Filmcards Used in Radiation Therapy: Are They a Potential Source of Cross-infection?

Industrial radiographic film (exposed to light and then cut into a filmcard) is a tool used by radiation therapists (RTs) in the setup of patients before delivering external beam radiation therapy. At the Tom Baker Cancer Center (TBCC), filmcards are reused throughout the day on multiple patients and multiple body sites; thus the risk of cross-contamination exists. The primary objective of this study was to assess the risk of cross-contamination by determining the potential for bacteria to survive on filmcards, in an effort to reduce the risk of cross-infection.

This control study evaluated the potential of the following to survive on filmcards: coliforms, Pseudomonas, Staphylococcus spp. (specifically S. aureus and methicillin-resistant S. aureus [MRSA]), Enterococcus, and hemolytic streptococcus species. Thirty filmcards used by RTs throughout the day were collected and voluntarily placed in individual collection bags. Thirty control cards (unused filmcards) were also collected. Collection bags were stored at 4°C until cultured. A reference strain of MRSA (38591) was used in the MRSA survival assay, along with methicillin-sensitive S. aureus (MSSA) isolate (pure form). The MRSA survival experiment required eight larger, unused filmcards (four designated as negative controls and four positive control cards) to be cut into 28.5 × 6.5 cm. Microbiological plates were used to identify and select for bacteria. The various selective and differential plates contain growth factors, antimicrobials, and color indicators that can selectively allow some groups of bacteria to grow on the plate while inhibiting other types of bacteria.

This study provides evidence to support that filmcards are a source of cross-contamination. 58% (17/29) of the used filmcards tested positive for pathogenic bacteria, compared to only 20% (6/30) of the control cards (P = 0.003). Staphylococcus aureus bacteria were present on 11/29 (38%) of the used filmcards, compared to 2/30 (6.7%) on the control filmcards (P = 0.005). Other colonies found on the used filmcards included strep bacteria (P = 0.24), entero bacteria (P = 0.24), and skin flora (P = 0.36); and although reported as statistically insignificant, these bacteria were viable and thus hold a level of clinical significance. In addition, this experiment provides evidence that certain bacteria (including MRSA found to survive on filmcards for at least 21 days) were viable on filmcards, but an incidental finding reports that fungi is also able to survive on filmcards.

Filmcards used by RTs can harbor a number of pathogenic bacteria, including MRSA, and are therefore a source of cross-contamination. We recommend that the TBCC external beam radiation treatment program-and any other facilities providing external beam radiation therapy-adopt infection control policies that support discarding filmcards after each use (one-time per patient use) or adopt policies that endorse the elimination of filmcards entirely.