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Disinfecting noncritical medical equipment—Effectiveness of hydrogen peroxide dry mist as an adjunctive method

Open AccessPublished:May 25, 2020DOI:https://doi.org/10.1016/j.ajic.2020.05.016

      Highlights

      • Manual disinfection of medical devices is prone to failure.
      • Dry mist hydrogen peroxide (HPDM) is a nonmanual automatized disinfection technique.
      • We evaluated the effectiveness of HPDM on ‘ready to use’ noncritical equipment.
      • HPDM substantially reduced bacterial burden on noncritical medical devices.

      Background

      Manual disinfection of medical devices is prone to failure. Disinfection by aerosolized hydrogen peroxide might be a promising adjunctive method. We aimed to assess effectiveness of dry mist of hydrogen peroxide (HPDM) on noncritical medical equipment.

      Methods

      One cycle of HPDM was applied on a convenience sample of 16 different types of "ready to use" noncritical medical devices in a closed, but nonsealed room. Of every object, 2 adjacent areas with assumed similar bacterial burden were swabbed before and after HPDM deployment, respectively. After culturing, colony forming units (CFU) were counted, and bacterial burden per cm2 calculated.

      Results

      Of 160 objects included in the study, 36 (23%) showed a CFU-count of zero both before and after HPDM use. A decrease from a median of 0.14 CFU/cm2 (range: 0.00-125.00/cm2) to a median of 0.00 CFU/cm2 (range: 0.00-4.00/cm2) (P < .001) was observed. The bacterial burden was reduced by more than 90% in 45% (95% CI: 37-53) of objects. No pathogenic bacteria were identified.

      Discussion

      HPDM reduced bacterial burden on noncritical medical items. Since cleanliness of the included "ready to use" objects was high and no pathogens were found before nebulization, the HPDM device did not increase patient safety in this setting.

      Conclusion

      HPDM nebulization can be a useful nonmanual adjunctive disinfection method in high-risk settings.

