The present study showed that 58.3% of smartphones used by Japanese ICU HCWs were contaminated with bacteria, with 46.4% of the posterior surfaces being involved. CNS and Bacillus species were frequently isolated from these smartphones. No factor was found to be associated with bacterial contamination of the posterior surface.
Previous studies suggested that 10–100% of mobile phones in healthcare settings could be contaminated [11,12,13]. Most of these studies focused on conventional keypad mobile phones. However, a limited number of studies focused on smartphones and suggested that 20.9–99.2% of them in healthcare settings are contaminated [21, 25,26,27,28]. Common microorganisms associated with mobile phone contamination overall included S. aureus, CNS, and Bacillus species [11,12,13], consistent with the present study findings. Although antimicrobial-resistant bacteria were isolated from 1.1% of smartphones, S. aureus, CNS, and Bacillus species can also be causative agents of nosocomial infections, and thus caution regarding smartphone microbial contamination is needed.
In the present study, 46.4% of posterior surfaces of smartphones were contaminated with bacteria, significantly more frequently than touchscreens. The numbers of colonies on touchscreens and posterior surfaces of the smartphones were similar, though small. One previous study screened both surfaces of smartphones, but did not differentiate the surfaces with respect to the prevalence of bacterial contamination . To the best of our knowledge, the present study is the first to focus particularly on the posterior surface of smartphones. In the present study, whereas the touchscreen was contaminated only with Gram-positive bacteria, the posterior surface of the smartphones was contaminated with both Gram-positive and Gram-negative bacteria. The reason for this difference is uncertain.
We considered the following hypotheses for factors related to bacterial contamination of the posterior surfaces of smartphones. First, existing evidence is conflicting regarding whether sex might be a factor associated with smartphone bacterial contamination . Some studies suggested that women store their smartphones in bags, which are associated with high bacterial levels, and heat generated by smartphones and the inside area of bags could support bacterial growth [14, 30]. Thus, female sex was set as a potential factor associated with smartphone bacterial contamination. Second, the posterior surface of smartphones, once covered, or the inside area of the cover is less frequently cleaned by users than the touchscreen, and bacteria are expected to remain on the surface. Third, regular disinfection of smartphones could also reduce or prevent bacterial colonization on smartphone surfaces. However, none of these were found to be associated with bacterial contamination of the posterior surface.
The results of the present study suggested that the posterior surface was more frequently contaminated than the touchscreen, regardless of whether it was covered. Although the posterior surface is not as frequently touched as the touchscreen, it could be a fomite of transmitting bacteria to the healthcare environment once contaminated. Thus, we recommend that the posterior surface of smartphones be cleaned, similar to the touchscreen, in order to avoid cross-contamination of healthcare settings, particularly ICU settings.
In response to the COVID-19 pandemic, the United States Centers for Disease Control and Prevention (CDC) recommends the use of wipeable covers for electronics . However, once contaminated, the area under the cover can harbor pathogenic bacteria that can cause nosocomial infection. Furthermore, if the cover of a smartphone is incidentally removed, bacteria under the cover may move to the healthcare or home environment. The present study suggested that the posterior surfaces, whether or not they were covered, were similarly contaminated with bacteria. Thus, the posterior surfaces need to be cleaned regardless of the presence of a cover.
Whereas the United States CDC recommends that users of electronic devices follow the manufacturer’s instructions for cleaning and disinfecting products, they also recommend the use of alcohol-based wipes or sprays containing at least 70% alcohol to disinfect the touchscreen . Previous studies have demonstrated that a silver-containing antibacterial coating, light-activated antimicrobial agents, antibacterial wipes containing alcohol, chlorhexidine, chlorine dioxide, or quaternary ammonium compounds, and ultraviolet light irradiation successfully decontaminate the touchscreen, some of which also effectively decontaminate the posterior surface . Thus, the posterior surface of smartphones should be cleaned using such options. However, it is unclear how often the posterior surface of smartphones needs to be cleaned, for which further studies are awaited.
The present study had some limitations. First, it had a small sample size and a single infection control culture, which might limit the generalizability of the findings. Studies to confirm the present findings are needed. The small sample size might also have been responsible for the lack of statistical significance of potential factors associated with bacterial contamination of the posterior surface. Second, the Hawthorne effect might have led to advanced cleaning of smartphones by participants with knowledge of this study. However, the impact of this bias may be limited by the unannounced microbial investigation of the smartphones and completion of this study in a short period. Third, smartphones were checked only for bacterial contamination. While clinicians during the present COVID-19 pandemic may be interested in viral contamination of smartphones, no measures to examine viral contamination were available for this study. However, the fact that the posterior surfaces of smartphones were more frequently contaminated with bacteria than touchscreens, regardless of the use of covers, will make us cautious about viral contamination of smartphones as well.