The sale of ethyl alcohol is regulated by the Alcohol, Tobacco and Firearms Agency. The ATF wants to be sure that one is not purchasing ethanol for lab use and diverting it to beverage use without paying the tax. It is possible to purchase pure ethyl alcohol, but there are severe record keeping and tax restrictions. In order to avoid the taxes and/or record keeping, the ATF authorizes the use of denatured alcohol for laboratory use. Denatured alcohol is ethanol with something added to make it undrinkable. Denatured alcohol is also referred to as “SD” alcohol (for specially denatured).
The purest of the denaturing formulas is SD3A, which is 95% ethanol with 5% methanol. SD3A is authorized for manufacturing use at facilities that are licensed for its use. It may not be sold to the general public. The purest authorized denaturing formula that may legally sold to the public is reagent alcohol, which is 95% SD3A with 5% isopropanol. Reagent alcohol is a suitable replacement for pure ethanol in almost all laboratory procedures. The only exceptions we are aware of are: The preparation of alcohol standards (obviously), and drug use.
Formaldehyde is a gas at room temperature and one atmosphere of pressure. The saturated solution of formaldehyde, about 37% formaldehyde, is properly called formalin. The 1:10 dilution of formalin has 4% formaldehyde and is properly called formalin 1:10. It is also called 10% formalin. This is the solution most used for formalin fixation of tissue and is commonly referred to as “formalin fixative.” This should not be confused with 10% formaldehyde which is actually a solution containing 10% formaldehyde and is only rarely used for tissue fixation.
Choose a germicide with the level of disinfection appropriate to the device being disinfected. See the labeling for the device or contact the manufacturer for instructions.Sterilants kill all micro-organisms when used according to directions. High-level disinfectants are effective against viruses, vegetative bacteria (including tuberculosis) but not against large numbers of spore forming organisms. Low-level disinfectants are not effective against spore formers or tuberculosis. They may not be effective against all viruses.
Critical devices are those that present a high risk of infection such as items that routinely penetrate the skin, mucous membranes or other areas of the body that are normally sterile. Critical devices should always be sterilized before use. Steam, ethylene oxide or any other method that can be biologically monitored is the preferred methods for these devices. Because liquid chemical sterilants can not be monitored properly, they are not recommended for these items except in exceptional situations (e.g. items that are heat sensitive or otherwise not compatible with the other methods of sterilization).
Semi-critical devices contact with mucous membranes but do not contact normally sterile areas of the body. Sterilization of semi-critical devices is preferred but high level disinfection is acceptable.
A non-critical device contacts only intact skin. High level or low level disinfection is usually sufficient.
It has been known for some time that the efficacy of glutaraldehyde based germicides is greatly enhanced by the addition of surfactants. By lowering surface tension, surfactants allow for better contact between the microbe and the germicide which decreases the required immersion time and increases the reuse life of the solution. Products using surfactant and glutaraldehyde first appeared on the market in the mid 1970’s. Initially there were two types of problems when these products were used on endoscopes. Specifically the surfactant initially caused problems with the electrical contacts and with clouding of the lenses. Manufacturers of endoscopes promptly reengineered their products to eliminate both problems. The electrical problem was caused by build up of surfactant and was solved by better rinsing of the instrument.
The lens problem was caused because the lower surface tension permitted the germicide to penetrate between the elements of the lens. Changing the cement used to hold the elements together solved this problem. No area of interest is without its urban legends and the the medical world has its share. Like all urban legends there is a kernel of truth to the myth that surfactants damage endoscopes. When these products were first introduced there were some problems but they were corrected and the use of surfactant containing disinfectants has not been a problem for over twenty years. However, some manufacturers of germicides have had a vested interest in perpetuating the myth in order to continue selling non-surfactant products. Others pass it on because they heard it from a friend of a friend.

In the wake of a report of endoscopy-related transmission of hepatitis C virus1, we have received requests for information about the efficacy of glutaradehyde based disinfectants, such as Wavicide-01, against HCV. The incident in question was caused by poor processing of the scope and not by disinfectant failure2. The endoscope had not been properly cleaned and had been immersed in disinfectant for only five minutes. According to APIC, glutaraldehyde is still recommended as one of the preferred agents for high level disinfection of endoscopes3.

  1. Bronowicki JP, et al. Patient-to-patient transmission of hepatitis C virus during colonscopy. N Eng J Med 1997; 337:237-240.
  2. Alvarado CJ. Reichelderfer M. APIC guideline for infection prevention and control in flexible endoscopy. Am J Infect Control 2000; 28:138-55 (http://www.apic.org/pdf/gdendosc.pdf).
  3. Ibid, pg. 147.

A common question that is routinely asked is what is the difference between a 14 days and a 28 days glutaraldehyde solution? Which should I use? Why is Wavicide-01 a 30 days solution? Please explain?
Originally, when the first glutaraldehyde product appeared on the market, it was a 14 day alkaline solution. It was discovered that when the pH of a glutaraldehyde solution is raised to very high levels, above 9, the cidal activity is increased.. but the glutaraldehyde begins to polymerize at a much faster rate. Two weeks after activation, whether is has been used or not, the MEC (Minimum Effective Concentration) of the glutaraldehyde is now below the threshold where the product is effective as a disinfectant and the solution should be discarded. With the addition of some surfactants and a lower pH the glutaraldehyde product becomes a 28 days solution, after activation whether it has been used or not. 100% Tuberculocidal inactivation goes from 45 minutes for the 14 days solution to 90 minutes for the 28 days solution.

Wavicide-01 works at an even lower pH and is pre-activated, the unused product remaining in the bottle is good for one year from the manufacturing date. Like a 14 days solution, TB is inactivated in 45 minutes, yet the product is good for thirty days from the date of first use. It is very important that the concentration of all glutaraldehyde disinfectants be monitored daily or even more often depending on your application using monitor strips to make sure it remains above MEC (a glutaraldehyde product below its Minimum Effective Concentration is ineffective). For applications like endoscope disinfection where typically a pre-washed wet device is submerged in the solution, the product is continually being diluted and the glutaraldehyde concentration will drop at a very high rate, much shorter than the 14, 28 or 30 days mentioned on the label.

We would like to steer users away from the notion of “days of use” to the importance of monitoring glutaraldehyde concentration which is the important factor in determining whether or not the product is effective. The “day of use” period reflect the maximum period of time the product can be in use regardless of the fact its concentration is still above MEC.

As laboratory personnel become more widely cross-trained, the availability of people who have expertise in diagnostic parasitology will become more limited. Over the years, questions have been raised regarding various aspects of diagnostic medical parasitology. In this section we will attempt to answer many of these questions. We hope this will be helpful for those working in this area of microbiology and provide some “tips of the trade” that are learned through many years of bench experience.

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