Instructions: Spend 10 minutes reviewing the case below and considering the questions that follow. Case Study 4: Xenon UV decontamination
Cooley Dickinson Hospital is a 140-bed acute care community hospital in western Massachusetts with mostly single-bed rooms. Like many hospitals, there was concern that contamination of patient rooms from previous occupants is associated with C. difficile infections. In 2011 the hospital began using two portable pulsed xenon ultraviolet (PPX-UV) devices in an attempt to reduce C. difficile incidence. 72 Rooms and bathrooms were terminally cleaned as usual with a hospital-grade disinfectant product in most rooms and a chlorine-based product in C, difficile rooms. This was followed by the use of PPX-UV, for three 7-minute exposures (once in the bathroom and then in 2 locations in the main patient room). The overall room turn-over time was extended by approximately 15 minutes over a standard terminal cleaning because cleaning could continue in the main room during PPX-UV treatment of the bathroom. PPX-UV devices were also used in the operating suites (nights), emergency department (early mornings), and other clinical areas as available. The PPX-UV device contains a xenon flash lamp that emits a broad spectrum of light covering the germicidal, or ultraviolet-C spectrum as well as the visible light spectrum. The device weighs approximately 150 pounds. The PPX-UV system produces a pulsed flash at a frequency of 1.5 Hz and a duration of less than 360 ms. The device is operated remotely in the hallway just outside the patient room and includes safety features such as motion sensors, which turn off the device if the door is opened. Rates of C. difficile infections at Cooley Dickinson had been stable at an average of 9.22 per 10,000 patient-days for the years 2008 to 2010. In 2011, the year after the PPX-UV devices were used, the rate fell to 4.45 (53% reduction; P = 0.01). Of the 15 patients who were diagnosed with HA-CDI in 2011, 11 (73%) were placed in rooms that had not been treated with the PPX-UV device prior to occupation. Overall, 56% of discharged rooms received the UV light treatment. One reason some rooms were not treated was the simultaneous discharge of a number of patients and the limited number of devices. In addition, whereas most of the hospital’s rooms are single occupancy, occasionally 2-bed rooms with 1 patient remaining could not be fully treated, although often the bathroom was treated. The authors concluded that the dramatic reduction in infection rates make the use of PPX-UV well worth investigating further in larger studies.
1. Thinking about your own institution how effective do you think efforts are to prevent C. difficile infections? In what ways could those efforts be improved?
2. If you have had experience with PPX-UV devices, do you think these are a feasible technique for wider use? Why or why not?
3. What kinds of barriers to wider use of PPX-UV devices might need to be overcome?
While testing accuracy and speed have improved in the last 10 years, there is currently no consensus onthe best testing method. It is helpful for clinicians to understand the strengths and limitations of the testing methods when interpreting test results. The testing methods have varying sensitivities and specificities, due to each test’s detection ability and the tests’ different detection targets. Each class of test targets one of the following: C. difficile toxin, genes that produce toxin, or identification of toxigenic C. difficile in the stool. Detection of genes that produce toxins and toxigenic C. difficile indicates a patient may be colonized or infected with C. difficile . Detection of C. difficile toxin indicates infection. Each of the targets can indicate different stages in the progression of the disease. Some patients may remain colonized and acquire protection from disease while others progress to the disease. Some with symptoms may be treated and become asymptomatic carriers. The criteria for whom to test for CDI such as the number and frequency of diarrheal stools that should trigger testing have decreased in the last few decades. Whole genome sequencing and molecular typing indicate that most CDI is acquired from sources other than symptomatic cases.
Asymptomatic colonized patients do not shed as many C. difficile spores as CDI patients; however, they still contaminate the environment. Evidence supports identifying asymptomatic colonized C. difficile patients for the purpose of isolation and contact precautions. In the last decade, the most commonly used standalone test method has shifted from enzyme immunoassays to tests that detect DNA. Known as nucleic acid amplification testing, or NAAT, these tests generally have better detection abilities than enzyme immunoassays. A shift to more rapid and accurate testing results in less use of unnecessary CDI-targeted antimicrobials and a decrease in laboratory testing volume. NAAT detects toxigenic C. difficile genes, not the damaging toxins, and may identify asymptomatic carriers as well as those with C. difficile disease; also, there is debate about whether the presence of toxigenic C. difficile alone is sufficient to diagnosis CDI. Guidelines therefore suggest that only symptomatic (i.e., those with diarrhea) patients should be tested.
To improve accuracy, combinations of tests are being used. Particularly if laboratories lack clinical input on specimen criteria and accept any unformed stool for testing, it may be most appropriate to use a combination of tests such as a test for organism combined with a relatively sensitive test for toxin in the stool. These combinations test for the toxigenic organism and test for the actual toxin. Testing methods CDI testing methods have different sensitivities and specificities, which impact CDI rates. A number of recent studies have shown that more sensitive molecular testing methods result in higher CDI surveillance rates. The improved sensitivity of molecular tests allows infected and colonized patients to be rapidly and reliably identified but can be “too good” at identifying patients who are colonized but not truly infected with C. difficile . The following testing practices for suspected C. difficile in adults are recommended: • Use patients with unexplained and new- onset ≥3 unformed stools in 24 hours as the preferred target population for testing for CDI
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