Effective disinfection of contaminated surfaces is needed to prevent transmission of healthcare-associated pathogens.Reference Donskey 1 Efforts to improve disinfection typically focus on surfaces in patient rooms that are frequently touched by the hands of healthcare workers and/or patients (eg, bed rails). Portable equipment that is shared among patients (eg, vital signs equipment, wheel chairs) can also be a potential source of pathogen dissemination.Reference Donskey 1 – Reference Peretz, Koiefman, Dinisman, Brodsky and Labay 4 For such “noncritical” equipment that comes into contact with intact skin but not mucous membranes, low- or intermediate-level disinfection is recommended after each patient use. 5 However, in busy healthcare settings, cleaning of shared medical equipment may be suboptimal.
Benign surrogate markers, such as nonpathogenic viruses and viral DNA, provide a useful tool to study routes of pathogen transmission.Reference Oelberg, Joyner, Jiang, Laborde, Islan and Pickering 6 – Reference Lopez, Gerba, Tamimi, Kitajima, Maxwell and Rose 10 For example, in a neonatal intensive care unit (ICU) a cauliflower mosaic virus DNA marker inoculated onto a telephone in 1 ICU pod was rapidly disseminated to surfaces throughout the ICU and to the hands of personnel.Reference Oelberg, Joyner, Jiang, Laborde, Islan and Pickering 6 Here, we used a similar DNA marker to test the hypothesis that portable equipment can be a vector for dissemination of microorganisms in an ICU setting.
METHODS
The Louis Stokes Veterans Affairs Medical Center is a 215-bed acute-care hospital with a 10-bed surgical intensive care unit (SICU) and a separate 16-bed medical intensive care unit (MICU). Both units have central work spaces for nurses, physicians, and ancillary staff. Portable equipment is stored within the central work space when not in use. The Louis Stokes Veterans Affairs Medical Center Institutional Review Board approved the study protocol.
We generated a 222-base-pair DNA marker from the cauliflower mosaic virus 35S promoter DNA region using the methods of Oelberg et al,Reference Oelberg, Joyner, Jiang, Laborde, Islan and Pickering 6 but a different DNA sequence was used. In brief, the 222-base-pair DNA fragment was synthesized, subcloned into a plasmid, and amplified in Escherichia coli. To produce the marker, plasmid DNA was extracted from E. coli. For detection of the DNA marker, polymerase chain reaction (PCR) was performed with forward primer CCTCAGCAATCGCAGCAAA and reverse primer GGAAGATCAATACATAAAGAGTTGAACTTC.
Sterile swabs (Fisherbrand polyester-tipped applicators, Waltham, MA) premoistened with Dey-Engley neutralizing medium (Remel Products, Lenexa, KS) were used to sample surfaces; the swab tips were transferred to tubes containing 200 µL of DNAse free water, vortexed for 2 minutes, eluted, and amplified via PCR with visualization on an agarose gel. Preliminary experiments demonstrated that 1 µg of the DNA marker inoculated onto a benchtop surface remained detectable by PCR for at least 16 weeks and was transferred to clean surfaces via handprints. The DNA marker became undetectable after a 2-minute application of bleach, but not with a similar application of 70% ethanol or a quaternary ammonium disinfectant. In addition, the marker was not consistently removed from hands with a 30-second soap-and-water wash.
To assess the potential for dissemination from portable equipment, the DNA marker was inoculated onto a selected type of frequently used portable equipment in each ICU during separate time periods. In the SICU, 1 µg of the DNA marker in 1 mL was inoculated using a pipette onto 13 Doppler ultrasound machines that are frequently used to monitor pulses of patients. In the MICU, 1 µg of the DNA marker in 1 mL was inoculated onto 3 electrocardiogram machines. Hospital personnel and patients were not aware of the study. At the time of inoculation of the DNA marker, a fluorescent marker was also placed on the portable equipment to allow an assessment of cleaning.
On days 1, 2, and 6 after inoculation of the DNA marker, swabs were used to sample high-touch surfaces within patient rooms (ie, bed rails, bedside table, call button, infusion pumps, door handles, ventilator controls, light switches, and computer keyboards), surfaces in common work areas (ie, computer keyboards, telephones, and door handles), and other portable equipment (eg, medication carts, wheelchairs, pulse oximeters). For large surfaces, a 5-×5-cm area was sampled; for smaller surfaces, the entire surface area was sampled. For each day of sampling, negative control swabs opened in the patient room but not placed in contact with surfaces were processed identically.
