Shocking Ultra-V test results!

A comprehensive trial of the Hygiene Solutions Ltd Ultra-V decontamination system has exposed shocking discrepancies between the manufacturer’s claims and the actual performance of the system. Prof Peter Wilson, a consultant microbiologist at University College London Hospitals NHS Foundation (UCLH) tested the system against a variety of bacteria and spores using both contact plates and Biological Indicator discs. Six single patient isolation rooms were decontaminated and the results aggregated. The thorough in-vivo testing and the high reputation of the author and the UCLH Environmental Microbiology laboratory leave no doubt whatever as to the accuracy of the results.

Here are Hygiene Solutions’ claims, and the UCLH test results compared:


Can achieve between a 6-log and a 4-log reduction of a broad spectrum of pathogens

Inactivates Clostridium difficile infection (C.diff.), Methicillin-resistant Staphylococcus aureus (MRSA) and Vancomycin-resistant Enterococci (VRE) even in light soiling

Test Result

C. difficile spores in low soiling, log reductions between log 0.1 and log 1.1 (see Table III below)


Placed in one central location within each room, Ultra-V can effectively decontaminate all surfaces in the enclosed healthcare area within the shortest treatment time.

Test Method

“Hygiene Solutions Ultra-V™: a single-emitter device (UVC, λ=265nm) relocated intermittently as determined by sensors in room.”


How long does the process take? Average side room would normally take 20 minutes to complete.

Test Result

Process time, NOT including preliminary manual clean, 1 hour and 19 minutes. (See table 1 below)


Hygiene Solutions claims imply a validated log 4 to 6 reduction of C. difficile, even in light soiling, on all surfaces in a single patient room in about 20 minutes – without moving the unit from a central location.

In reality, even with a 79 minute process time, and multiple relocations of the unit to eliminate shadowed areas, the greatest log reduction achieved for C.difficile spores was log 1.1. That is about ONE THOUSANDTH of the claimed performance – in spite of the process time being extended 4 fold.

Table 1

Table III

Download the entire paper as a pdf:

Comparison of Two Whole-Room UV-Irradiation Systems for Enhanced Disinfection of Patient Rooms Contaminated with MRSA, carbapenemase-producing Klebsiella pneumoniae and Clostridium difficile spores

S. Ali, S. Yui, M. Muzslay, A.P.R. Wilson

Or read the article on the Journal of Hospital Infection site:


Ultra-V tested by UCLH, exposed as fraud!

Breaking news – in a Journal of Hospital Infection article published August 16th, Prof Wilson of UCLH shows that the Ultra-V UV room disinfection system takes a whopping 1 hour and 19 minutes to achieve even BASIC levels of decontamination, requires multiple re-positioning of the unit during the cycle, does NOT decontaminate shadowed areas, and is particularly ineffective against C. difficile spores. (log 0.1 to log 1.1)

MEANWHILE – Hygiene Solutions claim a 20 minute cycle time, NO re-positioning, and log 4 to 6 efficacy.


Fentiman’s UCLH Hoax


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!


Wilson exposes Deprox fraud!

Deprox Hygiene Solutions

In a letter published today in the Journal of Hospital Infection, Professor Peter Wilson and colleagues report on their retesting of the Deprox (Hygiene Solutions Ltd) HPV decontamination system. The retesting was in response to concerns widely raised that the earlier tests of the system, which purported to give a log 6 efficacy, were the result of the manufacturer misrepresenting the concentration and/or constituents of the Deproxin solution.

In brief, the retest reveals the following:

  • The efficacy of the system, when using the correct 5% H2O2 solution, is around log 4 – similar to other, much less expensive fogging systems on the market. Hygiene Solutions Ltd will now be taxed to explain why on the initial test by Prof. Wilson, a log 6 efficacy was found. This 100 fold drop in efficacy comes between the first test series, in which the solution concentration was not checked, and the second series in which the concentration was independently measured. It seems highly likely that in the initial test series, the Deprox was running on a 30% H2O2 solution, rather than a 5% H2O2 solution as claimed.
  • The aerial H2O2 concentration on re-entering the room at the end of the cycle was 3.3ppm which is in excess of both short term and long term H2O2 exposure health limits. This is in spite of a hasty retrofit of catalysts to the whole Deprox fleet, and the manufacturer’s claim that their system monitored the H2O2 levels, and would only allow re-entry when the level was below the 1ppm safety standard.
  • Deproxin is confirmed to contain 10-20ppm silver nitrate, and this is indeed deposited on surfaces in the room, and may well be a contributor to the efficacy achieved. Hygiene Solutions informed the HSE over a year ago that Deproxin does not contain silver nitrate. This has now been exposed as untrue – and raises the question as to whether it is currently legal to sell or use the Deprox system.
  • Poor efficacy results for two more sheltered locations is attributed to inhomogeneous vapour distribution, due to inadequate circulation of the vapour. This raises serious doubts as to Hygiene Solutions’ claims that the Deprox will decontaminate “inside small crevices and complex equipment”

It is very much to the credit of Professor Wilson and colleagues that they have thoroughly retested the system in response to widespread concerns. It is sad that commercial interests would abuse the trust and confidence of highly qualified academics in this way by misrepresenting the basic test parameters.

