ABSTRACT
Steam disinfection is a trusted method of decontamination and leave no residues, but yet has not been commonly applied for hospitals environment decontamination, hence we aimed to evaluate whether steam mop is an effective device for against pathogens on natural contaminated hospital floors (polyvinyl chloride, PVC) and artificially contaminated (Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii and Candida albicanson) PVC and cloth. The number of microorganisms was significantly reduced after the procedure (p < 0.05) on all hospital floors. Steaming for 15, 10 and 5 seconds could achieve full elimination of all high-, moderate-, and low concentration microorganisms on PVC, respectively, whereas 10, 5 and 10 seconds for cloth. High-, moderate-, and low concentrations microorganism on PVC were completely killed after the first, second and third routine mopping respectively. These results imply that steam mop could be an efficient and environment-friendly alternative for hospitals floors and cloth towels disinfection.
Introduction
The transmission of pathogens between hosts via contaminated surfaces frequently occurs and is a common mode in the spread of infectious diseases. Hospital surfaces are major repositories of various health care-associated pathogens and multi-drug resistant organisms, such as methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii and yeast Candida albicans, which have been shown to survive on dry surfaces for several weeks to a month [Citation1]. Therefore, decontamination of hospital environment surfaces is necessary to ensure the safety of health care workers and patients and crucial to decrease the dissemination of multi-drug resistant pathogens.
The floor is one of the most severely contaminated environmental surfaces in hospital settings [Citation2–4], while efforts to improve disinfection are usually focused on surfaces that are frequently touched by the hands of persons but not floors. However, there is increasing evidence suggesting that floors could be an underestimated source of pathogen transmission [Citation5–8]. Additionally, the incomplete decontamination of reusable cloth towels could create a germ breeding ground in medical institutions. It’s reported that typical hospital laundering practices with disinfectants are not sufficient to remove all microorganisms and spores from towels [Citation9]. These evidences imply that substantial efforts are required to improve the cleaning and disinfection of floors and cloth towels.
A diverse range of traditional liquid chemical disinfectants has been applied for cleaning hospital floors and cloth towels to control the spread of microbes and the development of antimicrobial resistance. However, the properties of disinfectants and human factors make these methods unsafe and inefficient. These drawbacks warrant the development and introduction of optimized decontamination schemes.
Some newer methods, such as hydrogen peroxide, magnetic disinfectant, steam technology with ultra-microfiber are increasing studied [Citation10–16]. Steam disinfection is a trusted disinfection method that human and environment friendly, simple, inexpensive and effective, has been used as the preferred method for disinfecting heat-resistant medical items [Citation17]. Steam has also been increasingly introduced into hospitals for environmental surfaces and textiles cleaning in recent years [Citation12,Citation13,Citation15,Citation18], but it has not been widely applied because the equipment needed to generate it was too bulky and immobile, and the knowledge about equipment, methods, frequencies and cost are still limited. Steam mop is a common household device that equipped with decreased size of steam generators, has make steam technology much more practical in environmental surface disinfection. To date, there have been few reports on the employment of steam mop to disinfect hospital floors and cloth towels, evaluating the effectiveness of such device in hospital settings would be helpful to improve the application of steam disinfection technology for hospital environment disinfection.
Hence, the objective of the current study was to determine the effectiveness of a steam mop against nature organism contamination present on hospital floors under real-life conditions, and the effectiveness of decontamination by applying the steam mop to different contaminated levels of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Acinetobacter baumannii and Candida albicans on polyvinyl chloride (PVC) test surfaces and cloth in a laboratory study, to provide an alternative to chemical disinfectants.
Materials and methods
Steam mop setup
The disinfection device used for this study was a steam mop (P8, Shark, America，) with a multifunctional design supporting fixed-point continuous steam injection, one-button replacement of the floor towel and two-sided use of the floor towel. The isosceles triangular cleaning head were used to perform the experiments, and a corresponding sterile towel was affixed to the cleaning head according to the manufacturer’s instructions. Before the experiments, the device was filled with tap water, connected to the power and activated. The steam temperature selected was 95–100°C, which was thought to be safer for the operator and less damaging to the PVC plastic floor. The steam mode was high (steam output amount: 28 g/min).
Figure 1. The steam mop used in this study.
Evaluation of the inactivation effect under real-life conditions
Hospital floors of different types of rooms were chosen for steam mop application
This study was performed in a tertiary teaching hospital with over 2400 beds in Guangzhou, China. The effectiveness of steam mop decontamination was evaluated on floors of different types representing probably different levels of contamination. A total of 42 floor sites were selected to receive the treatment: ICUs (7), general wards (6), consulting rooms (3), CT/X-ray/MR rooms (3), outpatient hall (2), dressing room (4), washroom (4), and operating room (3), as showed in .
