A letter published this week by Prof. Wilson of UCLH finally proves how Hygiene Solutions’ (Deprox) director Rick Fentiman cheated both the UCLH and rival HPV system manufacturer Bioquell Plc, in a widely publicized comparative test in 2015. The results of this test apparently demonstrated that the Deprox, vapourising a 5% Hydrogen peroxide solution had identical germicidal efficacy as the Bioquell system vapourising 35% hydrogen peroxide solution.

I published an article in 2016 in which I analyzed the test results as published by Professor Wilson and colleagues in the Journal of Hospital Infection, and concluded that Fentiman had in fact filled the internal tank of the Deprox machine with a 35% solution prior to the test. New data published in the letter proves this claim beyond reasonable doubt.

In Wilson’s original test, neither the aerial concentration of H2O2 vapour , or the concentration of the liquid solutions was  measured.

In response to widespread concern and comment as to the rather surprising results obtained, Wilson recently again obtained the use of a Bioquell and a Deprox system and measured the concentrations of both the liquid and aerial vapour phases throughout their test cycles, as detailed in this week’s letter.

The Deprox was using 5% H2O2 solution, and produced peak vapour concentrations of 29 to 46ppm. The Bioquell machine was using a 35% solution, and produced 450 to 640ppm of vapour.

The maximum aerial concentration of H2O2 that can be generated is limited by the concentration of the original solution. Henry’s law can be used to prove that about 50ppm is the maximum sustained aerial concentration that can be generated from a 5% solution. The figure of 46ppm for Deprox from Wilson’s retest of the machine is thus exactly what would be expected.

In the original comparative test, both the Deprox and the Bioquell systems demonstrated practically identical efficacies of log 5.1 for spores and log 6.3 for vegetative bacteria. A very large number of biological indicators of several species were used over multiple tests, and no significant difference in performance between the two systems was found.

Therefore, inescapably, both systems must have generated the same aerial concentration of H2O2 vapour, and that must have been in the region of 400 to 700ppm. (There are numerous published papers demonstrating a log 6 efficacy for HPV systems using 30-35% H2O2 solutions)

It is physically impossible to generate anything close to these levels of vapour by evaporating or aerosolizing a 5% solution. Quite apart from Henry’s law, the volume of water that would have to be evaporated along with the H2O2 would quickly push the relative humidity to saturation, and prevent further evaporation from taking place.

Therefore, in the original comparative tests as published in the Journal of Hospital Infection, the Deprox was NOT running on a 5% H2O2 solution as claimed, but on a 35% solution, the same as the Bioquell system.

How then was this deception accomplished?

There are some aspects of the way in which the original UCLH tests were conducted that  are very suggestive:

At the time of the tests, Hygiene Solutions had a contract with UCLH, and had 4 Deprox machines permanently on site, which were operated daily by Hygiene Solutions employees. UCLH had a definite rule that the equipment was not to be operated by their staff – hence no UCLH staff were trained in the use of the equipment.

The paper states:  “The HPS1 unit was operated by a trained engineer (Bioquell), while the HPS2 module was operated by hospital staff following training by a dedicated member of the issuing manufacturer (i.e. Hygiene Solutions).”

I have two independent witnesses that the two Deprox machines were used in the trial were not the machines already on site, but were specially prepared at the Kings Lynn depot, with all new piezo discs and calatytic deactivation media. The machines were driven up to UCLH personally by Rick Fentiman, who stayed for the duration of the tests then drove the machines back to Lynn. Apparently no other Hygiene Solutions staff were involved. The “dedicated member” therefore was Rick Fentiman, and he instructed and supervised some unidentified member of the “hospital staff” in the operation of the equipment “on the spot”.

The paper says: “However, during this study, both parties provided storage of equipment and hydrogen peroxide stock solutions off-site.” In the case of the Deprox units, this was  the large van in which they were transported. Clearly then there would have been opportunity for Mr Fentiman to have filled the internal storage tank of the test machines with a 35% solution and disposed of or diluted any residual fluid after the test, without either his own employees or the UCLH staff being aware of the substitution.

It is pertinent that (unknown to the UCLH) the Deprox has a substantial internal storage tank, of about 8 litres capacity.

Illustration from the Deprox patent.

The evaporation unit draws from the bottom of this tank, and the 2 litre Deproxin refill bottles trickle feed in to the top of the tank. I assume that for the sake of authenticity, a genuine Deproxin refill was inserted in to the top of the machine for the tests, hence even if Prof Wilson had tested the concentration of the fluid, he would have found it to be as stated. As concentrated H2O2 solution is substantially denser than water, a trickle of dilute solution in to the top of the tank would have no significant effect over the course of a few cycles of the machine.

Deprox salesman Tom Lister stalls when faced with a direct question about the UCLH tests. The machines had been filled with a 35% hydrogen peroxide solution, where UCLH were told it was a 5% solution. Tom knows this, and his guilty conscience shows very clearly in his body language and facial expressions. Rather than answer he says “Where did you say you were from?” although I had just told him, and was wearing a badge with the answer in large type!