For those without access to the Journal of Hospital Infection, I have reproduced the letter below, and a PDF is downloadable here.


In response to the letter from Dr Singh commenting on our paper.[1], [2]

The objective of our study was to evaluate the reductions in environmental contamination during in-use operation of two commercially-available hydrogen peroxide whole-room disinfection systems.2 Both manufacturers agreed test parameters prior to the trial to ensure methodology followed manufacturer instructions. Our findings suggested similar efficacy of the two systems against both surface contamination and biological indicators of common pathogens. Inocula used on the indicators far exceeded the likely levels seen in the environment.

Additional studies were performed as part of the original work using the same methodology with four strains each of MRSA, Klebsiella pneumoniae, Clostridium difficile spores and Acinetobacter baumannii. Three HPV decontamination cycles were evaluated for each system. Of 305/320 samples, >4-log10 reduction was achieved.

Aerial concentrations of hydrogen peroxide and relative humidity were monitored continuously during a further 6 cycles of both systems using a sensor (C-16 Portasens II Gas Detector; Analytical Technology Inc., Collegeville, PA, USA). In addition, horizontal surfaces in the near-patient vicinity were swabbed and analysed to detect fallout of silver and nitrate at the end of HPV decontamination cycles (n=3). Surfaces were swabbed and analysed for silver by titration (Silver Test Kit, DTK Water, Wellingborough, UK) and nitrate using Quantofix semi-quantitative test strips (Macherey-Nagel, Düren, Germany).

For the Deprox (Hygiene Solutions, King’s Lynn, UK) system, peak aerial values of 29-46 ppm hydrogen peroxide were achieved with similar bacteriological efficacy as other cycles. The mean level at the end of the cycles was 3.3ppm for 41.8% (30.8-58.1%) mean relative humidity at start of cycles. Silver and nitrate were detected on surfaces at 1.5-2.5mg/m2 following cycles with the Deprox system.

For the Bioquell Q10 system with the R10 aeration unit (Bioquell, Andover, UK), the peak aerial levels of hydrogen peroxide were 450-640ppm. The mean level at the end of the cycles was 0.0ppm with starting mean relative humidity 42.5% (34.5-49.7%). No silver or nitrate was detected on surfaces following cycles with the Bioquell Q10 system.

The aqueous concentration of hydrogen peroxide in a Hygiene Solutions cartridge (Deprox) tested on one occasion at the point of insertion into the machine was 5%. Nitrate was detected in the aqueous solution at 10-25mg/L. The aqueous hydrogen peroxide concentration in the Bioquell Q10 cartridge (Bioquell HPV-AQ) was 35% and no silver or nitrate was detected.

Dr Singh suggests C. difficile spores (but not the other organisms) persisted underneath the bed and on the window frame after decontamination using the Deprox system. The persistence of spores may have been minimised during the Bioquell Q10 cycles by the inclusion of an oscillating fan to facilitate aerial distribution and aid breakdown of hydrogen peroxide vapour.

As Dr Singh suggests, settling of active silver onto biological indicator coupons during a cycle of aerial HPV decontamination may have contributed to the bactericidal/sporicidal activity of the Deprox system. However further studies would be required to elucidate its role.

JHI letter damns Wilson’s Deprox test

A letter published on May 31st in the Journal of Hospital Infection shows Prof Peter Wilson’s controversial Deprox test results can be attributed to the very high level of (now illegal) silver nitrate in the Deproxin disinfectant solution. Wilson’s paper had already been strongly criticised by Dr Jon Otter of Imperial College, who suggested that Deprox manufacturer Hygiene Solutions Ltd. had added “A dash of peracetic acid” to the mix in order to achieve the improbable results.

However, as Dr Singh points out in the letter, the explanation is that Deproxin contains a whopping 2000ppm of silver nitrate, forty times as much as the ASP Glosair system that Dr Otter was comparing it to. The spray of silver nitrate solution settles on the BIs (conveniently unpouched and placed face up) and is concentrated by evaporation to highly germicidal levels. Meanwhile the volatile hydrogen peroxide component is dispersed and diluted through the volume of the room, and may play relatively little part in the process.