Table 1. Microbial load estimation before and after steam mop application on different hospital floors (42 samples) (CFU/cm2).
Experimental methodology
The same cleaning protocols were applied for all floors. Specifically, one single floor towel sterilized by autoclave was used for each floor to avoid cross-contamination: the operator installed the dry cleaning towel on the body of the steam mop and started up the mop until the steam temperature of the outlet reached 95–100°C, started mopping (passing the mop over the floor, proceeding from top-to-bottom and from left-to-right, overlapping the passes and ensuring that there were no areas had not been passed by mop), approximately 2 square metre floor surfaces around each bed unit or room, and finally recycled the floor towel for sterilization. The cleaned floor was allowed to air dry for 10 min before collecting samples.
All samples were collected in triplicate from floor surfaces with an area of 25 cm2 using sterile swabs before and after disinfection processes to evaluate the efficiency of the cleaning protocols with a steam mop on each floor surface. Each sterile swab was soaked in 10 ml of PBS with sufficient shaking, and then, 1 ml of the solution was aspirated using a disposable sterile syringe and inoculated on a Petri dish containing BHI agar. The cultures were incubated at 37°C for 48 h, and then colony-forming units (CFU) growth was quantified.
Evaluation of the inactivation effect on selected pathogens under experimental conditions
Microbial species
The microorganisms used for the experimental decontamination tests were obtained from the Department of Laboratory Medicine of the hospital and included the gram-positive bacterium Staphylococcus aureus (ATCC 6538), the gram-negative bacterial pathogens Escherichia coli (ATCC 25,922), Pseudomonas aeruginosa (ATCC 15,442), Acinetobacter baumannii (ATCC 17,978) and the yeast Candida albicans (ATCC 10,231). These microorganisms were chosen because they are usually used as controls in susceptibility tests of antimicrobial agents, have different cell wall structures and are associated with hospital-acquired infections. All strains were grown in BHI broth at 37°C to mid-exponential phase, centrifuged and resuspended in PBS. The suspensions were quantified through the optical density to obtain an original suspension with 108 colony-forming units.
Validation of disinfection effectiveness for PVC test surfaces
PVC coupons were used as the test surfaces. These coupons were cut from PVC plastic floors that are usually used in hospitals, then washed and sterilized in a steam autoclave before contamination. All tests consisted of microorganisms spread on sterile PVC coupons that quantified the viable population after decontamination.
The high contaminated surfaces usually serve to prove a bactericidal reduction capacity of log10 > 5 [Citation19]. In the present study, suspensions with 108, 105 and 102 colony-forming units (CFU)/mL of each microorganism species were produced for the preparation of standardized contaminated surfaces. One hundred microlitres of each suspension was dried on PVC test surfaces with dimensions of 5 × 5 cm to generate standardized highly (107 ~ 108 CFU), moderately (104 ~ 105 CFU) or lowly (10 ~ 102 CFU) contaminated surfaces.
We conducted two different types of experiments to determine the inactivation effect of steam mop. First, the surfaces were decontaminated using the steam mop by direct contact without the act of wipe at 95–100°C. Each individual experiment required 10 test surfaces: 1 surface reserved as a negative control and 9 surfaces inoculated with microorganisms. Of the 9 inoculated surfaces, 8 were treated with the steam disinfection system (for either 1, 3, 5, 10, 15, 20, 25, 30 s), and one was left untreated to determine the success of bacterial contamination (). Second, the surfaces were decontaminated using the same cleaning protocols mentioned above, each test surface was mopped three times in succession, and a sample was collected after each time, each individual experiment mentioned above was performed 3 times independently. All samples were collected from the contaminated 5 × 5 cm dimensions using sterile swabs before (one untreated surface) and after (8 treated surfaces) disinfection processes. The subsequent processing was same as above.
Figure 2. Microbial load of contaminated PVC coupons after decontamination by direct contact of the steam mop at different times.
Validation of disinfection effectiveness for cloth
Cloth similar to the material type of the cloth towels used for cleaning floor were prepared with dimensions of 1 × 5 cm and sterilized in a steam autoclave before contamination. One hundred microlitres of suspension containing 108, 105 and 102 colony-forming units of each bacterium was soaked in sterile cloth and dried for decontamination, which served as the bacterial cloth. Three pieces of bacterial cloth were adhered to the outside of the cleaning head towel and were sterilized at 95–100°C for different times (), synchronously, 1 sterilized cloth served as a negative control, and 1 bacterial cloth was left untreated to determine the success of bacterial contamination. After the treatment, each cloth was soaked in 10 ml of PBS with sufficient shaking, 1 ml of the solution was then aspirated using a disposable sterile syringe and inoculated on a Petri dish containing BHI agar, then incubated at 37°C for 48 h to quantify the viable population.
