On the basis of the 2007 Taiwan Nosocomial Infections Surveillance System report, respiratory infection is the third highest nosocomial infection encountered in medical center intensive care units (Centers for Disease Control, Department of Health, Taiwan, ROC, 2008). Respiratory infection also is the most significant cause of infection mortality among all nosocomial infections (Klevens et al., 2007). Invasive treatment equipment, such as ventilators, manual ambulatory bag, humidifiers, and nebulizers, reportedly cause some 14.7% of infections (Dima et al., 2007; Rosenthal et al., 2006). Small-volume nebulizers (SVNs) are in widespread use among patients with pulmonary diseases in the hospital. SVN-delivered aerosol treatments, which can reduce symptoms of acute and chronic respiratory tract diseases rapidly, are used frequently by nursing staff (Le Brun, de Boer, Heijerman, & Frijlink, 2000; Rau, 2005). Research has indicated aerosol treatment may cause bacterial translocations and respiratory tract infections (Mastro et al., 1991). Studies have further revealed that nebulizers might pose high contamination rates (Lin, Peng, Chen, Ye, & Huang, 2007). Contaminated air may be delivered directly into a patient's lower respiratory tract as aerosol through an artificial airway. Bacteria-contaminated nebulizers will increase chances of patient infection.
Respiratory infections caused by SVNs are related to aerosol particulate size and the path by which aerosol particles enter the trachea. If aerosol particles are less than 5 μm, they may infect bronchiole and pulmonary alveolus. When patients are fitted with endotracheal tubes, respiratory tract infections are even more likely because bacterial contamination risk through aerosols of the lower respiratory tract increases (Cohen, Cohen, Pomeranz, Czitron, & Kahan, 2005). SVN contamination may cause bacterial translocation from the oral to lower airways (Monforte et al., 2005). Nebulizers also have high contamination rates after usage (Blau et al., 2006; Cohen et al., 2006; Lin et al., 2007). The contamination rate has been shown to increase when the nebulizers are contaminated by microorganisms (Cohen et al., 2005; Monforte et al., 2005). Home-used nebulizers are frequently contaminated with multiple bacteria, mostly Gram-negative bacilli (Cohen et al., 2006). Cohan et al. (2006) found that 66.7% of home-used nebulizers were contaminated in their study, whereas Blau et al. (2006) found a similar ration (65%) in their study. Causes of nebulizer contamination may be linked to the use of contaminated reagents or devices as well as environmental contamination (Denton et al., 2003; Jakobsson, Onnered, Hjelte, & Nystrom, 1997; Mastro et al., 1991; Reboli et al., 1996). The Center of Disease Control and Prevention nosocomial pneumonia prevention guide provides the following recommendations for using SVNs: (a) If the nebulizer is used on one patient only, the nebulizer must be cleaned, sterilized, and rinsed with aseptic water (while sterilizing with chemical disinfectants) and then desiccated. (b) Rinsing nebulizers in tap water is not recommended. (c) Before applying the nebulizer to different patients, it should be sterilized using a high-level sterilization method (Category IB). (d) Apply only aseptic liquid during aerosol treatment. (e) Use the same medicine as much as possible. If multiple medicine is required, follow manufacturers' directions (Category IB; Tablan, Anderson, Besser, Bridges, & Hajjeh, 2004). The above recommendations, however, do not address the proper method of nebulizer cleaning and sterilization. SVN expiry dates, cleaning methods, and rinsing and sterilizing needs are based on medical and clinical center policies. Hence, easier and more scientifically based methods are needed for efficacy in treating patients who use SVNs.
Pervious studies addressing nebulizer cleaning and sterilization revealed that soaking and rinsing nebulizers 30 seconds with tap water can effectively reduce the population of bacteria inside the nebulizers (Rosenfeld, Joy, Nguyen, Krzewinski, & Burns, 2001). However, such procedures are difficult to perform in the current hospital setting because hospital tap water often contains microorganisms that are highly likely to contaminate nebulizers (Mastro et al., 1991). Furthermore, no direct evidence has shown such the efficacy of such a method when used in a hospital (Denton et al., 2003; Lester, Flume, Gray, Anderson, & Bowman, 2004). Research on nebulizer cleaning methods has found that soaking the nebulizer in a 75% alcohol and 3% hydrogen peroxide solution for 10 minutes will decrease bacteria contamination significantly and that soaking in sterile distilled water provides only limited decontamination effectiveness (Fang, 2007). To date, there remains no consensus regarding an adequately effective cleaning and sterilizing method for SVNs. In a population-based survey of home nebulizer use among patients, the most common cleaning reagent used was found to be tap water (Rosenfeld, Emerson, & Astley, 1998). In the interest of patient safety, nursing staff should provide secure and safe medical equipment and treatment. This study was designed to explore the SVN cleaning efficacy of different reagents and application methods. Independent variables included cleaning reagents and cleaning methods. Cleaning efficacy was the dependent variable (Figure 1).
