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Original Research |
1 Department of Clinical Radiology, University of Muenster,
Albert-Schweitzer-Strasse 33, 48149 Muenster, Germany.
2 Institute of Hygiene, University of Muenster, Germany.
Received March 7, 2008;
accepted after revision June 27, 2008.
Address correspondence to B. Buerke
(buerkeb{at}uni-muenster.de).
Abstract
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MATERIALS AND METHODS. Microbiologic contamination of CT injector syringes over multiple uses for several injections was investigated in an experimental setup simulating the clinical setting. Each refill and injection operation was performed by the same technician, who processed a contrast agent for administration in a neighboring room as in clinical CT routine. Multiple administrations of nutritive medium and a chaser bolus were performed with the injection syringes. Simultaneously with each syringe replacement and filling operation, the filling and injection operation was simulated with a separate injection system under normal clinical conditions. Hygienic conditions in the CT department also were evaluated. For microbiologic analysis of devices and of palms of staff, imprints were obtained during clinical routine at the beginning of the study and at follow-up. Throughout the study, the staff participated in continuing education on hygienic behavior, such as hand disinfection and wearing of sterile gloves. In addition, clinical injector syringes were checked for microbiologic contamination.
RESULTS. In the experimental setup, the first four samples of each simulation experiment were sterile, and the subsequent probes were found to be contaminated with typical dermal bacteria, such as staphylococci. In the CT department, contamination with skin and oral flora was found on surfaces of devices and on palms. No imprint of surfaces or palms was contaminated with nosocomial or fecal pathogens.
CONCLUSION. Because even optimization of environments does not prevent contamination of syringes, multiple uses of syringes for more than one patient should be prohibited owing to the risk of septic complications.
Keywords: automatic injector • contrast agent • CT • hygiene • microbiologic contamination
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The need for increasing capacity in radiology departments forces the staff in CT units to obtain scans as efficiently as possible to optimize workflow. Multiple use of the syringes of automatic injectors for more than one patient may be one option for shortening preparation time, that is, the time of injector assembly and refill of syringes, to improve the efficiency of workflow. In principle, owing to the typical capacity of injection syringes (250 mL), consecutive injections to more than one patient are possible after one filling process. Only equipment that directly contacts patients, that is, the tube and connector, has to be removed after each examination and exchanged before the next CT examination.
Frequent handling of automatic injectors while the system is assembled and refilled increases the risk of bacterial contamination of injection tubes and syringes [1]. Several studies [2–7] have been focused on the effect of hand disinfection on hygienic conditions in medical departments such as the ICU. There is little information, however, on the risk of bacterial contamination of injection systems by the medical and technical staff during single or multiple uses of syringes under routine clinical conditions [1]. Nevertheless, the risk of bacterial contamination of iodinated and gadolinium-based contrast agents due to improper storage of contrast agents and multiple dosages from the same vial is well known [6–11]. In addition, warming of contrast and saline syringes to 37°C by the injector to reduce viscosity and facilitate administration provides optimal conditions for organism reproduction. This study was conducted to investigate in an experimental simulation model and in clinical routine the risk of microbiologic contamination of the contrast agent and syringes of MDCT injectors by medical and technical staff.
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Experimental Study: Bacterial Contamination of Syringes
Normal hygienic conditions—In the experimental study,
multiple uses of injection syringes to administer tryptic soy broth instead of
a contrast agent with an automatic CT injection system and of the
corresponding disposable tubes were simulated. The injector (Injectron CT,
Medtron) was located in a separate CT room next to the suite in which clinical
routine CT examinations were performed.
The CT injection system consisted of two injection syringes, one for the contrast agent and one for saline solution, which were connected by a T-shaped connector. A one-way valve was placed in the contrast agent branch of the injection tube to avoid invasion of saline solution into the contrast agent syringes. Bacterial filters were not integrated into the lines. The injection tube was adapted to the patient tube, which was positioned during venous catheterization (Fig. 1). Although the injection syringes and injection tube were used multiple times, the patient tube was used once.
