Contamination of X-Ray Cassettes with MRSA during Portable X-Ray Examination
Christopher W.K. LAI*1, Polly H.M. LEUNG1 and Helen K. W. LAW1
1Department of Health Technology and Informatics, The Hong Kong Polytechnic University, Hung Hom, HKSAR, China
Aim: To perform surveillance cultures of methicillin-resistant Staphylococcus aureus, methicillin-susceptible Staphylococcus
Methods: The patient-contact and non-patient-contact surfaces of 80 X-ray cassettes used after portable X-ray examination from two hospitals were swabbed. Suspected methicillin-resistant and methicillin- susceptible staphylococcal colonies were analyzed by SA SelectTM and MRSA SelectTM medium plates. The overall bacteria count was analyzed by nutrient agar medium plates.
Findings: A total of 240 swab samples collected from the patient-contact and non-patient-contact surfaces of 80 X-ray cassettes were collected during four hospital visits. We found three X-ray cassettes (3.8%) had methicillin-resistant Staphylococcus aureus colonies isolated, and two other X-ray cassettes (2.5%) had methicillin-susceptible Staphylococcus aureus colonies isolated on their surface after cultured for 24 hours. Moreover, we found 63 cassettes (78.8%) had different degrees of bacteria colonies isolated on nutrient agar, and three swab samples even yielded more than 300 bacterial colonies.
Conclusions: In the hospital environment, the surface of x-ray cassettes may be contaminated by MRSA during portable X-ray examination. Further improvement in the routine preventive measures against pathogen contamination is therefore suggested.
Staphylococcus aureus is a potential pathogen commonly found on our skin and the respiratory tract. The asymptomatic infected patient can transmit these pathogens by direct and/or indirect contact to others and to the environment . In particular, methicillin-resistant Staphylococcus aureus (MRSA) is regarded as one of the highly pathogenic bacteria which could lead to severe infections like pneumonia and infective endocarditis . MRSA can be transmitted from infected patients to inanimate surfaces by contact, survive on the inanimate surfaces for longer than a month , and contaminate the hands and uniforms of healthcare personnel during health care procedures . Therefore, MRSA is a potential threat for the nosocomial infection that poses burden for the management of hospitals.
Pathogen contamination of radiographic equipment and accessories are unavoidable. The radiology department receives a large number of patients from hospital wards and outpatient clinics every day. The pathogens are brought to the department by patients and due to the intimate contact between the surface of the radiographic equipment and staff with the patient, there is a high risk of disease transmission from patient-to-staff and from patient-to-patient through direct and/or indirect contacts within the crowded space of the radiological examination room. The high patient traffic in the radiology department also increases the opportunities for the spread of pathogens, including the spread of MRSA among patients and radiology staff.
Portable X-ray examination is essential to monitor the health status of the critically ill patients in wards. Fox and Harvey (2008)  found that the patient-contact surfaces of X-ray cassettes used “within” the X-ray department were contaminated with bacteria, and the most common bacterium found in their study was Staphylococcus aureus . To the best of author's knowledge, similar study on portable X-ray examination in the hospital environment has not been studied. Therefore, the aim of the present study was to perform surveillance cultures of MRSA, methicillin-susceptible Staphylococcus aureus (MSSA) and bacteria on both patient-contact and non-patient-contact surfaces of X-ray cassette during portable X-ray examination.
Materials and Methods
All swab samples were then inoculated and cultured on nutrient agar medium plate, SA SelectTM medium plate and MRSA SelectTM medium plate (Bio-Rad Laboratories, Inc., Hercules, California, USA) at 37 oC for 24 hr. The number of colony forming units formed on the nutrient agar plates, SA SelectTM medium plates, and MRSA SelectTM medium plates represents the number of bacteria, MSSA, and MRSA colonies respectively.