      Key Words

      BACKGROUND

      Hospitalized patients are at constant risk of acquiring multidrug resistant organisms (MDRO) or developing healthcare-associated infections. Many studies have demonstrated that environmental surfaces (eg, bedrails) and equipment (eg, stethoscopes) are a reservoir for pathogenic bacteria including MDRO.
      • Russotto V
      • Cortegiani A
      • Raineri SM
      • Giarratano A
      Bacterial contamination of inanimate surfaces and equipment in the intensive care unit.
      • Schabrun S
      • Chipchase L.
      Healthcare equipment as a source of nosocomial infection: a systematic review.
      • Matsuo M
      • Oie S
      • Furukawa H
      Contamination of blood pressure cuffs by methicillin-resistant Staphylococcus aureus and preventive measures.
      • de Gialluly C
      • Morange V
      • de Gialluly E
      • Loulergue J
      • van der Mee N
      • Quentin R
      Blood pressure cuff as a potential vector of pathogenic microorganisms a prospective study in a teaching hospital.
      • Lestari T
      • Ryll S
      • Kramer A
      Microbial contamination of manually reprocessed, ready to use ECG lead wire in intensive care units.
      • Obasi C
      • Agwu A
      • Akinpelu W
      • et al.
      Contamination of equipment in emergency settings: an exploratory study with a targeted automated intervention.
      In a comprehensive review, Otter et al. summarize evidence that contaminated surfaces contribute to the transmission of hospital pathogens.
      • Otter JA
      • Yezli S
      • Salkeld JA
      • French GL
      Evidence that contaminated surfaces contribute to the transmission of hospital pathogens and an overview of strategies to address contaminated surfaces in hospital settings.
      It was also shown that patients who are admitted to a room previously occupied by a patient colonized or infected with vancomycin-resistant enterococci (VRE), methicillin-resistant Staphylococcus aureus (MRSA) or other pathogenic bacteria, are at increased risk of acquiring this specific pathogen from the previous patient.
      • Drees M
      • Snydman DR
      • Schmid CH
      • et al.
      Prior environmental contamination increases the risk of acquisition of vancomycin-resistant enterococci.
      • Huang SS
      • Datta R
      • Platt R
      Risk of acquiring antibiotic-resistant bacteria from prior room occupants.
      • Nseir S
      • Blazejewski C
      • Lubret R
      • Wallet F
      • Courcol R
      • Durocher A
      Risk of acquiring multidrug‐resistant Gram‐negative bacilli from prior room occupants in the intensive care unit.
      • Shaughnessy MK
      • Micielli RL
      • DePestel DD
      • et al.
      Evaluation of hospital room assignment and acquisition of Clostridium difficile infection.
      To reduce bacterial burden of surfaces and equipment, effective cleaning and disinfection is required.
      Disinfection describes a process that eliminates many or all pathogenic microorganisms, except bacterial spores, on inanimate objects.
      • William H
      • Rutala PD
      • Weber DJ
      and the other Healthcare Infection Control Practices Advisory Committee (HICPAC)
      Noncritical items—items that come in contact with intact skin but not mucous membranes—such as medical equipment (eg, bedpans, blood pressure cuffs, crutches) and environmental surfaces (eg, bedside tables) are disinfected with a low-level disinfectant.
      • William H
      • Rutala PD
      • Weber DJ
      and the other Healthcare Infection Control Practices Advisory Committee (HICPAC)
      However, disinfection procedures are highly operator-dependent and prone to failure when executed manually.
      • Boyce JM.
      Modern technologies for improving cleaning and disinfection of environmental surfaces in hospitals.
      Therefore, nonmanual automatized disinfection techniques, such as aerosolized hydrogen peroxide (HP) or ultraviolet light, are an interesting alternative or adjunctive infection control measure.
      Airborne HP is active against a wide range of microorganisms, including bacteria, yeasts, fungi, viruses, and spores. It can either be applied in aerosolized (eg, dry mist) or vaporised form. Passaretti et al. showed that the risk of acquiring an MDRO in general, and a VRE specifically, was reduced by 64% and 80%, respectively after room disinfection with HP.
      • Passaretti CL
      • Otter JA
      • Reich NG
      • et al.
      An evaluation of environmental decontamination with hydrogen peroxide vapor for reducing the risk of patient acquisition of multidrug-resistant organisms.
      Horn et al. demonstrated that the odds ratios of acquiring an extended-spectrum beta-lactamase producing Gram-negative bacterium, an MRSA, a VRE, and Clostridium difficile after introducing HP vapour for terminal decontamination of patient rooms were 0.06, 0.53, 0.05, and 0.65, respectively.
      • Horn K
      • Otter JA
      Hydrogen peroxide vapor room disinfection and hand hygiene improvements reduce Clostridium difficile infection, methicillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, and extended-spectrum beta-lactamase.
      Medical equipment, which is commonly removed from the patient room before terminal room disinfection, was shown to be often contaminated by pathogens.
      • Russotto V
      • Cortegiani A
      • Raineri SM
      • Giarratano A
      Bacterial contamination of inanimate surfaces and equipment in the intensive care unit.
      • Schabrun S
      • Chipchase L.
      Healthcare equipment as a source of nosocomial infection: a systematic review.
      • Matsuo M
      • Oie S
      • Furukawa H
      Contamination of blood pressure cuffs by methicillin-resistant Staphylococcus aureus and preventive measures.
      • de Gialluly C
      • Morange V
      • de Gialluly E
      • Loulergue J
      • van der Mee N
      • Quentin R
      Blood pressure cuff as a potential vector of pathogenic microorganisms a prospective study in a teaching hospital.
      • Lestari T
      • Ryll S
      • Kramer A
      Microbial contamination of manually reprocessed, ready to use ECG lead wire in intensive care units.
      It comes into direct contact with the patient or is placed in the immediate patient environment. Moreover, some parts of the medical equipment may be difficult to disinfect manually. These items might therefore benefit from an adjunctive, standardized, nonmanual disinfection step to further reduce bacterial burden before being passed to the next patient. With the present study, we aimed to investigate the effectiveness of applying a single cycle of HP aerosolized disinfection of noncritical medical items.

      METHODS

      Study setting and objects

      The study was conducted at the University Hospital Zurich, Switzerland, a 950-bed tertiary-care teaching hospital with 6 intensive care units (ICU).
      We included 16 different noncritical object types, 8 from general wards and ICUs each. A convenience sample of noncritical objects "ready to use," that is disinfected according to internal University Hospital Zurich guidelines with aldehyd- (Kohrsolin FF) or alcohol based (Meliseptol) disinfectants, were collected throughout the hospital. Healthcare professionals (HCP) were not aware of the study execution, and the routine disinfecting procedure had not been supervised. Ten items of every object type were analysed.

