were used approximately 10 times per week. The routine practice was for ABBREVIATION KEY. CFU/mL: Colony-forming units per milliliter. ETSA: Enriched trypticase soy agar. IUSD: Indiana University School of Dentistry. MRSA: Methicillin-resistant Staphylococcus aureus. MSA: Mannitol salt agar. PBS: Phosphate-buffered saline.
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RESEARCH
dental students to obtain an impression gun from the clinical dispensing area and return it to a clinical dental assistant after use. IUSD does not have an official policy concerning impression gun environmental asepsis except for a general recommendation that clinical dental assistants disinfect the impression guns after each use by employing the spray-wipespray technique with concentrated commercial surface disinfectants. Sampling. We designated four sites on each impression gun as sampling areas: the trigger, the handle, the release button and the latch, which holds the impression cartridges in place. We sampled the sites by moistening two sterile cotton swabs with sterile phosphate-buffered saline (PBS) (0.85 molars; pH = 7.2) and moving the swabs in a steady side-to-side sweeping motion with some rotation for 20 seconds over the entire surface of the sampled site. We placed the two cotton swabs used for each site into a tube containing 2.0 milliliters of PBS and transported the tube to a laboratory immediately. Specimen culturing. Our goal in culturing specimens was to determine the total number of bacterial colonies, including S. aureus species and MRSA, growing on each surface. Initially, the specimens underwent spiral plating onto two enriched trypticase soy agar (ETSA) plates and a mannitol salt agar (MSA) plate, and we incubated them at 37˚C for 48 hours. One ETSA plate and the MSA plate were incubated aerobically, and the second ETSA plate was incubated anaerobically. ETSA supports the growth of many bacteria. Growth on MSA plates usually indicates the presence of Staphylococcus species. We determined the number of colonies and then divided the colonies into groups with shared visual characteristics. Colony types that had the physical appearance of Staphylococcus species underwent subculturing in trypticase soy broth with 0.25 percent (grams of solute per 100 mL of solution) glucose. We aerobically incubated these samples at 37˚C for 48 hours. We spread 0.1 mL of the subcultured organisms on plates containing three types of media: MSA and two highly selective and differentiating media designed for the growth and identification of MRSA. We aerobically incubated these samples at 37˚C for 48 hours. Experiment I: routine use. The first experiment served as a control. The four impression guns were in routine use in IUSD’s Comprehensive Care Clinic for three weeks before we began collecting samples. We removed all other impression guns from the clinic to ensure that only the four new study impression guns would be
used to dispense dental elastomeric impression material during the experimental period. During these three weeks, staff members and students followed the standard infectionprevention protocol for the study impression guns. They obtained the impression guns from a clean dispensing area, and they returned the impression guns to a clinical dental assistant to be cleaned and disinfected with a concentrated commercial surface disinfectant using the spray-wipespray technique after being used with a patient. We obtained specimens from the four designated sampling areas on each gun and conducted sampling and culturing as described previously. Experiment II: disinfection. We steam sterilized the four impression guns before the start of experiment II. We returned the impression guns to the clinic, and students and staff members used them for three weeks. During this time, the clinical dental assistant followed the previously mentioned routine cleaning and disinfection protocols after the impression guns were used on individual patients. Subsequently, we removed the impression guns from the clinic and disinfected the entirety of each gun using the wipe-discard-wipe technique. We then obtained samples and cultured them as described previously. Experiment III: steam sterilization. After we obtained samples from the impression guns at the end of experiment II, we steam sterilized the four impression guns in one of IUSD’s largevolume, high-vacuum steam sterilizer units. Such units commonly are present in central sterilization departments in hospitals or large clinics. The operating conditions were 214 kilopascals at 131˚C for 10 minutes, with prevacuum and postvacuum cycles of seven minutes each. After processing, we obtained samples from the impression guns and cultured the samples as described previously. Experiment IV: steam sterilization followed by the use of impression gun covers. Immediately after we concluded experiment III, we steam sterilized the impression guns again and returned them to the clinic to be used for three weeks. For this experimental protocol, the only infection-prevention methods staff members and students used were plastic impression gun covers (Metrex Total Care, Orange, Calif.). The plastic impression gun covers (Figure) are single-use, disposable items. Because the use of impression gun covers was new to the IUSD clinic, we met with the clinic staff members and students to inform them of the availability of the gun covers and the protocol for using them. We instructed students and staff members to JADA 142(11)
