Healthcare-Associated Infections Related to Procedures Performed in Radiology
Bruce S. Ribner
The radiology department has traditionally been considered a low-risk environment for healthcare-associated infections. However, major advances in the field of radiology over the past few decades, with the introduction of isotope scanning, ultrasound, computed tomography, magnetic resonance imaging, and the development of interventional radiology, have increased the potential for the transmission of infectious pathogens to both patients and healthcare workers. Unfortunately, an appreciation for the occurrence of healthcare-associated infections associated with these radiologic procedures has not kept pace with this technology (1,2). Few radiology texts address healthcare-associated infections associated with radiologic procedures. In addition, most invasive radiologic procedures introduced over the past few decades have not been prospectively analyzed for measures that could decrease the occurrence of healthcare-associated infections resulting from them. This is due, in part, to the rather limited time during which the radiologist interacts with the patient, and the resulting difficulty in achieving the long-term follow-up required to identify healthcare-associated infections.
This chapter summarizes the infectious complications associated with radiologic procedures and the infection control practices that might decrease the occurrence of these infections. As conclusive data regarding the prevention of healthcare-associated infections are lacking for many of these procedures, reliance is placed largely on related procedures performed in other specialties of medicine in which interventions that reduce the healthcareassociated transmission of infectious pathogens have been identified.
INFECTION CONTROL POLICY
The radiology suite experiences a steady stream of a wide variety of patients each day. Patients referred from the ambulatory care and emergency areas are intermixed with inpatients requiring diagnostic procedures. All of these patients can contaminate the environment of the radiology service with infectious pathogens. Chin supports and chest racks used in obtaining chest radiographs (3), radiography tables (3), radiographic film markers (4), barium enema equipment (5), x-ray tubes (6), and x-ray film and developing solutions (7) may all become contaminated with multiple microorganisms from patients. In addition, the ease with which Clostridium difficile contaminates the environment of the patient colonized with this microorganism (8) makes it likely that contamination of the radiology area with C. difficile occurs as well. This environmental contamination may result in the subsequent spread of pathogenic microorganisms from these objects to other patients. In addition to fomite transmission, potential pathogens may be spread to patients visiting the radiology area via the airborne route. Hopkins et al. (9) traced an outbreak of invasive aspergillosis in their hospital due to construction activity in the radiology suite. Patients visiting the radiology suite for diagnostic procedures were infected when there was inadequate containment of aspergillus spores generated during renovation. Similarly, investigations of hospital outbreaks of multidrug-resistant tuberculosis have revealed that most cases were acquired within the facilities via the airborne route. A major factor in most of these outbreaks was a delay in initiating the isolation of patients infected with pulmonary tuberculosis (10). Many of these patients had made multiple visits to the radiology department, with no precautions taken to prevent the transmission of respiratory pathogens, making it likely that some transmission occurred within the radiology department.
Given the large numbers of both diagnosed and undiagnosed infected patients presenting to the radiology department, and the potential for these patients to contaminate both objects and the air with pathogenic microorganisms, the foundation of any program for the prevention of healthcare-associated infections in the radiology department must begin by establishing good infection control policies. Among other issues, these policies must address the effective disinfection of environmental surfaces likely to act as fomites. The cleaning of these surfaces must be performed with an Environmental Protection Agency (EPA)-registered germicide (see also Chapter 80) between all patients, with more rigorous cleaning protocols at periodic intervals (11) (see also Chapter 71). A material that can be either discarded or easily disinfected between patients should cover surfaces that may be difficult to disinfect, such as switches and control panels. Policies should ensure that all disposable items are discarded after a single patient use, as such items are not designed for reprocessing and reuse on multiple patients (11). Attention must also be given to the appropriate cleaning and disinfection of all reusable
equipment, with the level of disinfection determined by the intended use of the item (see also Chapter 80). Items that enter tissues or vascular spaces require sterilization. Items that contact mucous membranes or nonintact skin require high-level disinfection. Items that contact intact skin require only low-level disinfection.
equipment, with the level of disinfection determined by the intended use of the item (see also Chapter 80). Items that enter tissues or vascular spaces require sterilization. Items that contact mucous membranes or nonintact skin require high-level disinfection. Items that contact intact skin require only low-level disinfection.
The radiology department must also establish good communication with the clinical areas referring patients to the department so as to identify patients who may require Transmission-Based Precautions. Patients requiring Transmission-Based Precautions must have those precautions continued in the radiology department. When possible, patients on Transmission-Based Precautions should undergo their procedures late in the day when traffic in the department is light and more attention can be given to environmental cleaning. These patients should also spend the minimum time possible in the radiology department so as to limit the potential exposure of susceptible patients and staff.