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Intensive hygienic prevention—In the second part of the experimental study, the effect of intensive hygienic teaching and strict hygienic instruction on multiple uses of contrast and saline syringes was investigated. The simulation experiment of multiple uses was repeated after intensive teaching of CT department staff by infection control personnel at our institution. In addition to general hygienic regulations, strict instructions were given to the staff to perform proper hand disinfection with a standard alcohol-based disinfectant solution before every injector assembly, as recommended by the national guidelines issued by the federal institute responsible for disease control and prevention [8]. In addition, the technical staff was instructed to wear sterile gloves during connection of each patient tube to the injection system and injector assembly. Each simulation experiment was performed over 8 consecutive days to achieve a valid database of 17 samples per day (n = 136). Syringes were replaced and changed after the eighth or ninth filling and injection process.
Clinical Study: Bacterial Contamination of Palms and Surfaces
In addition to the experimental study, a clinical investigation was
performed to evaluate the bacterial contamination of the palms of staff and of
surfaces in the CT unit. Imprints of the palms of technical and medical staff,
who were not given notice of the testing, and of surfaces were obtained by the
infection control personnel at our institution. In the CT unit, imprints were
obtained from three PC keyboards, the desktop of the operation panel, the
telephone receiver, the CT gantry, the inner wall of the CT tunnel, the
automatic injectors (button panel and syringes), and the support pillows.
Imprints of the palm and sides of the hands were obtained with agar plates
(RODAC, BD Diagnostic Systems) during routine work
[9]. The surface imprints were
obtained after at least 4 hours of work. The imprint analysis was performed
twice (n = 44 each trial).
Microbiologic surveillance cultures were obtained at different time intervals for analysis of the effectiveness of hygienic teaching of the technical and medical staffs. On the basis of recommendations from a previous study [1], the technical and medical staffs were given regular instruction on proper hygienic behavior every 6 months. The medical and technical staffs were urged to perform sufficient hand disinfection before and after each contact with patients, for example, in patient reception and positioning [8]. According to standard procedure, cleaning personnel intensively cleaned the surfaces of the CT scanner and the CT room once per day with antiseptic detergents. During operation, the technical CT staff is responsible for continuous cleaning.
Data Analysis
Microbiologic analysis of bacterial contamination of palms, surfaces,
and syringes—Analysis of bacterial contamination was performed with
standard microbiologic methods. For the simulation experiment, 140 mL of broth
and 50 mL of 0.9% sodium chloride were collected in sterile vials, which were
placed in an incubator. Before incubation, air filters were connected to the
vials under sterile conditions on a clean bench to allow aerobic bacterial
growth within the vials. After 7 days of incubation, the vials were opened
under sterile conditions, and 100 µL of the broth was streaked out onto
Columbia blood agar plates. After 48 hours of incubation, the plates were
visually inspected. If bacterial growth was detected, the colonies were
differentiated by use of standard microbiologic techniques
[9]. The ana lysis of bacterial
contamination of palms and surfaces was performed with RODAC agar plates with
Columbia blood agar. The RODAC plates were lightly pressed on the investigated
surfaces and palms for 3–5 seconds. After 48 hours of incubation, the
colonies were counted, and the bacteria were differentiated. All incubation
steps were performed at 37°C under aerobic conditions
[9].
Data interpretation—The results of microbiologic analysis are evaluated in thresholds and interpreted as clinical observations. Contrast agent and syringes were designated for parenteral administration. Every microbiologic contamination was evaluated as contaminated. For further evaluation of contamination, we determined after which injection process the syringes were contaminated during multiple uses. The average (mean ± SD number of injections) initial contamination was statistically analyzed for the normal hygienic conditions and intensive hygienic prevention parts of the experiment.
Bacterial contamination of surfaces and palms was counted in colony-forming units (CFU). Thresholds in the literature [9] were used to designate fewer than 40 CFU as acceptable and 40 CFU or more as contaminated. Each surface and palm was considered separately. It therefore was not possible to perform statistical analysis by averaging different surfaces and palms. The contamination of surfaces and palms was an overview of the hygienic conditions in which the simulation experiments were performed.
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Bacterial contamination of syringes: normal hygienic conditions—Microbiologic analysis of the collections of nutritive medium used instead of a contrast agent in the experimental setup revealed contamination with skin and oral flora, such as coagulase-negative staphylococci and nonhemolytic streptococci, at the earliest after the fourth probe of each trial (4 ± 0.5 injections) under normal hygienic conditions. No collected medium was contaminated with nosocomial pathogens or with fecal bacterial flora, such as Staphylococcus aureus and Pseudomonas species (Table 1).