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percent) disinfection. MRSA was present before (2.7 percent of isolates) and after (4.0 percent) disinfection. All of the sampling sites had at least one MRSA isolate. The results from the use of the two highly selective and differentiating media designed for the growth and identification of MRSA were similar. When we obtained samples from the impression guns and cultured the samples immediately after steam sterilization, there were no bacterial isolates. Moreover, processing the impression Figure. Impression gun with plastic cover. Image of 3M ESPE Garant 2 4:1/10:1 impression guns through a highmaterial dispenser reproduced with permission of 3M, St. Paul, Minn. Image of Pinnacle plastic vacuum steam sterilizer impression gun cover reproduced with permission of Metrex Total Care, Orange, Calif. did not affect their slip the covers over the guns in a fluid motion integrity or functionality. Compared with disinwhile minimally handling both items with fection, steam sterilization followed by the use washed, ungloved hands. We posted alongside of plastic gun covers for three weeks reduced the impression guns and gun covers in the bacterial contamination by approximately 60 clinic’s dispensing area written instruction with percent. Steam sterilization followed by the use graphics for how to use the covers. At the end of of plastic gun covers plus disinfection after each three weeks, we obtained samples from the use reduced bacterial contamination by approxiimpression guns and cultured the samples as mately 95 percent compared with disinfection. described previously. The use of the clinical protocol in experiment V Experiment V: steam sterilization folresulted in no MRSA isolates. lowed by the use of impression gun covers Table 2 identifies MRSA isolates according to and disinfection. After steam sterilizing the the sampling site for all five experiments. Disimpression guns, we returned them to the clinic tribution of MRSA, when it was present, was to be used for three weeks. During this time, gun relatively even among the four sites. No site had covers were used as described previously, and the noticeably higher numbers of MRSA than did clinical dental assistants were instructed to clean the others. and disinfect the guns in their usual manner DISCUSSION after each use. We obtained samples from the impression guns and cultured the samples as Similar to other dental equipment items used in described previously. patient care, dental impression material handgun cartridge dispensers easily become contamiRESULTS nated microbially. If they are not covered or Table 1 presents the bacterial isolate results. treated to reduce contamination, impression After three weeks of routine clinical use and guns could be sources of cross-contamination. infection-prevention measures, sampling and The results of our study support this assertion. cultivation from the four dental impression There are no survey data available that indiguns produced 184 bacterial isolates for all four cate the usage patterns of plastic impression gun impression guns. Three weeks of routine clinical covers or the frequency of steam sterilizing use and infection-prevention measures followed impression guns among U.S. dental practices. by disinfection did little to reduce bacterial conAlthough some or even many dental practitioners tamination. All of the sampling sites had similar may have office protocols requiring disinfection levels of contamination. S. aureus was present of impression guns between uses, the proportion before (9.1 percent of isolates) and after (16.2 who does so is not known. The Centers for Dis1272 JADA 142(11)
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RESEARCH TABLE 1
Bacterial isolates from all impression guns.* ISOLATES
EXPERIMENT I: ROUTINE CLINICAL USE (CFU/mL†)
EXPERIMENT II: DISINFECTION (CFU/mL)
EXPERIMENT III: STEAM STERILIZATION (CFU/mL)
EXPERIMENT IV: STEAM STERILIZATION AND IMPRESSION GUN COVERS (CFU/mL)
EXPERIMENT V: STEAM STERILIZATION, IMPRESSION GUN COVERS AND DISINFECTION (CFU/mL)
184
173
0
75
9
Staphylococcus aureus
17
28
0
11
2
MethicillinResistant Staphylococcus aureus‡
5
7
0
4
0
All
* Results are the combined numbers from four impression guns. † CFU/mL: Colony-forming units per milliliter. ‡ Based on the results from the highly selective and differentiating media designed for the growth and identification of methicillin-resistant Staphylococcus aureus.
TABLE 2
Methicillin-resistant Staphylococcus aureus isolates from all impression guns, according to sampling site.* SAMPLING SITE
EXPERIMENT I: ROUTINE CLINICAL USE (CFU/mL†)
EXPERIMENT II: DISINFECTION (CFU/mL)
EXPERIMENT III: STEAM STERILIZATION (CFU/mL)
EXPERIMENT: IV STEAM STERILIZATION AND IMPRESSION GUN COVERS (CFU/mL)
EXPERIMENT V: STEAM STERILIZATION, IMPRESSION GUN COVERS AND DISINFECTION (CFU/mL)
Button
2
3
0
1
0
Handle
1
2
0
1
0
Latch
1
1
0
0
0
Trigger
1
1
0
2
0
* Based on the results from the highly selective and differentiating media designed for the growth and identification of methicillin-resistant Staphylococcus aureus. † CFU/mL: Colony-forming units per milliliter.
