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Evidence shows that bacteria on floors can be resuspended into the air with a potential of inhalation, swallowing, or contamination of surfaces and hands.
Environmental surfaces that receive frequent hand contact (i.e. high touch surfaces) are understood to be a potential vector for certain pathogens. Floors are not generally considered to contribute to the risk of pathogen dissemination in a similar manner, nor the associated infection risk. Consequently, floor hygiene is considered of low importance when assessing the risk of transmission of pathogens. Research in the last decade is shaping a clearer picture of how floors act as a reservoir for pathogens and may contribute to infection risk. This article reviews evidence on floors and how they may play a role as a reservoir in the chain of infection.
Chain of Infection and Recent Research:
To establish the potential risk of floors in contributing to infection risk, floors need to be:
Epidemiological models based on studies of air movement have established a framework for understanding how pathogenic microorganisms move from the floor to off-the-floor surfaces where hand contact can occur. Studies of floors which were intentionally seeded with non-pathogenic viruses demonstrated that these viruses can move from floors to hand contact surfaces in the same patient room and in other rooms on the same ward, demonstrating the potential for transmission. Observational studies looking at patient behavior in health care have demonstrated moments of risk occur that can result in rapid transfer of pathogens from the floor to the patient’s bed space, and testing of surfaces in several studies have shown that transfer of pathogenic bacteria from floors to the patient bed does occur in certain circumstances, but the subsequent link to causing human infection has not been demonstrated so far.
Floors are Non-Critical Surfaces in Health Care Facilities:
In health care, floors are classified as non-critical surfaces because they presumably only contact footwear and intact skin when people walk barefoot on the floor, meeting the Spaulding definition of a non-critical surface. While non-critical surfaces that receive frequent hand contact
(i.e. high touch surfaces such as door handles, light switches, hand rails, etc) are a potential source of pathogen transmission for certain environmentally transmissible pathogens, floors are generally not touched by hands and have not been implicated as playing a significant role in an outbreak in the literature. Thus health care guidelines for environmental infection control recommend cleaning, if referenced at all. Donskey observed that while there is strong evidence that floors are a potential source of pathogen dissemination, the link with human infection is not well investigated thus far, with no randomized studies investigating floor hygiene as an infection control practice, limiting the motivation health care facilities might have to invest in better floor hygiene programs.
Studies Investigating Floor Contamination with Pathogenic Organisms
The evidence of floor contamination with pathogenic organisms is strong and a range of studies have demonstrated that floors are typically heavily contaminated with bacteria and frequently contamination with health care associated infection (HAI) causing pathogens including Methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus (VRE)and Clostridioides difficile (C diff).
One of the strongest studies is a five hospital study that swabbed floors for MRSA, VRE, and C diff. C diff was most commonly found on floors, present in ~50% of patient rooms where the patient had C diff infection (CDI). Brown investigated environmental contamination with C diff spores and found floors were twice as likely to be contaminated as bedrails, with floor contaminated in 87.5% of samples versus 41.7% of bedrail samples. Floors were also found to have ~16 times more C. diff spores than bedrails (69.4 versus 2.7 per sample).
In a review article, Suleyman notes that floors are often heavily contaminated with C diff, VRE, and MRSA, are an underappreciated source of transmission of pathogens and for patients with C diff, and the environment has been shown to contain a high number of spores, with higher counts of spores on the floor than other surfaces. In a recent study testing surfaces in rooms with patients being treated for COVID-19, Redmond tested surfaces in rooms for the presence of SARS-CoV-2 RNA and found that floors were more commonly contaminated with the virus RNA than the high touch surfaces they were also testing (33.3% versus 15.8%).
Munoz-Price investigated improving operating room hygiene and found that Gram negative bacilli were present in 63% of baseline floor samples and 41.6% of intervention samples. Floors were positive for Staphylococcus aureus or Enterococcus species in 63.6% of baseline samples and 66.7% of intervention samples despite use of a phenolic disinfectant on floors.
