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. http://sevron.co.uk/msds/deproxin-msds-download-2/[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

ultra-vfraud.info – a new editor, a new website launched.


A change of editor presents opportunity for a fresh approach. The extraordinary extent of Hygiene Solutions’ unscrupulous activities, ranging from misleading puffery to complex and ingenious corruption of “independent” scientific testing, generates a challenging volume and variety of data to present.

To simplify this task, I have launched a new website, www.ultra-vfraud.info, to expose Hygiene Solutions’  egregious lies as to their new Ultra-V product, while www.deproxfraud.info will concentrate on the Deprox scandal, now entering its final phase as the HSE investigation nears completion.

A recent “Freedom of Information” request has yielded some extraordinary data on Deprox efficacy. This independently verifiable dataset demonstrates a 25% increase in C. dificile incidence in a major UK NHS trust, correlated exactly to a 28 month period of intensive Deprox use. This will be published here shortly.

“Facts are stubborn things.”

John Adams, second President of America

The more the truth is tested and examined, the more firmly it stands. Lies, however credible at first glance, become shaky on close examination, and a determined investigation will reduce them to shreds and tatters. The mission of these websites is to present the facts, however unpalatable, about Hygiene Solutions Ltd, its criminally negligent directors and its dangerous and dishonestly promoted Deprox and Ultra-V products.

Dr Ecosse


“A despicable act.” – Judge Williams speaks out on NHS fraud.

Judge Adele Williams

Judge Adele Williams

Judgement was pronounced on a £26,000 NHS fraud last week. The perpetrators only escaped jail as they had pleaded guilty at the earliest opportunity and had repaid the money in full.

But Judge Adele Williams described it as a

” – mean, thoroughly dishonest and cynical fraud.”

She said further: –

“To deprive the NHS even indirectly of cash and funds when it is hard-pressed and needs every penny available is a despicable act.”

What would the Judge have to say to the perpetrators of an £8,000,000 fraud against the NHS? Even if the directors of Hygiene Solutions were to refund the NHS for the tens of thousands of fraudulent Deprox processes they have done over the years, (see https://deproxfraud.info/2017/03/13/leaked-emails-prove-test-cheating-bodily-harm-and-massive-fraud/ )  would they escape jail?

The following comment was received from a retired NHS nurse today…
“Rick F should be forced to make reparation on top of all due penalties. I suggest that he should, after being found guilty of fraud, be forced to attend the next infection prevention conference, with patient groups invited to give family impact statements in cases where relatives have become infected when Deprox has been in house. What the nurses would like to do with him I will leave to your imagination.”

Deprox fails log 6 test even in tiny test chamber.


deprox box

Hygiene Solutions claim a single Deprox unit has the capacity to decontaminate rooms with a volume of 380m3, e.g. a 12 bed ward bay. A typical hospital side ward (single room with ensuite) has a volume of 60m3.

However, the chamber used by Hygiene Solutions Ltd  to test the Deprox is 1.5m x 1.5m x 2.8m. Total volume 6.3m3 , just 10% of the volume of a hospital single bedroom, and 1.7% of the maximum volume that Deprox is guaranteed to disinfect. It is barely larger than a telephone box.

Hygiene Solutions internal testing, published here for the first time reveals that the Deprox, in spite of being boosted with 50% more concentrated hydrogen peroxide solution than the standard “Deproxin” was incapable of a log 6 decontamination of even this tiny test chamber.

The Deprox was thoroughly tested over a period of months by David Sempere Aracil, a well qualified chemist. David placed Log 6 biological indicator discs (Apex Biological Indicator #HMV-091) in 8 different locations around the inside walls of the test chamber. The Deprox unit (“Trusted by leading hospitals around the world”) was sealed in the chamber, and the process was run. The log6 BIs were incubated – they were all alive.

David tried substituting Sanosil SO15 which at 7.5% H2O2 is 50% more concentrated than Deproxin. Now some of the BIs would be sterilised, sometimes. Over several weeks in late 2014, David did a series of 12 tests in the test chamber, all with 7.5% H2O2 rather than the 5% Deproxin. He tried turning the ΔRH up and down, but to no avail. In 5 of these tests, all 8 BIs remained viable. None of the tests sterilised more than 6 out of 8.


In summary then:

Deprox, running on a 5% H2O2 solution, is claimed to give a log6 decontamination of an entire 380m3 ward, including inside small crevices and complex equipment. In Hygiene Solutions’ own tests, the Deprox running on a 7.5% solution, and thus generating a 50% higher aerial H2O2 concentration than the standard process, completely failed to give a log6 decontamination of a 6.3m3 box in multiple tests.