      Dry mist hydrogen peroxide nebulization procedure

      A programmable device (HyperDRYMist, Modulator Micro-Nebulizer 99MB by 99Technologies, Switzerland) generating a dry mist of hydrogen peroxide, with a particle size of < 1 µm, was used. The disinfecting solution consists of purified water, 6.6% w/w hydrogen peroxide, 60 mg/l silver cations and a set of undisclosed proprietary co-formulants, which synergistically enhance biocidal action. The bactericidal properties result from the oxidative action of hydroxyl radicals on the lipid membrane, DNA, and other essential cell components of microorganisms, and the effect of silver cations that reverse membrane polarity and inhibit protein synthesis and cytoplasmic enzyme activity. The disinfectant is micro-nebulized as a dry aerosol that accesses all surfaces exposed to air. Disinfection happened in a nonclimatized room of 60 m3 with closed, but unsealed doors and windows. The HPDM micro-nebulizer was placed in a corner of the room, and the study objects were placed at a distance of >2 m from the machine. One cycle consisted of 10 minutes "dissemination time" (ie, time of active nebulization), 45 minutes "exposure time" (ie, time of ongoing activity and progressive decay of hydrogen peroxide), and 15 minutes "ventilation time" (ie, time of clearing residue levels of hydrogen peroxide by ventilating the room). A total of 3 ml/m3 of disinfectant solution was nebulized, corresponding to 140 ppm of hydrogen peroxide.

      Sampling and microbiology

      Swab samples of 160 objects were collected before and after nebulization. Shape and dimension of swabbed area was individualized according to object (Fig 1, and Appendix A). The largest possible area making a rectangle or round shape was swabbed. Hypothesising that swabbing removes bacteria, 2 adjacent areas with assumed equal bacterial burdens (area A and B) were swabbed before and after nebulization.
      Fig 1
      Fig 1Example of study object. The swabbed area of all study objects was divided in area A and area B of same size and hypothetically same bacterial burden. Areas A and B were swabbed before and after nebulization alternately.
      Sampling was performed with moistened eSwabs comprising 1 millilitre of Liquid Amies medium. Specimens were stored at 4°C and processed within 24 hours after sampling. After vortexing the swabs in Amies medium for 15 seconds, an aliquot of 500 µl Liquid Amies medium per sampled object was plated on a 5% sheep blood agar plate. The agar plates were incubated 72 hours at 36°C, and colony forming units (CFU) of aerobic bacterial growth per agar plate were counted manually.
      Identification of both opportunistic and pathogenic bacteria (eg, S. aureus, Enterobacteriaceae ssp., Pseudomonas aeruginosa, and Enterococci ssp.), as well as environmental flora was performed by experienced laboratory technicians in the on-site laboratory. After culturing aerobic bacteria on sheep blood agar, subculturing was performed on sheep blood and MacConkey agar. For species identification catalase and oxidase test, followed by latex agglutination test for S. aureus identification and multicolor system Enterotubes for identification of Enterobacteriaceae ssp. were used.

      Bacterial burden

      For samples with CFU too numerous to count, CFU count was set to 500 per sampled area. Bacterial burden was calculated in CFU/cm2. According to Dancer et al. we defined a “clean object” as an object with <5 CFU/cm2.
      • Dancer SJ.
      How do we assess hospital cleaning? A proposal for microbiological standards for surface hygiene in hospitals.
      The “percentage decrease” of CFU after nebulization was calculated as follows:
      Percentagedecrease=100(CFUafternebulizationCFUbeforenebulization×100)


      If bacterial burden before nebulization was zero any increase of bacterial burden after nebulization was set as “percentage decrease” = −100%.