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Bacterial contamination of syringes: intensive hygienic prevention—Microbiologic analysis of syringes used multiple times revealed bacterial contamination even under intensified hygienic prevention, that is, hand disinfection before every contact with the injection system and wearing of sterile gloves during injector assembly and connection of tubes. Samples from the seventh and eighth injections (7.5 ± 0.5) in each half of the experimental study were not sterile and showed contamination with Micrococcus species (Table 1).
Clinical Study: Bacterial Contamination of Palms and Surfaces
Microbiologic analysis of bacterial contamination on imprints (n =
88) of the palms of medical and technical staff and of surfaces in the CT unit
obtained during clinical routine revealed contamination with typical skin
flora, such as coagulase-negative staphylococci, and environmental bacteria,
such as Bacillus species (Table
2). No imprints of surfaces or hands were contaminated with
nosocomial pathogens or fecal flora. The imprints obtained during routine work
without previous direct disinfection showed at most 26 CFU on surfaces and at
most 39 CFU on hands, indicating the hygienic condition of surfaces and palms.
No contamination of palms and surfaces with fecal organisms indicating heavy
lack of compliance with hygienic regulations was detected.
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Because of restrictions by national regulatory authorities, such as the Federal Institute for Drugs and Medical Devices in Germany and the Food and Drug Administration in the United States, and instructions for use issued by manufacturers, the syringes, disposable tubes, and connectors of CT injectors are regularly approved for a single use only. There is only a small amount of data on the risk of bacterial or other microbiologic contamination of contrast agents caused by handling of contrast agent vials [7–13]. To our knowledge, results of only one preliminary study [1] on the hygienic aspects of automatic CT injection systems have been published.
We hypothesized that adequate hygienic conditions reduce the risk of bacterial contamination during handling of the injection syringes of automatic CT injectors. Therefore, we simulated multiple uses of syringes under regular hygienic conditions and under intensive hygienic prevention during injector assembly. Injection syringes were sterile after the first injection in the experimental setting. Microbiologic analysis of the simulation experiment revealed bacterial contamination of syringes after the fourth injection under normal hygienic conditions and after the seventh injection with intensive hygienic prevention. Thus this study showed that bacterial contamination of syringes during multiple uses can be postponed with regular hygienic behavior.
However, even intensive hygienic prevention with additional hand disinfection before each contact with the CT injection system and wearing of sterile gloves during injector assembly and connection of tubes did not completely prevent bacterial contamination of CT injection syringes. The results of this study confirm that injection syringes remain sterile during a single use; after the first injection syringes were not contaminated under either normal or intensive hygiene. Nevertheless, even with intensified hygienic precautions, multiple uses of syringes for more than one injection for contrast-enhanced CT should be prohibited.
The effect of the documented contamination of syringes and tubes on patients, especially those with immune deficiencies, can only be presumed. In accordance with published data [14, 15] on the hygienic aspects of venous shunts and central venous catheters, that microbiologic contamination of syringes and tubes poses an infection hazard to patients cannot be excluded. To our knowledge, however, there are no sufficient or statistically valid data on the effects of pathogens parenterally acquired in contrast administration processes. Ethical considerations precluded performance of this study with human subjects rather than in an experimental setting.
According to the results of previous studies [1–6, 16–18] on hygienic conditions in CT and MRI departments, intensive hand disinfection and periodic teaching of hygienic principles for technical and medical staff are required to prevent bacterial contamination of injection syringes and the risk of patient impairment. The results of our study show that hygienic conditions in a CT department can be continuously achieved for periods of several months if technical and medical staff are given regular strict instruction on standardized hygienic practices. In this regard, regular teaching of the technical and medical staff is recommended for detection and correction of potential deviations in hygienic procedures as the result of inattentiveness in clinical routine and staff fluctuation. We believe the effectiveness of hygienic procedures should be validated with microbiologic surveillance cultures twice a year. Further clinical trials are needed to determine the effect of modern innovations in the construction of automatic injectors (e.g., bacterial filters, special one-way valves) on hygienic conditions; multiple uses of syringes should be included in those trials.
In conclusion, the use of injection syringes for more than one patient should be prohibited because of the risk of infection due to contamination of the syringes and tubes. Only a single use of an injection syringe for one patient provides hygienic conditions that ensure the sterility of a CT injection system. In addition, regular unannounced evaluations of the hygiene of the CT department are recommended as part of a quality assurance program.
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