Tracking the number of laboratory-acquired infections (LAIs) in the United States is no easy task. Not all incidents are reported, and sometimes the victim may not be aware of the source of the infection. Despite that, the United States Bureau of Labor Statistics (BLS) does collect available information about those reported exposures in labs. The numbers have been declining over the past decade,1 but exposures do still occur.
It is possible to become infected with a pathogen simply by touching contaminated surfaces in the laboratory without personal protective equipment (PPE). According to the Clinical and Laboratory Standards Institute (CLSI), in the laboratory “telephones, doorknobs and handles, computer terminals, and other surfaces are considered contaminated.”2 One important way to minimize this exposure risk to lab employees is to utilize good decontamination practices.
Decontamination is the act of minimizing the overall pathogenic microbial presence. For labs that process routine patient specimens, that microbial presence may exist in the form of bloodborne pathogens, bacteria, fungi, and even prions. The purpose of the decontamination process is to reduce the number of these contaminants in order to minimize the possibility of transmission or infection.
Routine decontamination of lab counter tops or work areas should occur frequently. Lab benches should be cleaned at a minimum after each working shift and after spills occur. This routine decontamination process should be documented as well. It is also a good idea to regularly include telephones, computer terminals, and other frequently handled surfaces in the lab in the disinfection process.
Typically, chemical germicides are recommended for the surface decontamination in the lab setting. These germicides are classified as high-level, intermediate, or low-level disinfectants based on their activity and strength. The most commonly recommended disinfectant for lab surfaces is a 10-percent solution of sodium hypochlorite (or bleach), which is considered an intermediate-strength chemical germicide. Intermediate-level disinfection will eliminate most bacteria (including Mycobacterium tuberculosis) and all fungi, and it inactivates viruses.
Laboratories should use an EPA-registered or approved disinfectant. Manufacturers list their products with the U.S. Environmental Protection Agency (EPA), and the agency verifies that the disinfectant is effective against common pathogens and complies with Occupational Safety and Health Administration (OSHA) Bloodborne Pathogen standard requirements. These requirements include the ability of the product to effectively decontaminate contaminated surfaces and spills.3
Many manufacturers offer pre-made bleach cleaning products, but many laboratories still make their own dilutions from concentrated bleach. That is an acceptable practice, but fresh bleach solutions should be made daily, as the efficacy of the solution wanes quickly. It is also important when making mixtures to consider the concentration of the purchased bleach. Traditionally, labs made a 1:10 solution, as most bleach products were sold in the past at a 5.25 percent concentration. Since many available commercial bleach concentrations now are at 8.25 percent, labs should make a 1:16 solution for disinfection purposes if they are using that bleach. Laboratorians should be sure to check the label of the bleach product purchased before making dilutions. Sodium hypochlorite is a corrosive chemical, and even in its diluted form it can cause damage to some surfaces over time. In order to prevent this, the disinfected surface should be rinsed off with sterile water or 70 percent ethanol (another intermediate chemical germicide).
Some special cases
In disinfecting a biological safety cabinet (BSC), a bleach solution may be used. Along with disinfection of the work surface of the cabinet, the back and side walls and inside of the glass sash should also be cleaned. Again, rinsing with water or ethanol will help prevent the pitting of the stainless-steel surfaces of a BSC that can be caused by bleach. Ultraviolet lights should never be used for bacterial disinfection inside of a BSC. It is well-documented that the efficacy of UV light decontamination is blocked by dust, shadows, and light intensity.4 There is also the danger of UV light exposure for the user of the BSC, which should be avoided. However, UV lights in a BSC can be used effectively for DNA decontamination in certain Molecular Laboratory processes.
In the Anatomical Pathology section of the laboratory, formaldehyde is sometimes used as a disinfectant. Depending on its concentration, formaldehyde can be considered a high-level disinfectant. The chemical, a known carcinogen, is placed inside a cryostat, and fumes generated buy a heat source are used to decontaminate the inside of the apparatus. However, the effectiveness of the disinfection is unclear, and the dangers of using a carcinogen mark this method as less than satisfactory. Check with the cryostat manufacturer for cleaning guidelines, but many instruments can be disinfected using 70 percent alcohol.
A special consideration with disinfection is the handling of prions. Prions are abnormally folded proteins which cause diseases known as transmissible spongiform encephalopathies (TSEs). The most commonly known TSE is Creutzfeldt-Jakob disease (CJD), and laboratories may handle specimens from CJD patients. Prions are not inactivated easily, and sample testing in the lab should be performed using disposable equipment where possible. Tissues removed from CJD patients should be fixed using 95 percent formic acid before processing. Non-disposable implements used with such samples should be immersed in 1N sodium hypochlorite (NaOH) for one hour before reuse. Surfaces on which samples were handled or spilled should also be immersed in NaOH for one hour for disinfection purposes.
While concentration of chemicals plays a role in effectiveness against pathogens, one final consideration with all lab disinfectant products is the contact time with the pathogen. Most disinfectants do not instantly kill the organisms on contact; the product must be left on the contaminated surface for a specified amount of time in order to complete its action. EPA-registered disinfectants all have designated contact times printed on the label. For example, a surface disinfectant may have a contact or kill time for hepatitis B virus of one to three minutes; however, its tuberculocidal contact time may be ten minutes. Be sure to check labels and understand the contact time requirements. Using these products properly is the only way to ensure proper disinfection.
A dangerous place…
The laboratory setting is an intrinsically dangerous place where bloodborne and airborne pathogens are omnipresent, and specific actions must be taken in order to protect the people working in the department. In order to prevent LAIs, engineering controls, work practice controls, and PPE should always be employed. Decontamination of surfaces is another significant control that must be utilized properly. Understanding the proper types, concentrations, and contact times of the appropriate lab disinfectants is a practice that will reduce those threatening pathogens and make the laboratory a safer place to work.
- U.S. Department of Labor Bureau of Labor Statistics. Injuries, illnesses, and fatalities. https://www.bls.gov/iif/.
- CLSI. Clinical Laboratory Safety; Approved Guideline—Third Edition. CLSI document GP17-A3. Wayne, PA: Clinical and Laboratory Standards Institute; 2012.
- U.S. Department of Labor Occupational Safety and Health Administration. Toxic and hazardous substances: bloodborne pathogens. https://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=standards&p_id=1005.
- U.S. Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Institutes of Health. Biosafety in Microbiological and Biomedical Laboratories (BMBL). 5th ed. Washington, DC: US Department of Health and Human Services; 2011.
Daniel J. Scungio, MT(ASCP), SLS, CQA (ASQ), has more than 25 years’ experience as a certified medical technologist. He was a laboratory manager for 10 years before becoming the laboratory safety officer for Sentara Healthcare, a system of twelve hospitals and more than 20 laboratories and draw sites in Virginia and North Carolina. As “Dan the Lab Safety Man” he provides consulting, education, and training throughout the U.S. and Canada. Visit Dan the Lab Safety Man’s Facebook page at www.facebook.com/danthelabsafetyman.