Hygiene Solutions continued to promote and sell the Deprox with exactly the same claims, but in 2015, they turned the whole Deprox fleet down from ΔRH20 to ΔRH5. See https://deproxfraud.info/2017/03/13/leaked-emails-prove-test-cheating-bodily-harm-and-massive-fraud/

Fortunately, (or unfortunately for Hygiene Solutions) David’s notes of these tests survived.


Explanation of table.

This table is a summary of 15 tests done by David Sempere Aracil, assisted by Tautvydas Karitonas, over a period of months. Both are university graduates with extensive research experience, and David has a PhD in Chemistry. The tests were done with a standard production model Deprox machine, the purpose of the tests was to determine if the extremely low efficacy of the Deprox process could be rectified by increasing the concentration of the hydrogen peroxide solution from the standard 5% to 7.5%.

The results were recorded in 3 A4 hardcover notebooks. Each of the 15 tests was recorded in more detail on preceding pages of the notebook. In addition to the efficacy tests, the notebooks contain extensive details of tests on prototype catalyst systems, and constitute proof that HS was well aware of both the low efficacy and residual gas issues with Deprox.

Heading: “Sanosil 015 forte” refers to Sanosil S015, which is a disinfectant intended for water systems. It is 7.5% Hydrogen peroxide solution. Note that this is more concentrated than the 5% Deproxin solution that is used in production Deprox machines.

Col.1. The test number. These are not sequential, as some tests did not use Biological indicators (BIs) and were not recorded in this resume.

Col. 2 Duration of test measured from when the machine starts vapourising. (It takes several minutes for the machine to fill the piezo tank at the beginning of each test)

Col. 3 Delta HR setting of machine. This is adjusted by using unmarked pressure sensitive switches below the LCD display. – see How to test your Deprox.

Col. 4 HRO This is the original relative humidity in the test chamber before the machine starts.

Col. 5 TO Temperature in the chamber before the machine starts

Col. 6 CMAX Hydrogen peroxide concentration in PPM, maximum level reached during process.

Results columns. The first 12 tests were done in the test chamber (wardrobe). Each number represents a specific marked location on the test chamber wall where an exposed stainless steel Bacillus subtilis log6 biological indicator was placed. The chamber is a crude wood and plasterboard structure in an essentially unheated warehouse. It is approximately 5’ x 5’ x 9’ and the indicators were placed at various heights on the interior walls of the chamber. The last 3 tests were done in the company board room which is approximately 12’ x 25’.

A” +” indicates that the BI still contained viable bacteria, a “–“ indicates that all bacteria on this indicator were killed.

Final column. This is the percentage of BIs that were killed.

Welsh Health Board suspends Deprox in all of its hospitals!

Dim Deprox

A major Welsh health board, with more than ten hospitals has suspended both Deprox and Ultra-V in all of its sites. The suspension is in response to numerous incidents of healthcare workers being exposed to high levels of toxic Deproxin fumes on re-entering a room after decontamination. Affected staff have been given a precautionary medical examination.

The RH (i.e. the amount of hydrogen peroxide in the air) of these machines was set to 13, where according to the manufacturer, a level of RH 40 is needed to give a log6 disinfection. This would account for reports of persistent contamination in some units in spite of repeated Deprox use. (You can easily find the RH setting of your Deprox here.)

Even with the machines turned down to almost a quarter of the required concentration, the level of H2O2 at the end of the process was so high that in many cases there was still a clearly visible fog in the air – and these incidents occurred AFTER Hygiene Solutions had fitted a catalyst to all its Deprox units in response to the serious accident in the Royal Worcester Hospital. This is further proof that the catalyst is just a placebo, to hide the fact that the ONLY way to ensure a safe atmosphere after a Deprox process is to turn down the H2O2 levels to 1/8th of the level needed for disinfection.

A similar problem was encountered by the Cwm Taf University Health Board, which covers the North Glamorgan area. They were sent a Deprox that had accidentally been set to RH 20, leaving the ward filled with a choking fog of chemicals after the “green light” had illuminated, indicating that the room was safe to enter. The Health Board used gas detector guns to measure residual hydrogen peroxide left after the process and it was 15 times the safe limit.

It should be pointed out that the Deprox machine has NO MEANS WHATEVER of monitoring the deactivation process. The green light is simply on a 45 minute timer, and will illuminate at this time regardless of the level of gas in the room.

Hydrogen peroxide gas detectors are expensive to buy, but can be rented at very reasonable rates from Drager UK.  The best detector for this application is the Drager X-am 5100. The contact number for gas detection enquiries is 01670 352891.

Note: Do NOT rely on on gas detectors supplied from Hygiene Solutions – these are calibrated to show only a fraction of the real gas level! This can very easily be demonstrated by using a HS supplied unit and a rented Drager unit side by side.