Figure 3. Microbial load of contaminated cloth after decontamination by direct contact of the steam mop at different times.
Statistical analysis
A paired sample t-test was performed to compare the microbial load before and after steam mist decontamination. A p value of <0.05 was considered statistically significant.
Results
The disinfectant efficiency of using this device on hospital floors in different areas is shown in . The steam mop significantly reduced the microbial colony count (p < 0.05) on different room floors and almost completely removed the microorganisms present on all surfaces, thus demonstrating the high-efficiency decontamination capability of the steam mop.
All positive control samples of each experiment revealed approximately 107-108 (highly contaminated surface), 104-105 (moderately contaminated surface) and 10–102 (lowly contaminated surface) CFU/25 cm2, which were confirmed as the colony counts applied to the surfaces. The efficiency of steam mopping over the reduction of microorganism viability on each tested PVC surface and cloth is shown in . The time needed for complete cell killing varied with the microorganism species and concentrations, as well as the PVC coupons and cloth. The higher the concentration is, the longer disinfection time is required.
As described in , the low concentrations of a diverse array of microorganisms on PVC coupons were completely killed within 3 s by steam contact, except for the Escherichia coli by steam contact within 5 s. All moderate concentrations of a diverse array of microorganisms on PVC coupons were reduced to 0 by steam contacting within 5 s, but 10 s of steam contact was needed for Staphylococcus aureus. Complete killing of high concentrations was achieved within 10 s of treatment by steam contacting PVC coupons, but 15 s was needed for Escherichia coli.
For the highly, moderately and lowly contaminated cloth by all these three microorganisms, 10, 5 and 3 s of steam contact were needed for complete killing, respectively ().
shows that the low concentrations of all microorganisms on PVC coupons were completely killed after the first mopping, and complete killing of moderate and high concentrations was achieved after the second and third mopping, respectively.
Figure 4. Microbial load of contaminated PVC coupons after steam mopping three times.
Discussion
The contamination of health care environments with a range of pathogens may lead to undesirable health care-associated infections. A study proved that a live microorganism inoculated onto floors could transfer to the hands of patients or objects that are subsequently touched by hands [Citation3]. The nonslip socks worn by hospitalized patients were frequently contaminated with MRSA and VRE [Citation20]. Additionally, cloth towels that usually washed and disinfected in-house and stored for reuse are easily become potential vehicles for the transmission of pathogens themselves. It was found that Staphylococcus can survive in cotton cloths for 19–21 days [Citation21,Citation22]. MRSA that cause severe life-threatening infections have been isolated from hospital reused towels [Citation23]. The isolation of opportunistic bacterial pathogens from floors and reused towels places importance on utilising a robust and effective disinfection protocol to eliminate such pathogens, especially disinfectant and antibiotic resistant pathogens, which usually cannot be completely killed by chemical disinfectants.
Manual cleaning using traditional chemical disinfectants is still a common method for the decontamination of floors and reusable cloth towels in most hospitals. However, exposure to traditional chemical disinfectants poses risks to medical staff, patients and the environment due to their volatility and capacity for causing irritation [Citation5]. Additionally, manual control of the concentration of chlorine and the immersion time may lead to incomplete disinfection and pose hospital infection risks. Furthermore, the long-term use of chemical disinfectants could enhance bacterial resistance, resulting in a decrease in the disinfection effect [Citation24]. Other disadvantages also include corrosiveness to metals, discoloring of fabrics and relative instability.
The efficacy of newer methods like steam technology is currently being studied. Some novel steam vapor systems have proven effective for killing specific pathogens or their biofilm on different surfaces [Citation13,Citation15,Citation16,Citation25]. The novel cleaning method by using microfiber and steam technology has also been employed for cleaning operating room and intensive care unit [Citation11,Citation12]. However, this promising technology has not been commonly used for hospital environment surfaces disinfection because of the poor accessibility of portable steam disinfection device, and evaluate the quality of such technology applying under different conditions still has been limited.
Steam mops currently available on the market provide an infrastructure for the application of steam disinfection technology and thus provide a possibility for attempts to clean and disinfect the surfaces of the hospital environment to prevent environmentally borne transmission. This study we focused on assessing the efficacy of demotic steam mop to inactive a certain pathogen at different concentrations on floor (PVC) and cloth. The results demonstrated that steam mop is effective in reducing microorganisms on PVC floor and cloth in a short time, despite the time needed for treatment varied among microorganisms. Routine cleaning protocols with steam mops could reduce microorganisms to an acceptable level of safety on hospital floor surfaces. The treatment time for Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa and Candida albicans was longer in compared with previous studies [Citation13,Citation25], possibly due to the lower sterilized temperature and different material of tested surfaces used in our study, the thermal conductivity and specific volume heat of different material could led to the different temperature of steam on surfaces. Therefore, the exposure time protocols at an appropriate temperature should be determined for eliminating a target microorganism on a certain subjected materials.