ease Control and Prevention’s guidelines offer no infection-prevention recommendations specifically for dental impression guns, but they do state, “Heat-tolerant items ... used in the mouth should be heat-sterilized before being used on another patient. Items that do not normally contact the patient, prosthetic device, or appliance but frequently become contaminated and cannot withstand heat-sterilization ... should be cleaned and disinfected between patients and according to the manufacturer’s instructions.”3 Although the manufacturer of the impression guns we used in our study indicated that they are suitable for steam sterilization,21 dental product sales representatives, purchasing dentists or both may not be aware of this information. Manufacturers may not always provide such information in the product packaging or sales brochures; nevertheless, it is incumbent on dental team members to read the products’ technical information so that
they handle items appropriately and maintain optimal patient safety. The results of research studies have shown that MRSA can survive in the environment for a minimum of a few days and up to several weeks under optimal conditions, thus providing an opportunity for cross-transmission.4,12,22,23 A single disinfection procedure appears incapable of markedly reducing bacterial contamination on impression guns after clinical use. However, we successfully decontaminated unclean guns after three weeks of clinical use by means of steam sterilization. After steam sterilization, there were no bacteria on and no evident damage to the impression guns. Even after steam sterilizing the impression guns, the use of impression gun covers reduced total contamination by only about 60 percent compared with disinfection and did not eliminate MRSA. However, steam sterilization, plus JADA 142(11)
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the combined use of impression gun covers and disinfection after each use, resulted in few bacterial colonies on impression guns that initially were sterile. Steam sterilization and disinfection are processes used routinely in dental practices. By pairing these processes with the use of plastic impression gun covers, dental practitioners may be able to address the potential for impression guns to contribute to the transfer of disease. Moreover, impression gun covers, such as those used in this study, can be incorporated into dental practices for a relatively low cost. The results of our study are preliminary. Our evaluation involved only one type of impression gun, surface disinfectant, steam sterilization and plastic impression gun cover. The test group included only four impression guns, and each experimental period was three weeks. In addition, we did not observe directly the compliance of clinical staff members and students with study procedures and protocols. Although the dental impression material handgun cartridge dispensers used during our study had no visible or functional damage from steam sterilization, additional studies are needed to better determine the long-term effect of steam sterilization on other types of impression guns in terms of function and durability. CONCLUSIONS
In our study, bacterial contamination, including MSRA contamination, occurred easily during routine clinical use of dental impression material handgun cartridge dispensers. Steam sterilization successfully sterilized contaminated impression guns. If our findings are supported by the results of additional research, the use of sterilization of impression guns after each use, plastic gun covers with each patient and disinfection after each use could be an effective and practical infection-prevention method for dental practices. ■ Disclosure. None of the authors reported any disclosures. This project received funding from the Indiana University School of Dentistry (IUSD) Infection Control Research Services, and the IUSD Student Research Program, Indianapolis. Patterson Dental, St. Paul, Minn., contributed the impression guns used in the study. The authors thank the staff members and students of Indiana University School of Dentistry Comprehensive Care Clinic A, Indianapolis, for their assistance and cooperation. 1. Rutala WA, Weber DJ; Centers for Disease Control and Prevention (CDC) Healthcare Infection Control Practices Advisory Committee (HICPAC). Guideline for disinfection and sterilization in healthcare facilities, 2008. “www.cdc.gov/ncidod/dhqp/pdf/guidelines/ disinfection_nov_2008.pdf”. Accessed Sept. 6, 2011. 2. Sehulster L, Chinn RY; Centers for Disease Control and Prevention (CDC); Healthcare Infection Control Practices Advisory Committee (HICPAC). Guidelines for environmental infection control in