We also observed the procedure of before, during and after the portable X-ray examination in the two hospitals, and noted
We have performed a random check on eight of the total 80 X-ray cassettes for the presence of any bacteria before the starts of the portable X-ray examination session, and the result indicated that the sampled X-ray cassettes were free from any bacteria contamination before use. After the end of the portable X-ray examination, we have collected a total of 240 swab samples from 80 X-ray cassettes. The number of colony forming units isolated on nutrient agar medium plates, SA SelectTM medium plates, MRSA SelectTM medium plates from this study were presented in Table I.
Table I. Bacteria Surveillance Test. Surveillance cultures of bacteria, MSSA and MRSA on surfaces of X-ray cassettes.
The overall bacteria contamination rate in Hospital A and Hospital B was 57.5% and 100% respectively. Hospital A disinfects
Table II. The Infection Control Measures Implemented in Hospital A and B. A summary of various infection control measures that implemented (✓) or not implemented (✗) in Hospital A and B.
Dancer (2004)  study suggested a standard to evaluate the hygiene of environmental objects. If MRSA and MSSA colony count was smaller than 1 colony per 1cm2(or 100 per 100cm2) and the total aerobic colony count was below 5 per cm2 (or 500 per 100cm2), the surface of an object can be regarded as hygienic . In our present study, only three X-ray cassettes had isolated with MRSA, and the largest MRSA colony count was only 3 per 100cm2. Similarly, the total microbial colony count on X-ray cassettes was generally little, except two swab samples had the colony count exceeding 300 per 100 cm2, and another one exceeding 500 per cm2.
MRSA on the X-ray cassette increases the risk of its spread in hospital setting, since it could survive on nearly all surfaces, including inanimate ones  and from the environmental surfaces to the radiology and nursing staff . During portable X-ray examination, the X-ray cassette had made contact with the environmental objects. We observed the X-ray cassettes were being placed on tables, on the ground or even with the body contact of the radiation technologist during the portable X-ray examination. All these acts may directly or indirectly contaminate the X-ray cassettes with pathogens, especially if the environmental objects had already contaminated by pathogen-carrying patients [4,11]. Nevertheless, the MRSA contamination rate in our study was only 3.75%, which was far lower than a previous study reported by Kim et. al.  (16.2%) The two hospitals in the present study had adopted different infection control measures during portable X-ray examination.
The radiation technologist in Hospital A wore gloves during portable X-ray examination. Additional preventive measures, including cleansing the X-ray cassettes, wearing surgical mask and changing gloves in between handling of patients, were performed in this hospital in order to further reduce the chance of pathogen contamination when handling with very ill patients.In Hospital B, the radiation technologist had used a plastic bag cover to protect X-ray cassette before and during examination. However, all these measures taken by radiation technologist cannot totally eliminate bacteria contamination.
The results of the present study were agreed with a systematic review of healthcare workers’ knowledge about MRSA and/or frequency of cleaning practices, in which they concluded that the cleaning practices to ensure minimization of MRSA contamination of equipment by healthcare workers were generally insufficient and non-appropriate . Indeed, neither contact precautions nor cleaning could get rid of all pathogens in the hospital setting [6,7]. With this in mind, it is a no wonder that radiographic equipment and accessories are at a high risk of being contaminated by MRSA, and potentially becomes microbial-contaminated fomites for transmission of MRSA.
A recent article has updated the National evidence-based guidelines for preventing healthcare-associated infections in NHS hospitals in England . This updated guideline emphasis the contamination prevention measures should be based on reliable evidence of efficacy, and combined with quality improvement methods. Concerning to the recommendation of these guidelines, the radiographic equipment and accessories should be cleaned and decontaminated after use with proper cleaning agents recommended by the manufacturer. Most significantly, all healthcare workers should be educated about the
Cite this article: Christopher W.K. Contamination of X-Ray Cassettes with MRSA During Portable X-Ray Examination. J J Microbiol Pathol. 2014, 1(1): 007.