Setting and design
The study was conducted in a 160-bed long-term care facility in the upper Midwest. One floor of 34 beds is devoted to rehabilitation and 126 beds provide skilled long-term care. The study involved a pretest-posttest design with repeated measures. Thirty-six months of pretest data were compared with 12 months of posttest data. Environmental surfaces and facility-wide rates of infection and hospitalization were the units of analysis.
The ultraviolet disinfection protocol
The Xenex Germ-Zapping Robot™ (Xenex Disinfection Services) is a portable device that produces a high intensity flashing light, delivered in millisecond pulses, from across the entire disinfecting spectrum (from 200 to 320 nm). This germicidal UV energy passes through the cell walls of bacteria, viruses and bacterial spores. The DNA, RNA, and proteins are damaged by four mechanisms. Photohydration (pulling water molecules into the DNA), photosplitting (breaking the DNA), and photodimerization (improper fusing of DNA bases) all prevent cell replication. In addition, photo crosslinking causes irreversible cell wall damage and cell death [12].
ATP hygiene measure
Luminometers are commonly used to measure food contamination and to monitor the effectiveness of surface cleaning and demonstrate reliable performance for measuring surface cleaning effectiveness [13]. A swab sample of high-touch surfaces placed in the luminometer (Hygiena EnSURE V.2, Scigiene Inc.) measured the quantity of light generated by a bioluminescence reaction. Results, expressed as Relative Light Units (RLU), indicate the amount of adenosine triphosphate (ATP) in the sample. The presence of ATP indicates that a surface may harbor microorganisms and support bacterial growth but measures come from anything organic in the sample [14]. The ATP swabs are not able to detect UV disinfection. The organism may be killed or rendered inactive but the ATP molecule is not removed during UV exposure. The luminometer is not meant to replace microbial testing, but can provide results in 15 s. Sampling for ATP was done before cleaning and repeated again after the room had received both cleaning and ultraviolet room disinfection.
Cultures
To gain a better understanding of the effectiveness of the ultraviolet disinfection on true microbial contamination, culture swab samples were collected for culture from 30 consecutive discharge rooms at three time points: baseline; post cleaning, and post ultraviolet disinfection. This yielded a total of 90 cultures from 30 rooms, and three locations for each of the three different time points. Established laboratory-based procedures were used and included swabbing blood agar plates in a four quadrant fashion and placement into an O2 incubator for 48 h. Gram stain, morphology, and colony counts of gram-positive bacilli from 1+ to 4+ were reported.
Rates of infection and hospitalization for infection
Each incidence of hospital acquired and nursing home acquired infection and hospitalization for an infection for each of the 48 months was obtained from records maintained by the facility. Infection rates were expressed per 1,000 resident-care days per month. Infections were considered hospital acquired if symptoms started less than 48 h after transfer from the hospital to the nursing home. Nosocomial infections were defined by the onset of symptoms 48 h or more after admission to the nursing home [15]. To get a better estimate of hospitalizations for nursing home acquired infections, we excluded residents who were readmitted to the hospital within 30 days for infection.
Procedures
When a resident was discharged, one of two trained research staff were notified to collect baseline ATP measures from five high-touch surfaces: bed rail, call light button, bedside table surface, bathroom toilet seat, and right bathroom faucet handle. The housekeeping staff then cleaned the room for approximately 40 min and high-touch surfaces were wiped down using a stabilized sodium hypochlorite and detergent solution cleaning agent.
Following cleaning and prior to ultraviolet disinfection, surfaces were prepared so that they were exposed to ultraviolet light during its operation. Call buttons, blood pressure cuffs, and telephone handsets were turned to face the device’s location. Dresser drawers, closet doors, and shower curtains were opened and blinds were closed. The ultraviolet disinfection device was preset to beam ultraviolet light for 5 min each time it was turned on and staff left the room within 15 s of the device being turned on. Figure 1 shows the three locations the device was placed for 5 min of exposure in each location. Prior to exposure in the second bedroom location some surfaces were again shifted to maximize exposure of surfaces to the pulsed light emitted by the device (e.g. handset of phone turned over). Multiple locations for the device allowed for the high intensity UV-C light to reach a different shielded surface each time, minimizing shadowed areas. For UV-C light to be effective, line-of-sight exposure is desired. However, reflected ultraviolet light has also been shown to be effective under certain circumstances in achieving decontamination of areas not exposed to direct light [16, 17]. ATP samples were again collected after the cleaning and ultraviolet disinfection were both completed.
For 30 consecutive rooms, swab samples of high-touch surfaces were collected after resident discharge at threetime points: baseline; post cleaning, and post ultraviolet disinfection. Two assistants were trained to collect culture samples of three high-touch surfaces using consistent and sterile procedures: the enabler bar, overbed table, and right bathroom faucet handle. The sterile swab was placed into a balanced isotonic solution to maintain organism viability (BD Sterile Pack Swab for surface and equipment sampling), stored in a lab refrigerator at a temperature range of 35 to 39 °F, and sent to the laboratory within 8 h. The variation in elapsed time from collection to deliver to the lab varied from 5.5 to 8 h with the first culture swabs taken at baseline having the longest elapsed time to lab delivery.
Data analysis
ATP and culture plate data were highly skewed and analyzed with the median, range and non-parametric statistics. Differences in ATP RLU’s from baseline to post cleaning and ultraviolet disinfection were compared using the median and Wilcoxon signed rank tests. Differences in microbial cultures between baseline, post cleaning, and post ultraviolet disinfection were described using frequencies and percentages. The Cochran’s Q non-parametric test for related samples was used to compare differences in culture results between the three time points.
Our analysis of infection rates used ratios to account for the lack of independence between rates of nursing-home acquired and hospital-acquired infections. Hospital-acquired infections have become more common as medical treatments and patient complexity have increased and are the sixth leading cause of death in the United States [18, 19]. Our data showed substantial increases each year in hospital acquired infections between 2012 and 2015. Nursing homes are federally mandated to consider an infection nursing-home acquired if symptoms emerge 48 h or more after hospital discharge [15]. This siloing of infection attribution is problematic because the incubation periods for many common viral and bacterial illnesses are longer than 48 h [20, 21]. The reciprocal relationship between hospital and nursing home acquired infection has been demonstrated [22]. Using a model based on actual patient and agency data to simulate the movement of infection between hospitals and nursing homes, the influence of hospitalization on nursing home MRSA prevalence and nursing homes influence on hospital MRSA prevalence levels was demonstrated [22]. Hence, the hospital acquired infection rates were analyzed relative to nosocomial infection rates.
To analyze differences in infection rates from pre to posttest, the independent variables were the 36 months of pre disinfection time (2012, 2013, and 2014) and 12 months of post disinfection time (2015). The dependent variables are hospital acquired and nursing home acquired infection rates for the urinary tract, respiratory tract, and skin. Enteric infections occurred at such a low frequency inferential analyses could not be performed. Univariate analyses of variance (ANOVAs) were initially examined to determine if there were significant differences in rates of urinary, respiratory, and skin and enteric infections between the three pre and one post ultraviolet irradiation study periods. The effect of the ultraviolet disinfection was computed using ANOVA with an a priori contrast comparing the ratio of hospital acquired to nursing home acquired infections from pre to posttest. If the hospital acquired rate increased and the nosocomial rate decreased or stayed the same the ratio increased. If the hospital acquired rate decreased and the nosocomial rate stayed the same or decreased the ratio decreased.
Rates of infection-related hospitalization were compared from pre to posttest using Chi Square. Hospitalization rates per month were examined relative to the monthly census during that time period.