      Categorization of objects

      For subgroup analysis we grouped the objects according to: (1) ward type, that is objects collected on general wards vs objects collected on ICUs; (2) material, that is plastic, metal and fabric; (3) Flat, “easy to clean” objects vs angled, nonflat “difficult to clean” objects (Table 1).
      Table 1Bacterial burden of all objects before nebulization
      ObjectsNo. of included objectsSwabbed area in cm2Ward typeMaterial“Easy to clean” vs “Difficult to clean”CFU/ cm2 before nebulization, median (range)P value (Wilcoxon rank-sum test)*
      Blood pressure cuff10285GWPE0.22 (0.01-0.73).614
      ECG electrodes1035GWMD1.23 (0.00-14.29).001
      Infusion pump (inside)10108ICUMD0.01 (0.00-0.11).004
      Infusion pump (outside)1054ICUPE0.13 (0.00-0.67).631
      Infusion stand10145GWME0.04 (0.00-0.40).079
      Monitor10127ICUPE0.01 (0.00-0.13).003
      Oxygen regulator1020ICUPE0.20 (0.00-0.70).865
      Patient's phone108GWPE1.50 (0.00-8.50).001
      Pulse oximeter104ICUPD1.00 (0.00-125.00).014
      Remote control1050GWPE1.68 (0.04-10.00).003
      Stethoscope diaphragm108GWPE0.00 (0.00-4.00).021
      Suction pump1022ICUPE0.27 (0.09-3.82).076
      Syringe pump1093ICUPD0.03 (0.00-0.47).107
      Thermometer108ICUPD0.25 (0.00-0.50).382
      Tourniquet1052GWFD0.42 (0.00-1.88).126
      Wheelchair10108GWME0.00 (0.00-1.13).001
      All objects1600.14 (0.00-125.00)
      NOTE. Baseline bacterial burden (CFU/cm2) of all 160 objects before HPDM nebulization. CFU counts of samples with CFU too numerous to count were set to 500 CFU per sampled area. CFU too numerous to count were present on 2 ECG electrodes, 2 pulse oximeters and 2 remote controls. * Wilcoxon rank-sum test was used to compare bacterial burden between objects.
      cm2, square centimetres; HPDM, hydrogen peroxide dry mist; D, “difficult to clean” object; E, “easy to clean” object; F, fabric; ICU, intensive care unit; GW, general ward; M, metal; No., number; P, plastic

      Statistical analysis

      Wilcoxon rank sum test was used to compare bacterial burdens between objects. Wilcoxon signed ranks test was used for paired comparison of bacterial burden before and after nebulization. After dichotomizing results of percentage of decrease in ≥90% and <90% (“90% decrease”), Fisher's exact test was used to test for differences between object types, materials, and bacterial burden before nebulization. Significance was set as P <.05. All statistical analyses were performed with STATA version 15 (Stata Corp., College Station, TX).