This substantial silver nitrate content is confirmed by a Daily Mail report from the Royal Liverpool Hospital, where a patient complained of “black grime” on the inside of the windows. The Hospital explained that it was a “sterile residue” from the hydrogen peroxide decontamination process. The hospital was using the Deprox process at the time.

Deprox mail

By an interesting coincidence, the JHI “articles in press” also has another paper on the antimicrobial efficacy of silver nitrate. This paper shows the MIC (Minimum Inhibitory Concentration) of silver nitrate for a range of vegetative bacteria, as below:

“The silver nitrate MIC was tested on a total of 443 isolates, ranging from 16 to 32 mg/L for the majority of the tested strains with or without sil genes. For Enterobacter and Klebsiella spp., elevated MIC (≥64 mg/L) for silver nitrate was recorded in E. cloacae (15/99, 15%), E. aerogenes (2/29, 7%), K. oxytoca (2/59, 3%), and K. pneumoniae (2/95, 2%).”

Note that 1mg/L = 1ppm. These bacterial strains were inhibited by just 16 to 32ppm AgNO3, compared to 2000ppm in Deproxin. No wonder the BIs were sterilised!

Hygiene Solutions Ltd is now between the devil and the deep blue sea. Do they remove the silver nitrate from the Deproxin, in which case their already shaky “validated to achieve a log 6 reduction” claim collapses, or do they continue the ludicrous pretense that the silver nitrate is actually just “silver” – in spite of the obvious point that metallic silver is a powerful catalyst for the decomposition of hydrogen peroxide?

This is a dilemma for hospital staff also, as according to the HSE it is illegal to use a PT2 (i.e. fogging or airborne) product containing silver nitrate. There can be no question that silver nitrate is an “active ingredient” in Deproxin. The Deprox unit contains a palladium catalyst to remove the hydrogen peroxide at the end of the process – however, this catalyst will not remove the silver nitrate, leaving an extremely fine dust or droplets of silver nitrate solution in the air when the room is re-entered. This chemical is highly toxic by inhalation, with a legal limit of just 0.01mg/m³. Certainly it would be risky to re-enter treated rooms without some kind of measurement process to assess the air quality.

Deprox nitrate

For those without access to the JHI, I have reproduced Dr Singh’s letter below.


I note with interest the May 2016 article by S. Ali et al. “Efficacy of two hydrogen peroxide vapour aerial decontamination systems for enhanced disinfection of meticillin-resistant Staphylococcus aureus, Klebsiella pneumoniae and Clostridium difficile in single isolation rooms.”[1]

The two systems compared in this study use very different concentrations of hydrogen peroxide, and yet showed almost indistinguishable efficacy in these tests.

This would lead to the conclusion that the bactericidal and sporicidal efficacy of H2O2 is independent of concentration, which seems improbable – indeed, previous comparative evaluations of a high-concentration (30%) hydrogen peroxide system (Bioquell) with a low-concentration (5%) hydrogen peroxide system (ASP Glosair) by Fu et al.[2] Holmdahl et al.[3] and Beswick et al.[4] have demonstrated that the low-concentration fogging only achieved log reduction factors (LRF) of between 2 and 4, which was much smaller that the LRF of 6 generally achieved with the higher hydrogen peroxide concentration.

I would suggest that the unexpectedly high efficacy of the 4.9% hydrogen peroxide system evaluated by S. Ali et al. may be attributable to the relatively high level of silver nitrate in the proprietary Deproxin solution. The Deproxin MSDS[5] states: “CAS: 7761-88-8 Silver <0.2% EINECS: 231-853-9”. While “Silver” is given as the description, the CAS and EINECS numbers show that this is in the form of silver nitrate. In terms of ppm, 0.2% equates to 2000ppm. By contrast, the ASP Glosair system evaluated in the three papers mentioned above contained “<50ppm silver nitrate”. The solution used by S. Ali et al. thus apparently contained around forty times more “silver” than solutions used in systems previously evaluated.

Even at 2000ppm, the silver nitrate in Deproxin is considerably less concentrated than the hydrogen peroxide, by a factor of 25. (0.2% AgNO3: 4.9%H2O2) However, there is an important difference in the mode of distribution for these two active ingredients that may tend to preferentially concentrate the silver nitrate in the vicinity of the biological indicators. The hydrogen peroxide is volatile and unstable, and as the fog droplets evaporate, it is distributed throughout the whole volume of the room (about 60m3 in the example given), where the concentration then drops substantially with elapsed time as it spontaneously decays to oxygen and water. The silver nitrate however is not at all volatile, and is persistent.