Due to concern about the healthcare-associated transmission of tuberculosis in the radiology suite (see also Chapter 38), the Centers for Disease Control and Prevention (CDC) has published specific recommendations for precautions to be followed in radiology departments (10). Patients with known or suspected tuberculosis should wear a properly fitted surgical mask when in the department. When possible, an area in the department should be specially ventilated for Airborne Infection Isolation Precautions. This requires a net negative air pressure in relation to surrounding areas, sufficient air changes to remove droplet nuclei between patients, and either direct exhausting of all air to the outside (preferred) or filtration of air through high-efficiency particulate air (HEPA) filters before it is recirculated. In facilities with a high incidence of tuberculosis, ventilation in waiting areas should also be designed and maintained to reduce the risk of tuberculosis transmission. This should include provisions for direct exhausting of all air to the outside (preferred) or HEPA filtration of all air before it is recirculated. A goal of 12 to 15 air changes per hour for such waiting areas has been established (12,13).
STANDARD PRECAUTIONS
The infection control measures discussed above protect employees and patients from the transmission of most potential pathogens. However, attention to the transmission of blood-borne pathogens in the workplace increased in the 1980s. Hepatitis B virus (HBV) and the human immunodeficiency virus (HIV) are the blood-borne pathogens that have attracted the most attention from healthcare workers and regulatory agencies (14).
Personnel working in radiology departments historically have not been considered a group at high risk for infection with blood-borne pathogens (14, 15, 16 and 17). However, radiology personnel are increasingly performing procedures that can result in exposure to blood and other potentially infectious materials (materials epidemiologically linked with the transmission of blood-borne pathogens) (18). Because a high percentage of patients infected with HBV (19) or HIV (20) are unidentified during their encounter with the healthcare system, it is essential that all patients be approached as though they are infected with blood-borne pathogens. This concept of using Universal Precautions (see also Chapter 89) for blood and other potentially infectious materials of all patients was first suggested by the CDC in 1987 (21). These precautions were subsequently mandated by the Occupational Safety and Health Administration for all healthcare workers (14). In 1996, the CDC recommended replacement of Universal Precautions with Standard Precautions, a change aimed at focusing more attention on pathogens that are not primarily blood-borne (22). Reports have detailed how these precautions can be applied to the radiology department (18,22,23, 24 and 25). In general, these recommendations mirror those for other areas of the hospital in which similar procedures are performed (Table 68-1).
SPECIFIC PROCEDURES
Radiographic Studies of the Gastrointestinal Tract
The spread of enteric pathogens during radiologic procedures of the gastrointestinal tract has been a matter of concern for a number of years. Meyers (5) and Steinbach et al. (26) demonstrated retrograde contamination
of the apparatus used for administering barium during the performance of barium enemas. This equipment became heavily contaminated with fecal contents by the end of the procedure. Hervey (27) reported an outbreak of typhoid fever traced to an apparatus that resembles the equipment used to administer barium during a barium enema. In his investigation, as in those by Meyers and by Steinbach et al., it was noted that fecal contents could contaminate the apparatus and its tubing via retrograde flow during the procedure. Although the apparatus was cleaned between patients, sufficient microorganisms remained in the apparatus to infect patients on whom it was subsequently used. Similarly, Meyers and Richards (28) were able to demonstrate that six of seven patients who underwent barium enemas after contamination of the bag contents with poliovirus became infected with the polio virus, as documented by rises in serum neutralization antibodies to the virus. In a related report, 36 cases of amebiasis were traced to a contaminated colonic irrigation machine in an outpatient chiropractic clinic (29). Although the irrigation equipment was cleaned after each patient use, cultures of the machine immediately after cleaning revealed heavy contamination with fecal coliforms. The ease with which C. difficile contaminates the environment of colonized and infected patients (8) makes it likely that this bacterium is also present where gastrointestinal procedures are performed.
of the apparatus used for administering barium during the performance of barium enemas. This equipment became heavily contaminated with fecal contents by the end of the procedure. Hervey (27) reported an outbreak of typhoid fever traced to an apparatus that resembles the equipment used to administer barium during a barium enema. In his investigation, as in those by Meyers and by Steinbach et al., it was noted that fecal contents could contaminate the apparatus and its tubing via retrograde flow during the procedure. Although the apparatus was cleaned between patients, sufficient microorganisms remained in the apparatus to infect patients on whom it was subsequently used. Similarly, Meyers and Richards (28) were able to demonstrate that six of seven patients who underwent barium enemas after contamination of the bag contents with poliovirus became infected with the polio virus, as documented by rises in serum neutralization antibodies to the virus. In a related report, 36 cases of amebiasis were traced to a contaminated colonic irrigation machine in an outpatient chiropractic clinic (29). Although the irrigation equipment was cleaned after each patient use, cultures of the machine immediately after cleaning revealed heavy contamination with fecal coliforms. The ease with which C. difficile contaminates the environment of colonized and infected patients (8) makes it likely that this bacterium is also present where gastrointestinal procedures are performed.