      RESULTS

      Object type and bacterial burden before nebulization is shown in Table 1. We found high median colonization on ECG electrodes, patients’ phones, pulse oximeters and on remote controls, and low median colonization on the inside of infusion pumps, monitors, stethoscope diaphragms, and wheelchairs. Before nebulization, no bacterial growth was detected in 25.6% of objects. Eight (5%) objects were “not clean,” that is ≥5 CFU/cm2, according to Dancer et al.’s "microbiological standards for surface hygiene in hospitals" (2 ECG electrodes, 2 patients’ phones, 2 pulse oximeters, 2 remote controls).
      • Dancer SJ.
      How do we assess hospital cleaning? A proposal for microbiological standards for surface hygiene in hospitals.
      In all 124 objects with detectable colonization, only skin or environmental flora was identified and no pathogenic bacterium was found. For raw data of all sampled items see Appendix B.
      Of all 160 objects, 23% (n = 36) did not show bacterial contamination before and after nebulization. Table 2 shows median bacterial burden before and after nebulization, and median "percentage decrease" due to nebulization. Fig 2 shows median CFU before and after nebulization per object type, Appendix C shows results for every single object. Across all objects, we found decrease from a median of 0.14 CFU/cm2 (range: 0.00-125.00) to a median of 0.00 CFU/cm2 (range: 0.00-125.00, P < .001). All but 6 objects (insides of infusion pump, stethoscope diaphragms, syringe pump, thermometer, tourniquet, and wheelchairs) showed a statistically significant CFU decrease. After nebulization, 99% (n = 159) of objects were “clean,” according to Dancer's “microbiological standards for surface hygiene in hospitals”
      • Dancer SJ.
      How do we assess hospital cleaning? A proposal for microbiological standards for surface hygiene in hospitals.
      and 63% (n = 100) showed no bacterial growth. In 45% of objects (95% confidence interval (CI): 37-53) the decrease of CFU was more than 90%.
      Table 2Bacterial burden of included objects before and after nebulization
      ObjectsNo. of included objectsCFU/cm2 before nebulization, median (range)CFU/cm2 after nebulization, median (range)Percentage decrease, median (range)> 90% decrease, %P value (Wilcoxon signed ranks test)*
      Blood pressure cuff100.22 (0.01-0.73)0.06 (0.01-0.15)69.88 (-55.56-94.23)30.014
      ECG electrodes101.23 (0.00-14.29)0.14 (0.00-5.71)85.79 (0.00-100.00)30.006
      Infusion pump (inside)100.01 (0.00-0.11)0.00 (0.00-0.06)0.00 (-100.00-100.00)30.499
      Infusion pump (outside)100.13 (0.00-0.67)0.00 (0.00-0.15)100.00 (0.00-100.00)70.008
      Infusion stand100.04 (0.00-0.40)0.00 (0.00-0.03)100.00 (0.00-100.00)70.008
      Monitor100.01 (0.00-0.13)0.00 (0.00-0.02)0.00 (0.00-100.00)40.047
      Oxygen regulator100.20 (0.00-0.70)0.00 (0.00-0.20)100.00 (0.00-100.00)80.007
      Patient's phone101.50 (0.00-8.50)0.25 (0.00-3.75)82.64 (0.00-100.00)40.006
      Pulse oximeter101.00 (0.00-125.00)0.00 (0.00-4.00)100.00 (0.00-100.00)80.008
      Remote control101.68 (0.04-10.00)0.46 (0-00-3.20)64.58 (0.00-100.00)20.006
      Stethoscope diaphragm100.00 (0.00-4.00)0.00 (0.00-0.00)0.00 (0.00-100.00)30.084
      Suction pump100.27 (0.09-3.82)0.09 (0.00-0.64)81.67 (0.00-100.00)40.006
      Syringe pump100.03 (0.00-0.47)0.01 (0.00-1.31)34.09 (-1933.33-100.00)40.299
      Thermometer100.25 (0.00-0.50)0.00 (0.00-0.25)100.00 (-100.00-100.00)60.051
      Tourniquet100.42 (0.00-1.88)0.08 (0.00-2.81)28.79 (-563.64-100.00)40.575
      Wheelchair100.00 (0.00-1.13)0.00 (0.00-0.00)0.00 (0.00-100.00)20.158
      NOTE. Bacterial burden before and after HPDM nebulization of objects * Wilcoxon signed ranks test compares bacterial burden (in CFU/ cm2) from objects before nebulization with bacterial burden (in CFU/cm2) after nebulization.
      CFU, colony forming unit; CI, confidence interval; cm2, square centimetres; ECG, electrocardiogram; No., number.
      Fig 2
      Fig 2Median bacterial burden before and after nebulization. Median bacterial burden (CFU/cm2) before and after HPDM nebulization of objects. (CFU, colony forming unit; cm, centimetre; ECG, electrocardiogram).
      Before nebulization, objects from general wards had higher CFU counts compared to objects from ICUs (median 0.10 CFU/cm2 [range: 0.00-4.00] vs 0.29 CFU/cm2 [0.00-14.2; P =.033]). Nebulization of objects from general wards and ICUs lead to a “90% decrease” in 35% (CI: 25-46) and 55% (CI: 43-66; P =.033), respectively. We did not find differences in nebulization effectiveness when comparing objects of different materials, nor when comparing “difficult to clean” and “easy to clean” objects (data not shown). In “nonclean” objects with a bacterial burden > 5 CFU/cm2 (n = 8), the HPDM nebulization resulted in a median decrease of 89% CFU (data not shown)