Steam technology removes the risk of negative effects on the environment because the high steam temperature can directly kill bacteria without adding any additional toxic chemicals except water, a step forward compared to chemicals with high toxicity for human beings, and the environment, also, the cost of water is less expensive than chemical disinfectants. The steam mop used in this study produce the saturated steam composing almost entirely of water in the vapour phase, is hotter and drier than typical unsaturated team, which is often laden with small droplets of liquid water [Citation25]. The saturated steam usually poses no more risk to a variety of materials than normal liquid disinfectants, and there was no notable water residue remaining on the floor after use of the steam mops [Citation26]. Importantly, heat could nearly inactivate all vegetative cells including the disinfectant and antibiotic resistant pathogens at hospital environment, because the physiological mechanisms drive for repairing damage caused by heat and antimicrobial chemicals in microorganisms are entirely separate [Citation27]. The risk of cross-resistance would be eliminated by steam disinfection, instead of persistent transmission under the selective pressures exerted by the heavy use of various classes of antibiotics and chemical disinfectants at hospitals [Citation28].
Our study demonstrated that the time of treatment for PVC or cloth by steam is far less than that of the chemical disinfectants, which require 30 min of continuous sterilization for floors and 30 min of ‘thorough soaking’ for reusable cloth towels, time savings could provide additional opportunities to save costs by improving the range of cleaning tasks. The reusable cloth cleaning towels are not needed taken down for manual cleaning but directly cleaning and disinfect by steaming for 10 s before and after usage, could be effective to killed a broad range of pathogenic microorganisms, and convenient for hospital application. These results suggest that the decontamination of both different hospital floors and cleaning towels by this device may be an alternative to available chemicals for disinfection of environmental surfaces. Although the use of steam mops to disinfect hospital environment has not received much attention, and there have been few evaluations of the disinfection effects in the hospital environment, considering that steam technology has been widely used for other health items [Citation29–31], we can imply its use for hospital floors decontamination. In the future study, the exposure time protocols could also be developed for elimination of microorganisms on other hospital environment surfaces, such as curtains, tables and bed unit.
It is worth noting that the steam mop reached temperatures of 100°C in this study, which is effective at eliminating vegetative bacteria but would not be of sufficient heat lethality to eliminate spore-forming organisms, such as Clostridium and Bacillus general [Citation32]. These spores have thick and dense cell walls and are highly resistant to both environmental stresses and chemical disinfectants, especially high temperatures, thus require higher steam temperatures for elimination [Citation32]. Therefore, future study is needed to determine the time of treatment required for steam mop to rapid total elimination of these high concentrations (>104 CFU) microorganisms and spore-forming organisms at higher steam temperatures (>100°C).
It is not denied that steam cleaning could pose risks for inhaling aerosols of pathogenic microorganisms, which were resuspended from floor by mechanical collision and heating. It is not clear how much of the aerosols that occurs during the process of steam mopping. In this study, we explored the potential impact of steam cleaning on resuspension of bacteria or fungi from PVC floors by comparing the air bacteria counts of before disinfection and during the disinfection process. Both the process of steam mopping and damp mopping slightly increased the bacteria counts, but not significantly when compared with those of before disinfection (data not showed). Personal protection (such as wearing gloves, goggles and protective masks) of operators and ward opening windows for ventilation could be helpful to reduce these risks. In addition, there are still risks to operators (and others) from inadvertent steam exposure that may cause burns to the skin and mucous membranes; thus, rigorous training in the correct use of the device is needed. Furthermore, the plug-in steam mop is not easy to use in the place without or far away from power. All these shortcomings of steam might limit its wide application in hospital cleaning routine. More accurate assessment of microorganism aerosols and cost of steam mop are needed in future research, and the device design should be optimized to easy and safe for use in hospital settings.
In conclusion, steam mop achieved a high reduction in the microbial load on representative hospital floors. The time needed for complete cell killing at the experimental conditions varied with the microorganism species, contaminated concentrations and tested materials. The application of steaming (without wipe action) for 15, 10 and 5 s could achieve full elimination of the in vitro growth of high-, moderate-, and low contaminated concentrations microorganisms involved in health-associated infections on PVC surfaces, respectively, and 10, 5 and 10 s for cloth, respectively. High-, moderate-, and low concentrations microorganism on PVC coupons were completely killed after the first, second and third routine mopping, respectively. Overall, steam mopping is a promising alternative disinfection protocol in hospitals for reducing the risk of infection transmission. The design of steam mop needs to be further improved for easier use in hospital settings.
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