Studies Investigating Pathogen Transfer to/from Floors and Other Surfaces
Several studies have included an investigation of whether pathogens can be transferred from floors to other surfaces. Munoz-Price noted that after floor contact objects routinely were picked up and placed or moved onto horizontal surfaces or the patient, including anesthesia tubing and IV tubing, indicating a potential for floor-to-hand contamination.
Deshpande assessed objects coming in contact with floors and found that 41% of these patient’s rooms had objects in contact with the floor that would also be touched by the patient or health care workers’ hands. These objects included personal items, medical devices, and bed linens or towels. On finding such objects on the floor in a patient room, the auditor picked up the object to show whether bacterial transfer could occur. They found a high rate of contamination with hands or gloves positive for MRSA (18%), VRE (6%), and C. diff (3%) after picking up the object, demonstrating the potential for dissemination of pathogens from the floor to hand contact surfaces near the patient bed.
In transmission studies, Koganti showed that a bacteriophage seeded onto the floor moved rapidly to hand contact surfaces in the room and other rooms on the ward. Galvin and Mahida investigated different aspects of how patients with contaminated footwear have the potential to transfer bacteria from the floor onto the bedsheets. Testing of the bedsheets showed that a significant number of bacteria, including pathogenic bacteria, were transferred to the bedsheets by the patient walking on the floor and then climbing into bed.
Studies Investigating Floor Hygiene and/or the Impact on Air Contamination
Several studies have investigated the relationship between floor hygiene and air contamination with bacteria. Ayliffe showed that bacteria levels in air samples rose ~10X during contaminating events (such as shaking a blanket) or during floor disturbance (such as walking across the floor or exercising on the floor) before returning to baseline levels within 1 hour. Gupta discussed that a significant portion of airborne bacteria in intensive care units were bacteria from the floor that had been re-dispersed into the air, with a high number of the floor bacteria being skin-associated.
Hambraeus found bacteria carrying particles on the floor were redispersed by walking, mopping, and the blowing of air on the floor (i.e. facility ventilation). Walking gave the highest re-dispersal factor, which was three times higher than blowing of air and 17 times higher than mopping. Ciofi-Silva studied the relationship between floor cleaning and air contamination with norovirus and found the level of air contamination was higher after using a neutral cleaner than when using a disinfectant, indicating the potential to disseminate a virus from the floor into the air, especially when using a neutral cleaner on the floor.
Anderson investigated four floor cleaning methods including: dry mopping, spray mopping (spraying detergent solution on the floor and then mopping), moist mopping (prewetted flat mop), and wet mopping (high amount of detergent solution applied to floor followed by dry mopping to pick up excess liquid) and found a high amount of variation in the initial bacteria level on the floor and that all floor cleaning methods increased the level of bacteria in the air.
Studies Investigating Air Movement and Floors:
Weipublished a review article discussing the airborne dissemination of pathogens including how breathing, talking, sneezing, and coughing, expel respiratory droplets containing viruses into the environment, how these droplets can move >6 meters when expelled at high velocity and ultimately the droplets tend to settle on horizontal hand contact surfaces or the floor. Wei also discussed the mechanics of air movement associated with the presence of people and how a person’s thermal plume causes air from knee level to rise above the head and how walking and room air circulation can reduce the size of the thermal plume, but when a person is motionless, the plume quickly reestablishes itself. The study by Wei demonstrates a model that explains how pathogenic organisms on the floor can become airborne and either settle on hand contact surfaces, or be inhaled or swallowed if the air containing the organisms enters the breathing zone.
This article reviewed relevant evidence surrounding floors and their potential role in causing human infections. Evidence of floor contamination with high levels of pathogenic organisms is strong. There is moderate evidence showing that bacteria on floors can be resuspended into the air with a potential of inhalation, swallowing, or contamination of surfaces and hands. There is a growing need for studies investigating whether this reservoir of microorganisms can result in human infection, which could provide evidence of a need for more rigorous floor hygiene practices, especially in healthcare facilities.
Peter Teska is a global infection prevention application expert at Diversey Holdings, Ltd., a leader in providing smart sustainable solutions for cleaning and hygiene. He is a member of the Diversey Hygiene Academy and can be reached at firstname.lastname@example.org. For more information, visit www.diversey.com.