TABLE 68-1 Standard Precautions as Applied to Radiology | ||
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Given this potential for the transmission of enteric pathogens, all equipment used in barium enema procedures either must be subjected to high-level disinfection or must be disposable. In fact, disposable kits have replaced reusable equipment in most facilities (30,31).
Several investigators have documented bacteremia associated with radiologic studies of the gastrointestinal tract. In two large studies, 11% (32) and 23% (33) of patients undergoing barium enemas had bacteremia. In both reports, the bacteremia could be detected within 1 minute of the start of the procedure. This bacteremia was transient and could be documented only for 30 minutes. Radiologic findings and colonic pathology did not influence the likelihood of the occurrence of bacteremia. Bacteremia was most likely to occur during the maximal distention of the colon. In evaluating the patients in these studies, no adverse effects of the bacteremia could be documented. However, one episode of Clostridium perfringens sepsis has been reported in a patient with acute leukemia who underwent a barium enema (34). Although the transient bacteremia associated with the barium enema is unlikely to adversely affect most patients, bacterial endocarditis after a barium enema has been reported in one patient (35). This has, in turn, raised the question of antibiotic prophylaxis for the prevention of infective endocarditis (36,37). However, barium enemas have not been found to be a risk factor in studies evaluating the epidemiology of bacterial endocarditis. Although a definitive answer is probably not possible, the current consensus is to avoid the use of prophylactic antibiotics for patients undergoing barium enemas (34).
Ultrasound Procedures in Radiology
Ultrasonography has become an increasingly popular mode of evaluating a wide range of tissues. It is estimated that the average ultrasound machine may be used on as many as 30 patients a day, giving this equipment the potential to serve as an important fomite for the transmission of pathogens between patients (38). Although many of these procedures restrict the ultrasound probe to contact with intact skin, probes are also being utilized for procedures in which they come into contact with mucous membranes and normally sterile tissues, occasionally in the operating room. Several studies have documented heavy contamination of the ultrasound probe, especially after contact with a mucous membrane (38, 39 and 40).
The standard manufacturer’s recommendation for disinfection of the ultrasound probe is to soak the probe in a dilute sodium hypochlorite solution or an EPA-registered germicide for the time specified by the germicide’s manufacturer, frequently 20 minutes. Unfortunately, the multiple procedures scheduled for these probes frequently preclude such long soak times. In addition, the probes may be damaged by total immersion in these solutions due to leakage around the seals or deterioration of the acoustic lens or rubber seals (38,41). In practice, routine cleaning of the probe followed by low-level disinfection with an alcohol wipe seems appropriate when procedures involve contact only with intact skin. For procedures where the probe comes into contact with mucous membranes or nonintact skin, thorough cleaning followed by high-level disinfection with an EPA-registered germicide is recommended (11,42). Because of the difficulty in achieving high-level disinfection, it is recommended that a new sheath, such as a condom, cover probes that will be in contact with mucous membranes or sterile tissues for each such procedure (11,42). In general, condoms have been shown to be less prone to leakage than commercial probe covers and have a sixfold enhanced acceptable quality level when compared to standard examination gloves.
Endoscopic Procedures in Radiology
Other subspecialists such as gastroenterologists, pulmonologists, and surgeons perform endoscopic procedures much more frequently than they are performed by radiologists. Often, endoscopy is not performed in the radiology suite but rather in patient care areas, in the operating room, or in other dedicated areas such as laboratories within the hospital or ambulatory center. To the extent that endoscopy is performed in areas outside of radiology, general infection control policies similar to those recommended for the radiology suite need to be implemented.
Endoscopic procedures of the pulmonary tract (43, 44 and 45), upper gastrointestinal tract (35,45, 46 and 47), lower gastrointestinal tract (35,45), and biliary tract (45,48) have all been associated with healthcare-associated bacteremia and infections. Salmonella species and Pseudomonas aeruginosa are the most common pathogens isolated in infections after gastrointestinal endoscopy, whereas Mycobacterium tuberculosis, nontuberculous mycobacteria, and P. aeruginosa are the most common isolates in infections after bronchoscopy (45). In general, P. aeruginosa and nontuberculous mycobacteria tend to come from environmental contamination of the equipment, whereas Salmonella and M. tuberculosis originate in patients previously studied with the endoscopes.
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