Here I continue with 2 more common misconceptions that I have heard saying in different forums or at some point during the technical negotiation phase for biodecontamination projects. They are very common and perhaps, some reader will be surprised. I hope these explanations are quite clear, but, in any case, there is a lot of literature that corroborates that these beliefs are not correct. For more information, the reader can download some related articles here.

Misconception nº3 – The more concentration of H2O2 in gas phase we have in the isolator, chamber, or room, the faster and better we will decontaminate.

As explained before, biodecontamination is not a process that depends solely on concentration. Initial temperature and relative humidity are factors that also influence on the lethality of the process.  A typical case is that of an isolator coupled to an autoclave chamber or a freeze dryer. A simple test can be done to show that, although the concentration reached is the validated one, if the surface of the autoclave door is hot, the indicators located there do not turn. Why? Because being on that warmer surface does not produce microcondensation of H2O2 and, therefore, not enough liquid-phase contact occurs to kill the entire population of spores. Therefore, the reading of the concentration, which measures quantity in gas phase and at a certain point, gives biased information.

This is a lesson learning for those who entrust everything to concentration sensors. The information they provide is only one of the parameters of the process, which can be used for monitoring, but taking it as the main driver of the cycle control can lead to distortions. Currently, there are sensors that not only monitor the concentration, but also the humidity, temperature, and saturation of the vaporized mixture of H2O+H2O2 (the PEROXCAP HPP 272 from Vaisala). These sensors give a more complete information that you must know how to interpret, but let’s not forget, it is taken at a very specific point.

A derivative of the missconception of searching for high concentrations is the unnecessary complication of cycles. To achieve high concentrations, dehumidification systems must be provided, which involves more components and sophistication. It is obvious that, if we inject hydrogen peroxide having a high initial humidity, we will have less space available to vaporize it before it saturates and condenses. However, I have been able to observe cycles with 10% initial humidity and dwell phases with concentrations of up to 1200 ppm that have had difficulties in achieving a lethal effect in a homogeneous way.  In that specific case, the control of the cycle was carried out from a concentration sensor at the output of the generator. The recipe allowed to set up a target concentration and to keep it constant, new peroxide was introduced from the top while drained at the bottom. With the enzyme indicators we verified that, due to the flow of air from top to bottom, the VH2O2 was not properly reaching the upper parts. Despite the glaring lack of uniformity of the cycle, if you only looked at the graph, everything seemed perfect. The graphs were brilliant, with very pronounced preconditioning and aeration phases as well as a very flat exposure phase, with practically no variation in concentration.  However, the development of the cycle was a long process due to the lack of reproducibility of the BI results and at the end, there was no choice but to extend a lot the exposure phase, leading to an excessive consumption of peroxide.

In short, the misconception of considering that the more concentration we achieve, the faster and better we will decontaminate may lead to design of systems and cycle developments with very low efficiency.

Misconception nº4 – VHP hydrogen peroxide vapor is sterilizing while misting is only sanitizing. 

This misconception is one more derivative of considering that a vapor in ambient conditions behaves like a gas and, therefore, achieves similar effects to those of ethylene oxide, for example. In fact, the manufacturer that led the development of the VHP technology did so thinking initially in finding an alternative to ethylene oxide sterilization. Around that time, in the early 1990s, many hospitals began to phase out their ETO sterilization equipment due to its occupational hazards and the increasing awareness of its risks. The only alternative was the massive use of single-use medical devices. However, there were many devices, such as endoscopes, that needed to be reprocessed and needed to be sterilized. Several manufacturers saw that peroxide could be an alternative and equipment initially designed to sterilize lumens and internal spots came onto the market. But they all failed to ensure the sterility level of 10-6 in a wide variety of heat-labile products. The problem was (and still is) that, unlike ethylene oxide, peroxide vapor does not behave like a gas and diffuses/penetrates in a poorly way. Today,  in the hospital sector there are VHP sterilizers, but because of their use is quite limited and regulators like the FDA severely restrict their use to certain product types and forms, total volume of loads, etc. If you are interested in knowing how VHP is used to sterilize in the hospital sector and the difficulties it entails, I recommend this article: Keys to success with vaporized hydrogen peroxide sterilization.

On the other hand, the VHP showed greater viability for another application: the airborne disinfection of surfaces, and in the pharmaceutical sector, especially for isolators. In that context, the VHP was an alternative to other chemical disinfectants such as formaldehyde and peracetic acid, which had some contraindications. Those latter left residues on surfaces and could be highly toxic even at low concentrations. Thus, the success and widespread use of VHP or VH2O2 versus other chemical disinfectant methods is not due so much to its greater power or ability to sterilize/disinfect, but rather to the fact that it does not leave residues, is not carcinogenic and, although it is toxic, it is so at much higher concentrations.

In short, either it’s produced with hot flash vaporization or it’s cold vaporization by nebulization technology, hydrogen peroxide vapor does not have sufficient penetrating capacity to guarantee reduction levels of 10^-6 in items with complex shapes and/or significant bioburden and therefore, in no case is can be considered a sterilization process.

P.S. As I’m aware that this last statement can contribute to even more confusion. In my next post I will explain more precisely the difference between sterilization and biodecontamination in the pharmaceutical context and I will comment on the controversy that exists with the new Annex 1 of the GMP regarding not considering peroxide as a sterilizing process.