Volume 40, Issue 4 , Pages 389-390, May 2012
Removal of contaminating bacteria from computers by disinfection and hand sanitation
Article Outline
To the Editor:
Computer terminals are well-recognized potential vehicles for the transmission of pathogenic bacteria. Contamination of keyboards and mice with bacteria, including staphylococci, enterococci, and coliforms, has been documented in health care and non-health care settings.1, 2, 3, 4, 5 The recent article by Messina et al6 provides support for our previous findings that shared computers, such as those used found in classrooms and computer laboratories on university campuses, are readily contaminated by many common bacteria, including pathogens.5 As in previous reports,3, 7 the authors suggested that cleaning and hand hygiene are useful to reduce the risk of cross-contamination and recommended “thorough handwashing before and after keyboard contact.”
We conducted a study to test the efficacy of hand sanitation and disinfection of hand contact surfaces of computers (keyboards and mice) in reducing the number of viable bacteria, thereby decreasing the potential health risk of shared computer terminals. The study was conducted during a teaching semester at Swinburne University of Technology, Melbourne, in a shared computer lab that was used daily during the normal university week (Monday-Friday). Ten computers selected at random were sampled every Friday for 2 weeks before the implementation of cleaning procedures. Swabs of the computer keyboard and mouse of each tested terminal were obtained and plated onto MacConkey Agar (Mac) plates (Oxoid, Basingstoke, UK) for detection of coliforms and onto Mannitol Salt Agar (MSA) plates (Oxoid) for detection of staphylococci. Over the first 2 weeks of sampling, 100% and 90% of computers, respectively, were found to be contaminated with both coliforms and staphylococci, confirming previous reports of contamination of computers with human microbiota. Presumptive coagulase-positive staphylococci (CPS), presenting as yellow colonies on the MSA plates, were confirmed using the Staphytect latex slide agglutination test (Oxoid). Indeed, all computers were found to harbor CPS.
At the end of the second week, a commercial ethanol-based hand sanitizer (Aqium; Ego Pharmaceutical, Braeside, Australia), available in pump-packs, was introduced into the computer lab with notices requesting that all students sanitize the hands before using a computer terminals. Of the 10 test computers, every other terminal was also cleaned using commercial antibacterial wipes containing 70% ethanol (Scotch Brite; 3M Australia, North Ryde, Australia). Thus, we were able to compare the effects of hand sanitation plus disinfection versus hand sanitation alone on the recoverable viable bacteria. Sampling was continued for 3 weeks after implementation of cleaning/hand sanitation procedures. Students were blinded as to which computers were sampled and were unaware that additional cleaning of selected terminals was being performed. Although we were unable to accurately ascertain compliance to the hand sanitation request, monitoring of the pump-packs indicated that students were regularly using the sanitizers.
The results of testing after the first week of disinfection/hand sanitation showed moderate reductions in bacterial contamination. Overall, all computers that were not cleaned with ethanol wipes (ie, only hand sanitation) were still contaminated with coliforms and CPS. However, coliforms and CPS were detected on only 40% and 60%, respectively, of terminals on which additional disinfection was performed. Over the next 2 weeks, sampling failed to detect any coliforms on all computers. After the second week of cleaning, CPS were detected on 100% of terminals that underwent additional disinfection and 40% of terminals that did not. By the third week, these percentages had dropped to 40% and 20%, respectively. Thus, our results indicate that hand sanitation alone was efficient in eliminating coliforms and reducing the number of terminals contaminated by CPS. Additional cleaning with ethanol-based disinfectant further reduced the number of terminals contaminated with CPS.
Although the results reported by Messina et al are in general agreement with those of our earlier study,5 an important difference was that we found higher levels of contamination on shared keyboards, whereas Messina et al did not. This was attributed to differences in sample size or to “differences in hygiene habits between Australians and Italians.”6 Given our earlier finding that proper hand hygiene can greatly reduce microbial contamination, it is certainly worth instructing computer users to sanitize their hands before and after using a computer terminal, whether shared or nonshared.
An interesting finding was that cleaning procedures were very effective in eliminating coliforms, indicating that transient hand microbiota of likely fecal origin were more efficiently removed by simple cleaning methods. In contrast, CPS were not totally eliminated, possibly reflecting the greater resistance of gram-positive bacteria (with their thicker peptidoglycan cell wall layer) to ethanol-based sanitizers and disinfectants. It would be worthwhile to repeat the study using a greater variety of chemical disinfectants to examine whether they have greater efficacy against gram-positive species. In addition, the study was qualitative and was designed to monitor the presence or absence of the indicator bacteria. Although CPS were not totally eliminated from some terminals, their levels may have been reduced.
In conclusion, our study has shown that simple hand hygiene and cleaning practices are effective in eliminating or at least reducing the levels of both gram-positive and gram-negative bacteria from the contact surfaces of computers. We recommend that hand sanitizers be made available and users be encouraged to clean their hands before and after contacting computer surfaces, especially in multiuse facilities.
Acknowledgment
We thank Christopher Hoare, ITS Client Service Manager, for his invaluable assistance in the accomplishment of this work.
References
- . Computer keyboards and faucet handles as reservoirs of nosocomial pathogens in the intensive care unit. Am J Infect Control. 2000;28:465–471
- Bacterial contamination of ward-based computer terminals. J Hosp Infect. 2002;52:314–318
- . Bacterial contamination of computer keyboards in a teaching hospital. Infect Control Hosp Epidemiol. 2003;24:302–303
- Computer keyboard and mouse as a reservoir of pathogens in an intensive care unit. J Clin Monit Comput. 2004;18:7–12
- . Microbial contamination of computer keyboards in a university setting. Am J Infect Control. 2009;37:507–509
- . How many bacteria live on the keyboard of your computer?. Am J Infect Control. 2011;39:616–618
- Computer equipment used in patient care within a multihospital system: recommendations for cleaning and disinfection. Am J Infect Control. 2005;33:233–237
Conflict of interest: None to report.
PII: S0196-6553(11)01322-8
doi:10.1016/j.ajic.2011.11.018
© 2012 Association for Professionals in Infection Control and Epidemiology, Inc. Published by Elsevier Inc All rights reserved.
Volume 40, Issue 4 , Pages 389-390, May 2012