      DISCUSSION

      Our study, investigating a nonmanual disinfection method of noncritical medical equipment, demonstrated that 23% of the objects "ready to use" did not show any bacterial contamination and 95% were "clean" (ie, <5 CFU/cm2) before HPDM nebulization. Furthermore, including all objects into analysis, HPDM led to a median CFU decrease of 79% (IQR: 0-100) and reduced more than 90% of CFU in 45% (72/160) of objects.
      The objects of noncritical medical equipment included in our study were "ready to use" and showed a low bacterial burden. Compared to other studies assessing contamination after standard disinfection procedures we found a 10-100 fold lower median bacterial burden of only 0.14 CFU/cm2.
      • Attaway 3rd, HH
      • Fairey S
      • Steed LL
      • Salgado CD
      • Michels HT
      • Schmidt MG
      Intrinsic bacterial burden associated with intensive care unit hospital beds: effects of disinfection on population recovery and mitigation of potential infection risk.
      • Schmidt MG
      • Anderson T
      • Attaway 3rd, HH
      • Fairey S
      • Kennedy C
      • Salgado CD
      Patient environment microbial burden reduction: a pilot study comparison of 2 terminal cleaning methods.
      • Chan HT
      • White P
      • Sheorey H
      • Cocks J
      • Waters MJ
      Evaluation of the biological efficacy of hydrogen peroxide vapour decontamination in wards of an Australian hospital.
      Moreover, no pathogenic bacteria were identified on the included medical devices. Still, 8 out of 160 objects (5%) were "not clean" (ie, ≥5 CFU/cm2) according to established criteria,
      • Dancer SJ.
      How do we assess hospital cleaning? A proposal for microbiological standards for surface hygiene in hospitals.
      even though all objects should have undergone a disinfection procedure according to our hospitals’ guidelines. Heavy contamination is a surrogate marker of an insufficient cleaning and disinfection process and points out the critical role of the human factor in the cleaning procedure,
      • Joseph AC
      • Olivier S-C
      From discovery to design: the evolution of human factors in healthcare.
      We found that in 45% of objects HPDM nebulization led to a more than 90% decrease in CFU. In heavily contaminated objects, the HPDM nebulization resulted in a median decrease of 89% CFU. Other studies also reported good effectiveness of HP systems. Weber et al. reviewed the effectiveness of HP systems for terminal room decontamination and found several studies (predominantly using vaporized HP) demonstrating reduction of multidrug-resistant organisms by a percentage between 86% and 100%.
      • Weber DJ
      • Rutala WA
      • Anderson DJ
      • Chen LF
      • Sickbert-Bennett EE
      • Boyce JM
      Effectiveness of ultraviolet devices and hydrogen peroxide systems for terminal room decontamination: focus on clinical trials.
      A systematic review by Falagas et al. found that disinfection with terminal cleaning vs HP reduced the percentage of contaminated environmental sites from 39% to 28.3% vs 2.2%, respectively.
      • Falagas ME
      • Thomaidis PC
      • Kotsantis IK
      • Sgouros K
      • Samonis G
      • Karageorgopoulos DE
      Airborne hydrogen peroxide for disinfection of the hospital environment and infection control: a systematic review.
      The studies included in these 2 reviews might not be entirely comparable to our study, as all but 1 study targeted pathogenic bacteria only (eg, MRSA, Serratia sp.)—in our study, on the other hand, we did not find pathogenic bacteria on any of our objects before the study procedure. Additionally, most of the included studies in the aforementioned reviews used vaporisation systems, which were reported to be more effective than aerosolized HP.
      • Fu TY
      • Gent P
      • Kumar V
      Efficacy, efficiency and safety aspects of hydrogen peroxide vapour and aerosolized hydrogen peroxide room disinfection systems.
      ,
      • Holmdahl T
      • Lanbeck P
      • Wullt M
      • Walder MH
      A head-to-head comparison of hydrogen peroxide vapor and aerosol room decontamination systems.
      The vast majority of previous studies evaluating HP effectiveness investigated noncritical environmental surfaces and not medical devices. We identified only a single study testing effectiveness of HP disinfection on medical devices using Bacillus spores as indicators.
      • Andersen BM
      • Rasch M
      • Hochlin K
      • Jensen FH
      • Wismar P
      • Fredriksen JE
      Decontamination of rooms, medical equipment and ambulances using an aerosol of hydrogen peroxide disinfectant.
      This study especially assessed decontamination of the inner part of medical equipment (ie, ventilators or suction pumps) and found that 3 diffusion cycles of HP dry aerosol had a sporicidal effect in 62% of tested items, with an increase to 100% effectiveness when devices were ventilated.
      Compared to environmental surfaces, noncritical medical devices might be more difficult to clean. In our study, many of the included objects, eg. pulse oximeters, were angled and not flat. CFU decrease did not differ between these probably "difficult to clean" objects compared to "easy to clean" objects. One particular advantage of HP disinfection is that all surfaces exposed to the HP-containing air are disinfected irrespective of their shape. After expiration of the dissemination time, the concentration of HP is evenly distributed in the whole room and distance between object and HP device is negligible. “Difficult to clean” objects might therefore benefit the most from this nontouch disinfection technique.
      Our study has limitations. First, we included “ready to use” medical devices and assumed prior disinfection according to our hospitals’ guidelines, but the execution of the disinfection procedure could not be verified. This, however, better represents a real-life situation. Second, we included 36 objects into the analysis of this real life study that did neither show contamination before nor after nebulization. That, in turn, has led to an underestimation of HPDM nebulization efficacy. By performing a sensitivity analysis excluding these 36 objects, we found that the median percentage decrease was 100% and the 90%-decrease was 58% (data not shown). Third, we did not use neutralizers to inactivate residual disinfectants potentially inhibiting bacterial growth, thus potentially leading to an underestimation of bacterial contamination before nebulization. Still, the relative reduction of CFU count is unchanged, as aerosolized hydrogen peroxide does not require the use of neutralizers, as it breaks down into water and oxygen relatively rapidly (within 30 minutes on a surface).
      • Sandle T
      Avoiding environmental monitoring ‘false negatives’: overcoming disinfectant residues with culture media neutralisers.