This study used an experimental research design. In the study, tap water and sterile distilled water were used as cleaning reagents. Moreover, to find out which cleaning method had the highest efficacy, SVNs were divided into three different cleaning method groups: soak, rinse, and soak then rinse. Cleaning efficacy was defined as bacteria count after cleaning. Researchers purchased nebulizers directly from the manufacture (Everest Med-Equip Trading Co., Ltd., Taiwan), and all nebulizers were used only once. This study was reviewed and approved by the hospital's institutional review board.
Thirteen groups were used in this study, each with 10 SVNs. Noncontaminated nebulizers were assigned to six groups (three for tap water cleaning and three for sterile distilled water cleaning). SVNs used in the remaining seven groups were contaminated with Escherichia coli (one group was assigned with noncleaning, three groups for tap water cleaning, and three groups for sterile distilled water cleaning). After cleaning, researchers examined the bacteria cultures of 130 SVNs (see Figure 2).
Bacteria Contamination and Cleaning Procedures
The bacteria contamination procedure was as follows. Nebulizers were immersed for 10 minutes in 600 ml of sterile distilled water containing 106 cells/ml E. coli. The designated cleaning procedure was performed immediately afterward. Three different cleaning methods were applied to the SVNs, namely, (a) soak nebulizer for 10 minutes, (b) rinse nebulizer for 30 seconds, and (c) soak nebulizer for 10 minutes then change water rinse for 30 seconds. Cleaning reagents used included tap water and sterile distilled water.
Bacteria Culture and Quantification
All bacteria culture procedures of this research used microbiological methods (Willey, Sherwood, & Woolverton, 2008). In brief, bacteria were cultivated in Luria-Bertani agar broth (Difco Laboratories, Detroit, MI, USA) and incubated at 37°C overnight. Bacterial growth was monitored turbidimetrically by measuring optical density at 600 nm, where an optical density unit of 1.0 corresponded to 3 × 108 cells/ml. The researcher conducted the experiment on a laminar flow cabinet in a microbiological laboratory. After completing the designated cleaning procedure, the researcher took and examined bacteria culture samples from the reservoir cup interior, annular tube, T connector, and mouthpiece. Sterile cotton sticks were used to swab these four SVN areas and transfer the swabbed material to culture plates. Bacteria counts were performed after incubation at 37°C. The colony was recorded as the mean number of colony-forming units (CFU) per culture surface. Sites with <10 CFU were identified as clean, sites with 10-100 CFU as mildly contaminated, and sites with >100 CFU as contaminated (Cohen et al., 2006).
Analysis and Statistics
Researchers used the "Nebulizer Cleaning and Culturing Data Sheet" to record data. Entries include date of experiment, regent used, cleaning method, examined items, and colony numbers. Data were shown as mean values with standard deviations and analyzed using SPSS (Version 10.0; SPSS Inc., Chicago, IL, USA). A one-way analysis of variance (ANOVA) was used to analyze residual bacteria counts and cleaning efficacy among three cleaning methods. Researchers used multivariate ANOVA to measure the effects of cleaning reagents and methods on cleaning efficacy. p ≤ .05 was used to designate statistical significance.
The Comparative Cleaning Efficacy of Tap Water and Sterile Distilled Water
Researchers used a one-way ANOVA to analyze the efficacy of the two different cleaning reagents (Table 1). The noncontaminated group was found free of bacterial colonies, and the contaminated group with no cleaning group had a higher bacterial count than other groups (p < .001). The reservoir cups in the sterile distilled water cleaning group showed bacteria number increases that were significantly higher than that in the tap water cleaning group (155.90 ± 155.21 vs. 84.69 ± 83.04; p = .031).
Comparative Cleaning Efficacy Among the Three Cleaning Methods
Table 2 shows the cleaning efficacy among the three different cleaning methods used in this study. Results revealed a significant difference in cleaning efficacy (p < .001). Cleaning efficacy of the soak-then-rinse method revealed a significantly lower bacteria count than achieved in either the soak-only or the rinse-only groups. Bacteria numbers in the reservoir cup and annular tube were not significantly different between the soak-only and the rinse-only groups. However, the rinse method achieved a cleaning efficacy superior to the soak method in the T connector (8.84 ± 8.47 vs. 41.71 ± 31.46) and mouthpiece (16.49 ± 21.92 vs. 68.05 ± 63.38) areas.