The final distribution of the silver nitrate is hard to predict, but it may be assumed that much of it eventually drops to the floor or other horizontal surfaces in the room, either as solid particles or as droplets of solution that have been concentrated by partial evaporation. In the tests performed by S. Ali et al., biological indicators(BIs) were placed in horizontal, upwards facing orientation. If these BIs became saturated with a film of Deproxin solution from the fogging process, it can be expected that as the water evaporated during the “deactivation” cycle, the concentration of the silver nitrate would rise from the initial figure of around 2000ppm to substantially higher levels. It is of note that according to S.R.K. Pandian et al.[6] the MIC (Minimum Inhibitory Concentration) of silver nitrate for the spore-forming Bacillus licheniformis is only 5mM, which is equivalent to 850ppm.

There is some circumstantial evidence to support this explanation. S Ali et al. referring to the Deprox system state; “When rooms were disinfected using HPS2, C. difficile persisted most frequently underneath the bed and window frame in 6/21 cases (28.6%).” The “window frame” position is described as being “approximately 2m above floor” where the room height is given as 2.7m. The two positions pointed up as showing the lowest LRFs for the fogging system were those positions with the most restricted headspace – 0.7m in one case and presumably the same or less under the bed. These positions would have received the least precipitation from settling fog droplets or dust, so may have received proportionally less of the silver nitrate.

It would be very instructive to repeat the experiment without the hydrogen peroxide, and thus determine the log reduction attributable to a 2000ppm silver nitrate solution alone.

Conflict of interest



  1. S. Ali, M. Muzslay, M. Bruce, A. Jeanes ,G. Moore, A.P.R. Wilson et al. Efficacy of two hydrogen peroxide vapour aerial decontamination systems for enhanced disinfection of meticillin-resistant Staphylococcus aureus, Klebsiella pneumoniae and Clostridium difficile in single isolation rooms. J Hosp Infect. 2016; 93: 70–77
  2. Fu, T.Y., Gent, P., and Kumar, V. Efficacy, efficiency and safety aspects of hydrogen peroxide vapour and aerosolized hydrogen peroxide room disinfection systems. J Hosp Infect. 2012; 80: 199–205
  3. Holmdahl, T., Lanbeck, P., Wullt, M., and Walder, M.H. A head-to-head comparison of hydrogen peroxide vapor and aerosol room decontamination systems. Infect Control Hosp Epidemiol. 2011; 32: 831–836 Beswick, A.J., Farrant, J., Makison, C. et al. Comparison of Multiple Systems for Laboratory Whole Room Fumigation. Applied Biosafety. 2011; 16
  4. Sevron Safety Solutions.[accessed 11.05.17]
  5. Pandian, S.R.K., Deepak, V., Kalishwaralal, K. et al. Mechanism of bactericidal activity of Silver Nitrate – a concentration dependent bi-functional molecule. Braz J Microbiol. 2010; 41: 805–809

Freedom of Information request reveals exact C. difficile/Deprox correlation.

C. difficile 1

A Freedom of Information request¹ to UCLH disclosed the starting and finishing dates of their disastrous Deprox decontamination contract with Hygiene Solutions Ltd. The Deprox operations started in June 2013 and ran continuously, 7 days per week through to October 2016. The contract called for at least 4 Deprox units to be at the hospital, and 6 or more processes to be completed daily.

However, due to frequent breakdowns, Hygiene Solutions struggled to meet their obligations, and on occasion asked engineers to put a non-functional Deprox unit in a room, tape up the door and “run” a process – thus not only defrauding the NHS but leaving a dangerously contaminated room that the staff believed to have been sterilized.

Plotting the contract dates against the quarterly UCLH C. difficile data² (extended through 2016 with mandatory government reporting data)³  reveals an exact correlation between the period of Deprox deployment and a substantial step change in the number of C.difficile infections  – approximately 70 extra cases over the 29 month period.

According to the March 2016 government report on C. difficile mortality, the 30 day mortality rates for the London area were about 17%. –  suggesting that approximately 12 deaths in this period could be attributed to Deprox operations. Any patients who acquired C. difficile or any other Heathcare Associated Infection, (HAI) in the UCLH hospitals between June 2013 and October 2015 should consider contacting a medical negligence solicitor and seeking compensation.

Deprox pushed UCLH in to high risk category for C. diff – CQC reports.

The CQC (Care Quality Commission) makes regular evaluations of NHS trusts using a list of critical indicators. These are the Intelligent Monitoring reports. The extracts from a series of these reports below show how the “Incidence of C. difficile” indicator moved from “No evidence of risk” to “Elevated Risk” when the Deprox program was implemented. The complete reports can be found at:

Deprox UCLH

[1]  (See graph, p.17)