      CONCLUSIONS

      In conclusion, our study testing an easy-to-use HPDM device on noncritical medical items in a “real life setting,” shows relevant reduction of bacterial burden after HP disinfection. Of interest, bacterial burden before nebulization was very low in our hospital and we did only identify nonpathogenic bacteria on the included objects. Thus, effectiveness of the HPDM system to reduce pathogenic bacteria could not be proven. Nevertheless, noncritical medical equipment has been shown to be contaminated with pathogens in many other settings. The effectiveness of HP systems to reduce contamination with MRSA, C. difficile and other pathogens was demonstrated by other authors and there is no rationale to assume a different efficacy between pathogenic and nonpathogenic bacteria.
      • Bartels MD
      • Kristoffersen K
      • Slotsbjerg T
      • Rohde SM
      • Lundgren B
      • Westh H
      Environmental meticillin-resistant Staphylococcus aureus (MRSA) disinfection using dry-mist-generated hydrogen peroxide.
      • Mosci D
      • Marmo GW
      • Sciolino L
      • et al.
      Automatic environmental disinfection with hydrogen peroxide and silver ions versus manual environmental disinfection with sodium hypochlorite: a multicentre randomized before-and-after trial.
      • Piskin N
      • Celebi G
      • Kulah C
      • Mengeloglu Z
      • Yumusak M
      Activity of a dry mist-generated hydrogen peroxide disinfection system against methicillin-resistant Staphylococcus aureus and Acinetobacter baumannii.
      In view of the fact that medical devices can act as fomites, HPDM nebulization might act as “safety-net” in disinfection processes on high-risk wards like ICUs or during outbreaks. It could for example be used to routinely disinfect noncritical medical equipment after patient discharge or during the patient's absence from the room due to a medical procedure. Alternatively, noncritical medical equipment could be pooled in a small room allowing an even shorter disinfection cycle time due to the low room volume. Use of the present HPDM device exhibits less logistic issues compared to vapour HP techniques as no room sealing is needed and room occupation dead-time is usually less than 1 hour. Compatibility of HP disinfectants with medical equipment has to be assessed before application. Further research is warranted to investigate if HPDM disinfection of noncritical medical devices reduces MDRO transmission in routine use within real-world settings.

      Acknowledgments

      We would like to thank Olga Janzen and Holger Giray for their assistance in collecting the medical equipment throughout the hospital. Thanks to all the wards and ICUs who provided us with their medical equipment for HPDM nebulization.

      Appendix. SUPPLEMENTARY MATERIALS

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