Environmental Contamination in Healthcare Settings
Transmission of healthcare-associated pathogens to patients occurs most frequently via the transiently contaminated hands of healthcare workers. For many years, experts believed that contaminated environmental surfaces in hospitals did not play a significant role in transmission of pathogens to patients. However, recent studies have provided increasing evidence that contaminated surfaces in hospitals may be a source of transmission of pathogens.
For such transmission to occur, the following factors are necessary:
Relatively frequent contamination of environmental surfaces by pathogens;
Pathogens that are able to survive in the environment; and
Direct or indirect transmission of the pathogen to a susceptible patient.
Furthermore, if environmental contamination is epidemiologically important, then reducing environmental contamination by improved cleaning and disinfecting practices should reduce the acquisition of pathogens by patients and result in fewer infections.
Contaminated Surfaces as Sources of Nosocomial Transmission
Evidence that patients who are colonized or infected with such organisms as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), Clostridium difficile spores, Acinetobacter species, and Norovirus shed these organisms onto surfaces in their immediate environment is abundant.These pathogens can survive for days or weeks (even months for C difficile spores) on various environmental surfaces. Numerous studies have shown that healthcare workers can contaminate their hands or gloves by touching contaminated surfaces in patient rooms, and it is likely that this could result in transmission to patients.
Hayden and associatesconducted a study that provides compelling evidence that reducing environmental contamination through improved cleaning practices reduces patient acquisition of pathogens. The investigators conducted a prospective, 9-month study that included admission and daily screening of patients for VRE, and twice-weekly environmental and healthcare worker hand cultures in a medical intensive care unit. The study design included the following 4 phases:
A baseline observation period;
Education, monitoring, and feedback for housekeepers;
A washout period with no specific intervention; and
A multimodal hand hygiene intervention.
As shown in Figure 1, the proportion of environmental surfaces that were cleaned increased from a baseline level of about 50% to more than 80% in trial phases 2 to 4. The investigators also documented that VRE environmental contamination decreased significantly after housekeepers were educated and provided with feedback about their performance. Of greatest importance, VRE acquisition by patients decreased significantly when VRE contamination of surfaces was reduced. By means of multivariate analysis, the investigators showed that no other factors could explain the lower acquisition rate among patients and concluded that reduced environmental contamination was responsible for the reduced transmission of VRE to patients.
Figure. Effect of cleaning rate on VRE acquisition.
A more recent study found that additional cleaning reduced the level of environmental contamination and the incidence of new MRSA infections. Accordingly, current guidelines recommend that hospitals pay more attention to cleaning and disinfecting the environment.
The Need for Terminal Room Cleaning and Disinfecting
Numerous studies have established that previous room occupancy by patients with VRE or MRSA increases risk for acquiring these multidrug-resistant organisms in patients subsequently admitted to the same rooms.In a study by Drees and colleagues, multivariate analysis revealed that independent predictors of VRE acquisition by patients included a previous occupant who was VRE-colonized, any VRE-colonized occupant within the previous 2 weeks, and recovery of VRE from the room after it had been terminally cleaned. On the basis of these studies, experts agree that monitoring terminal room cleaning and disinfecting practices in healthcare facilities is an important element of infection control programs.
Monitoring Cleaning and Disinfecting Practices
Methods for assessing the adequacy of cleaning hospital rooms include the following:
Have housekeeping managers conduct visual inspection;
Mark high touch surfaces with a fluorescent solution and check later to determine whether the mark has been removed by housekeepers during room cleaning;
Count aerobic colonies of specimens obtained from high touch surfaces; and
Use adenosine triphosphate (ATP) bioluminescence assay to assess the cleanliness of surfaces.
Although quick and easy, visual inspection does not give reliable information about the cleanliness of surfaces.Targeting high touch surfaces in patient rooms with a fluorescent marker solution and checking the surfaces with a black light after rooms have been cleaned can determine whether the surfaces have been wiped with a liquid detergent or disinfectant well enough to remove the marker solution.Multiple studies have shown that housekeepers wipe only about 50% of surfaces targeted for cleaning.In intervention studies conducted in numerous hospitals, providing housekeepers with feedback about the results of such monitoring and educating them about the importance of their activities has led to significant improvements in the proportion of surfaces that are cleaned by housekeepers.
Sampling high touch surfaces with a moistened swab and inoculating agar media, or sampling surfaces using agar contact plates impregnated with compounds that inactivate commonly used surface disinfectants, can yield information about the degree to which aerobic bacteria have contaminated surfaces.The results of these cultures can also be used to provide housekeepers with feedback.Unfortunately, no standardized criteria for defining hospital surfaces as “clean” or “not clean” on the basis of aerobic colony counts currently exist.
Because all organic material (including microorganisms, human secretions and excretions, and food particles) contains ATP, ATP bioluminescence assay has been used to assess the level of cleanliness of surfaces in food-processing and beverage industries. More recently, such assays have been used in hospitals to monitor the adequacy of cleaning practices.With this approach, surfaces are sampled with a specialized swab that is placed in a reaction tube that contains luciferase. The tube is then placed in a luminometer, which quickly yields a digital readout of the amount of generated light, expressed as the number of relative light units. Surfaces that remain contaminated with substantial organic material yield high relative light unit readings, whereas clean surfaces yield low readings. A few studies have demonstrated that making housekeepers aware that surfaces will be tested with ATP bioluminescence assays after they are cleaned can lead to improved cleaning of surfaces in patient rooms.ATP bioluminescence assays have also been used to study the variation in performance among housekeepers in the same facility.