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health-care facilities: recommendations of CDC and the Healthcare Infection Control Practices Advisory Committee (HICPAC). MMWR Recomm Rep 2003;52(RR-10):1-42. 3. Kohn WG, Collins AS, Cleveland JL, Harte JA, Eklund KJ, Malvitz DM; Centers for Disease Control and Prevention (CDC). Guidelines for infection control in dental health-care settings: 2003. MMWR Recomm Rep 2003;52(RR-17):1-61. 4. Weber DJ, Rutala WA, Miller MB, Huslage K, Sickbert-Bennett E. Role of hospital surfaces in the transmission of emerging health care-associated pathogens: norovirus, Clostridium difficile, and Acinetobacter species. Am J Infect Control 2010;38(5 suppl 1):S25-S33. 5. McCarthy GM, Koval JJ, John MA, MacDonald JK. Infection control practices across Canada: do dentists follow the recommendations? J Can Dent Assoc 1999;65(9):506-511. 6. Spach DH, Silverstein FE, Stamm WE. Transmission of infection by gastrointestinal endoscopy and bronchoscopy. Ann Intern Med 1993;118(2):117-128. 7. Weber DJ, Rutala WA. Lessons from outbreaks associated with bronchoscopy. Infect Control Hosp Epidemiol 2001;22(7):403-408. 8. Weber DJ, Rutala WA, DiMarino AJ Jr. The prevention of infection following gastrointestinal endoscopy: the importance of prophylaxis and reprocessing. In: DiMarino AJ Jr, Benjamin SB, eds. Gastrointestinal diseases: an endoscopic approach. Thorofare, N.J.: Slack; 2002:87-106. 9. Meyers H, Brown-Elliott BA, Moore D, et al. An outbreak of Mycobacterium chelonae infection following liposuction. Clin Infect Dis 2002;34(11):1500-1507. 10. Lowry PW, Jarvis WR, Oberle AD, et al. Mycobacterium chelonae causing otitis media in an ear-nose-and-throat practice. N Engl J Med 1988;319(15):978-982. 11. Weber DJ, Rutala WA. Lessons from outbreaks associated with bronchoscopy. Infect Control Hosp Epidemiol 2001;22(7):403-408. 12. Boyce J. Environmental contamination makes an important contribution to hospital infection. J Hosp Infect 2007;65(suppl 2):50-54. 13. Miller CH, Palenik CJ. Infection Control and Management of Hazardous Materials for the Dental Team. 4th ed. St. Louis: Mosby; 2010:25-36. 14. Boyce JM, Pittet D; Healthcare Infection Control Practices Advisory Committee (HICPAC); HICPAC/SHEA/APIC/IDSA Hand Hygiene Task Force. Guideline for hand hygiene in health-care settings: recommendations of the Healthcare Infection Control Practices Advisory Committee and the HICPAC/SHEA/APIC/IDSA Hand Hygiene Task Force. Society for Healthcare Epidemiology of America/Association for Professionals in Infection Control/Infectious Diseases Society of America. MMWR Recomm Rep 2002;51(RR-16):1-45. 15. Goodman ER, Platt R, Bass R, Onderdonk AB, Yokoe DS, Huang SS. Impact of an environmental cleaning intervention on the presence of methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci on surfaces in intensive care unit rooms. Infect Control Hosp Epidemiol 2008;29(7):593-599. 16. Dancer SJ, Lamb J, Girvan EK, Robertson C. Measuring the effect of enhanced cleaning in a UK hospital: a prospective cross-over study. BMC Med 2009;7:28. 17. Ghaznavi-Rad E, Ghasemzadeh-Moghaddam H, Shamsudin MN, et al. Environmental contamination in the hospital as a possible source for nosocomial infection with methicillin-resistant Staphylococcus aureus (published online ahead of print Oct. 28, 2010). Infect Control Hosp Epidemiol 2010;31(12):1302-1303. doi:10.1086/657587. 18. Spaulding EH. Chemical disinfection of medical and surgical material. In: Lawrence CA, Block SS, Reddish GF, eds. Disinfection, Sterilization, and Preservation. Philadelphia: Lea & Febiger; 1968: 517-531. 19. Rutala WA, Weber DJ. Disinfection and sterilization in health care facilities: what clinicians need to know (published online ahead of print Aug. 12, 2004). Clin Infect Dis 2004;39(5):702-709. doi:10. 1086/423182. 20. Weber DJ, Rutala WA. Environmental issues and nosocomial infections. In: Enzel RP, ed. Prevention and Control of Nosocomial Infections. Baltimore: Williams & Wilkins; 1997:491-514. 21. 3M ESPE. ImprintTM II GarantTM Quick Step Heavy Body/Light Body Impression Material System Technical Product Profile. St. Paul, Minn.: 3M ESPE Dental Products; 2002:18. 22. Beard-Pegler MA, Stubbs E, Vickery AM. Observations on the resistance to drying of staphylococcal strains. J Med Microbiol 1988; 26(4):251-255. 23. Duckworth GJ, Jordens JZ. Adherence and survival properties of an epidemic methicillin-resistant strain of Staphylococcus aureus compared with those of methicillin-sensitive strains. J Med Microbiol 1990;32(3):195-200.
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