In the face of mounting evidence as to the grave danger this process poses to both healthcare workers and patients, it would seem a wise move to discontinue the use of this equipment until the official HSE enquiry has made its recommendations.

Cystic Fibrosis scam + new data from New Zealand.


Papworth Hospital, famous for its pioneering heart and lung transplants, is home to the Adult Cystic Fibrosis Centre, caring for around 330 sufferers of this terminal lung disease.  Infection control is of the utmost importance in Cystic Fibrosis wards, as the patient’s lungs are profoundly compromised and unable to reject infectious agents. Tragically, Papworth has been targeted by Rick Fentiman and his heartless minions.

Warned in advance of extensive microbiological testing (Hygiene Solutions cultivate inside contacts for this purpose) Tom Lister here requests the Deprox units to be turned up to RH30 (i.e.the highest possible aerial H2O2 concentration possible) – to ensure that the microbiological swabs demonstrate some meaningful reduction in bacterial load.

(Reminder – a full 6 log efficacy requires at least RH40. Legal gas levels at the end of a process can only be guaranteed at RH5)

  • Why then are the machines not already set at this level? Because at RH30 the residual H2O2 and AgNO3 after the process will be as much as 50 times the legal limit.
  • How do they get away with it? H2O2 is odourless, and  Papworth Hospital does not use H2O2 detectors.
  • Who suffers? The Cystic Fibrosis patients, whose fragile lungs can only just sustain life, are left to breathe the noxious chemicals.

Tom Lister Deprox fraud

If Hygiene Solutions should claim that RH30 is safe, they will have to explain this email, send 3 weeks later…

Mark Fentiman Deprox Cystic fibrosis

Just one month after this, Mark Fentiman sent an urgent message that all Deprox units were to be turned down to RH5. Now it emerges that this order was in response to the incident below, in which a healthcare worker at the Royal Worcester Hospital inhaled residual Deproxin fumes after the Deprox control unit had declared the room safe to re-enter, and suffered serious respiratory problems. (Note that ISS Healthcare operate the Deprox machines as a subcontractor in some NHS hospitals.)

Maria Cardoso

The Log6 claim so loudly and insistently trumpeted by Hygiene Solutions is based on a machine set to RH40. The RH setting gives the amount of H2O2 per cubic metre of air, so resetting the machine to RH5 only gives 12% of the required concentration. In reality, the machine is just a placebo – no useful or meaningful level of disinfection is possible at this level.

RH5% email Mark Fentiman

Tom Lister Deprox fraud

The shocking fact is that Hygiene Solutions continued to provide their Deprox systems and “decontamination” service at this dangerous and utterly ineffective level, did not inform their 60 or so NHS Hospital customers of the change, and continued to charge full price, a tidy sum of £2,500,000 per year.

Given that approximately 5000 NHS patients die each year from the very infections that this system is supposed to prevent, there can be no doubt that this action led to completely avoidable infections and death, as well as robbing the NHS of millions of pounds in fees for thousands of imaginary decontamination services that never actually took place.

5% image

This is not a historic problem – Deprox units at St James’s Leeds, Luton & Dunstable and Royal Liverpool hospitals are still set to RH5 and most other units, including Westmead Hospital in Sydney are at RH10. The Deprox is physically incapable of simultaneously giving a level of disinfection in excess of 1 log, and leaving a safe atmosphere at the end of the process. The label here, evidently peeled off one of the fleet machines, shows RH5 in July 2016. This proves that the emergency addition of a token catalyst in 2015 was completely ineffective.

While some hospitals, such as St James’s in Leeds used the Deprox in addition to a conventional hypochlorite (bleach) terminal clean, others have used Deprox instead. In other words, the introduction of Deprox has displaced an effective conventional cleaning protocol, and substituted a cleaning machine that is effectively turned off. Hygiene Solutions promotes what they call a RAG chart, grading the level of cleaning needed into Red, Amber and Green levels. The Red level is for terminal cleans of heavily contaminated side wards that have been occupied by a “superbug” patient. Thus the most ineffective cleaning method is applied to the most dangerous situations.

This can be seen from the following chart from North Shore Hospital, Waitemata DHB, New Zealand. It is obvious that the Deproxed rooms do not receive a conventional clean – they just have a “pre-clean” i.e removing soft furnishings, obvious gross decontamination etc. The “level one” chlorine based clean is much more effective than a Deprox set at RH5. How many New  Zealand patients have died as a result of this shocking fact we can only speculate…

waitemata north shore

Note: Deprox in New Zealand is promoted by Fort Richard Laboratories in Auckland.

If you are a Deprox user, you can easily check the RH level by following the instructions here:


If you have information about Hygiene Solutions Ltd, Deprox or Ultra-V, please contact HSE inspector, Mr. Martin Ball who is heading up the investigation, and quote CRD Ref: 2016022