Suboptimal Traditional Terminal Room Cleaning Practices
The cleaning of hospital rooms following patient discharge (terminal cleaning) is often suboptimal.In many facilities, only about 50% of the surfaces in patient rooms that should be cleaned are wiped by housekeepers. This phenomenon has been documented in different types of hospitals and intensive care units as well as on general medical or surgical wards.
Inadequate cleaning and disinfecting of surfaces is usually a result of suboptimal cleaning practices, as noted above, rather than problems with the detergent or disinfectant solution that is used.Housekeepers may not wipe surfaces at all, apply an incorrect concentration of disinfectant solution, or not allow the product to remain in contact with the surface for the recommended amount of time. In most instances, terminal cleaning of patient rooms can be performed using standard hospital-grade surface disinfectant solutions at the manufacturer's recommended concentration and contact times. Currently, in the United States quaternary ammonium compounds are the most commonly used for this purpose. Newer surface disinfectants, such as activated hydrogen peroxide liquid formulations, have recently gained popularity in Canada.
Because C difficile spores are relatively resistant to standard surface disinfectants, current guidelines recommend that hospitals with highly endemic or epidemic C difficile-associated diarrhea use dilute (10%) bleach solutions for terminal cleaning of environmental surfaces in the rooms of patients with C difficile-associated diarrhea.Noroviruses, like C difficile spores, are also relatively resistant to commonly used surface disinfectants. Facilities that are experiencing nosocomial transmission of noroviruses should use dilute bleach solutions to disinfect surfaces following discharge of patients with infections caused by these organisms.
Newer Strategies for Terminal Room Decontamination
Area decontamination technologies that have been studied recently in hospital settings include microcondensation hydrogen peroxide vapor, a hydrogen peroxide dry mist system, gaseous ozone, an alcohol/quaternary ammonium power sanitizing system, and ultraviolet light room decontamination.A 10-month intervention trial looked at the decontamination of rooms with microcondensation hydrogen peroxide vapor after they were vacated by patients who had been diagnosed with C difficile-associated diarrhea. This cleaning technique significantly reduced the incidence of hospital-onset, hospital-associated C difficile diarrhea. Hydrogen peroxide vapor technology has also been used to decontaminate rooms that were vacated by patients who had been infected with norovirus or multidrug-resistant organisms, such as MRSA, VRE, Serratia, or Acinetobacter.
A study conducted at Johns Hopkins Hospital found that patients admitted to a room that had been occupied previously by a patient with VRE were significantly less likely to acquire the organism if the room had been terminally decontaminated using microcondensation hydrogen peroxide vapor technology.A hydrogen peroxide dry mist system can also substantially reduce surface contamination by bacteria, including C difficile.However, on the basis of studies published to date, this technology does not seem to be as effective against C difficile spores as hydrogen peroxide vapor technology. Further comparison of these 2 decontamination technologies is warranted. An alcohol/quaternary ammonium power sanitizing system was found in 1 study to significantly reduce MRSA and VRE contamination on hospital surfaces, but was not consistently as effective as 10% bleach solution.
Ultraviolet (UV) light has been used for years to reduce microbial contamination of air-handling systems. UV-C, particularly in the 254-nm range, destroys microorganisms by creating thymine dimers and inhibiting replication. A recent study demonstrated that an automated mobile UV-C light unit reduced bacterial contamination of surfaces by 2-3 logs (99%-99.9%). Because it has proven to be difficult for housekeepers to clean and disinfect environmental surfaces consistently according to hospital policies, these newer room decontamination technologies warrant further investigation to determine their cost-effectiveness and their role in terminal room disinfection.
Recommendations for Postdischarge Cleaning
Establish policies for which objects in patient rooms are to be cleaned/disinfected by housekeepers, and which (if any) should be cleaned by other personnel, such as nurses.
Educate housekeepers about the surfaces that should be cleaned, the appropriate concentration and contact times for each detergent/disinfectant solution in use, and the importance of room disinfection in reducing transmission of healthcare-associated pathogens.
Standard hospital-grade detergent/disinfectant solutions can be used for routine terminal room disinfection. If rates of transmission of C difficile or norovirus are high, use of a dilute bleach solution for surface disinfection in rooms vacated by patients affected by these microorganisms is recommended.
Develop methods for periodically monitoring the practices of housekeepers who are responsible for terminal room cleaning/disinfection, and provide them with feedback on their performance.
Consider using a fluorescent marking solution to target surfaces, an ATP bioluminescence assay to monitor cleanliness, or aerobic colony counts to monitor cleaning/disinfection practices. Involve infection control personnel in determining which approach to use.
For situations in which routine terminal room disinfection practices continue to be problematic despite the above measures or fail to adequately reduce transmission of pathogens that survive well in the environment (eg, VRE, C difficile, MRSA, Acinetobacter, or norovirus), consider use of a newer area decontamination technology to supplement terminal room cleaning/disinfecting protocols.