RESULTS
As shown in Figure 1, the DNA marker disseminated throughout both units, including to patient rooms, common areas (ie, nursing station, physician work areas), and portable equipment (ie, medication carts and bladder scanners in both units and electrocardiogram machines in the SICU). The overall percentage of sites positive for DNA was similar for each unit (SICU: 14 of 100, 14%; MICU: 11 of 128, 9%). On days 1 and 2, there was no evidence that the inoculated portable equipment had been cleaned based on the presence of fluorescent marker on the inoculated devices; on day 6, fluorescent marker was detected on the Doppler ultrasound machines in the SICU but not on the electrocardiogram machines in the MICU. All negative control swabs were negative for the DNA marker.
FIGURE. 1 Detection of a DNA marker in patient rooms, common work areas for healthcare personnel, and on portable equipment in the surgical (A) and medical (B) intensive care units. The DNA marker was inoculated onto a selected item of portable equipment (Doppler ultrasound in the surgical intensive care unit and electrocardiogram in the medical intensive care unit on day 0. *, no DNA marker was detected from any site on day 6 and there was evidence of extensive cleaning throughout the medical intensive care unit.
In the MICU, no DNA marker was detected on day 6 after inoculation. Evidence of extensive cleaning throughout the MICU included the presence of residual bleach residue on numerous surfaces and the removal of the fluorescent marker from the electrocardiogram machines.
DISCUSSION
We found that a DNA marker inoculated onto shared portable equipment in an SICU and MICU disseminated widely to surfaces in patient rooms and common work areas and to other types of portable equipment. It is likely that the hands of personnel played a major role in transfer of the DNA marker from the contaminated equipment to other sites. Our results demonstrate the potential for contaminated portable equipment to serve as a vector for dissemination of pathogens in ICU settings.
Our findings have important implications for infection control. First, there is a need for effective strategies for routine disinfection of portable equipment shared among patients. Although our infection control policies recommend cleaning of equipment shared among patients, with the exception of day 6 in the MICU, there was no evidence that the inoculated portable equipment had been cleaned based on the lack of fluorescent marker removal. Second, hand hygiene after contact with shared portable equipment could also be beneficial to reduce the risk for transmission of pathogens. Hand hygiene after contact with portable equipment would be consistent with the recommendation that hand hygiene should be performed after contact with a patient’s surroundings.Reference Sax, Allegranzi, Uçkay, Larson, Boyce and Pittet 8
Our study has some limitations. We only studied dissemination in intensive care units. Additional studies are needed in other settings. It is unclear how well the dissemination of the DNA marker correlates with pathogen dissemination. However, in laboratory testing we found excellent correlation between hand transfers of cauliflower mosaic virus DNA, bacteriophage MS-2 and non-toxigenic Clostridium difficile spores (authors’ unpublished data). The concentration of the DNA marker applied to the portable equipment was high, so our results are likely to reflect a worst-case scenario. Although the marker is rendered nondetectable by bleach, it remained detectable after exposure to 70% ethanol and a quaternary ammonium disinfectant. Thus, our findings may not correlate well with dissemination of pathogens that are killed by alcohol or quaternary ammonium disinfectants. Finally, the assay used to detect the DNA marker was qualitative and did not provide a quantitative assessment of the amount of DNA present.
In summary, our findings suggest that shared portable equipment might be an underappreciated vector for pathogen transmission in healthcare settings. Effective use of personal protective equipment, hand hygiene, and environmental disinfection may be useful to reduce the risk of transmission, but would be dependent on compliance of healthcare staff. Further research is needed to evaluate alternate methods of disinfection of portable equipment that would allow for adequate disinfection without interfering with workflow.
ACKNOWLEDGMENTS
Financial support: This work was supported by a Merit Review grant from the Department of Veterans Affairs to C.J.D.
Potential conflicts of interest: C.J.D. has received research grants from Merck, Gojo, Steris, and EcoLab. He also serves on an advisory board for 3M. All other authors report no conflicts of interest relevant to this article.