Cleaning Reagents and Cleaning Methods Affect Cleaning Efficacy
Researchers used a two-way multivariate ANOVA to analyze differences among the cleaning efficacies of reagents (sterile distilled water and tap water) and cleaning methods (soak, rinse, and soak then rinse). Table 3 shows the interactions between cleaning reagents, and methods were not significantly different (Wilks Λ value = .752, p = .060). Results also revealed that different cleaning reagents (Wilks Λ value = .772, p = .009) and different methods (Wilks Λ value = .044, p < .05) affected cleaning efficacy. Tap water achieved better cleaning efficacy than sterile distilled water on the reservoir cup. The cleaning efficacy of soak-then-rinse method was superior to both soak-only and rinse-only methods. The rinse-only method was found more efficacious than the soak-only method.
SVNs are widely used to treat patients with respiratory diseases in hospitals and home settings. Incorrect cleaning procedures may cause microorganism contamination. Although many hospitals have developed guidelines for nebulizer sterilization, no standards exist for cleaning home-used disposable nebulizers. There has been little prior research work to compare the relative SVN cleaning efficacy of tap water and sterile distilled water. Our results found that tap water cleaning can reduce the number of bacteria to 0.74%-2.29% (Table 1; mouthpiece, from 4524.25 to 29.56; reservoir cup, from 3704.55 to 84.69). These results are similar to the research findings of Rosenfeld et al. (2001). They found that tap water rinse effectively eliminated contamination in 17 of 19 nebulizers. On the other hand, using sterile distilled water to clean SVNs reduced the number of bacteria to 0.64%-5.73% (mouthpiece, from 4524.25 to 28.07; reservoir cup, from 3704.55 to 155.90). This result differs from that of Fang (2007), who found that sterile distilled water was able to reduce average bacteria numbers to 23%. The reason for this difference may be number of contamination times. In Fang's research, nebulizers were contaminated 28 times before cleaning. In our study, each nebulizer was contaminated only once to reduce the possibility of other interferences. Because we found no bacteria in any of the uncontaminated nebulizers, we effectively demonstrated that our operating process did not introduce additional contaminates into nebulizers. Both tap water and sterile distilled water can reduce by more than 90% the number of bacteria in nebulizers, and statistics did not show a significant difference between the effectiveness of tap water and sterile distilled water. The two reagents used in this study were cleaning agents rather than disinfectants. Nebulizer cleaning agents decrease microorganism numbers and cannot eliminate microorganisms completely. This study showed tap water and sterile distilled water to present similar cleaning efficacies.
Table 2 revealed that cleaning nebulizers using the soak-only method reduced bacteria numbers to 1.50%-5.07% (mouthpiece, from 4524.25 to 68.05; reservoir cup, from 3704.55 to 187.77). Nebulizers cleaned using the rinse-only method reduced bacteria numbers to 0.36%-3.84% (mouthpiece, from 4524.25 to 16.49; reservoir cup, from 3704.55 to 142.14). The soak-then-rinse method achieved bacteria reduction numbers as low as 0.01%-0.84% (T connector, from 2051.80 to 0.11; reservoir cup, from 3704.55 to 30.97). Table 3 demonstrates statistically significant differences among the three cleaning methods. The soak-then-rinse method generates significantly better results than the other two methods. The soak-only and the rinse-only methods also differ from one another in terms of cleaning efficacy in different parts of the nebulizer. Although there were no noticeable differences between the two in the reservoir cup and annular tube areas, T connector and mouthpiece areas showed that the rinse-only group achieved significantly lower bacteria numbers than the soak group. However, on this point, our findings differed from Fang (2007), who found no significant difference in cleaning efficacy in these areas between the two cleaning methods. This difference is likely attributable to the different cleaning methods used. In Fang's study, soak was the only procedure used for cleaning. In our study, the soak-then-rinse method increased cleaning time and added a new cleaning procedure. The reservoir cup still showed a bacteria count higher than that in other nebulizer sections. This result is similar to that of Blau et al. (2006), who found the reservoir cup to have a higher contamination rate than the mouthpiece. Such indicates that the reservoir cup may incorporate surface flaws that increase resistance to cleaning. Materials used in reservoir cup construction may be another reason behind disparate cleaning efficacies between soak-only and rinse-only methods in different nebulizer sections.
Limitations of this study include the testing of cleaning efficacy only once and the obtaining of results under laboratory conditions only. Such may not adequately capture home cleaning practices. Results should be validated further through clinical testing and additional study.
In conclusion, this study demonstrated that both tap water and sterile distilled water have a similar efficacy, reducing bacteria counts by 90% or more. The soak-then-rinse method was demonstrated significantly superior to the other two methods tested. Results suggest that SVN cleaning procedures should consistently use the same cleaning reagent. In practice, we recommend cleaning all nebulizer parts after each use. Soaking nebulizers for 10 minutes then rinsing 30 seconds in tap water is an appropriate method to remove bacteria colonies.
The authors have no financial relationship with any commercial entity holding an interest in the subject of this article.
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