Healthcare Surface Biofilms and Chlorine Dioxide: Reading the 2025 Journal of Hospital Infection Study

Why surface biofilm matters in healthcare

Healthcare surfaces are not clean stainless steel in a test rig. Bed frames, mattresses, commodes, blood-pressure cuffs, keyboards and sink surrounds carry soil, moisture cycles and repeated touch, and organisms such as meticillin-resistant Staphylococcus aureus, vancomycin-resistant enterococci, carbapenemase-producing Enterobacterales, multidrug-resistant Acinetobacter baumannii and the yeast Candidozyma (formerly Candida) auris can persist on them for weeks. Where they persist as biofilm, they are shielded by extracellular polymeric substance, include slow-growing persister cells, and can exchange resistance genes. A patient admitted to a room whose previous occupant carried an MDRO has a measurably higher risk of acquiring it, which is why environmental decontamination is a recognised infection-prevention control rather than housekeeping.

Biofilm also changes what a disinfectant test means. Standard efficacy tests (the EN 14885 family) use planktonic organisms or dried films on carriers; they are a legal and useful baseline, but a pass against a suspension is not a demonstration against an established biofilm.

The 2025 study: what was tested

Norville, Dangleben and Hardy published a short report in the Journal of Hospital Infection (volume 162, August 2025, pages 121-126; doi 10.1016/j.jhin.2025.04.034; open access). In the first part, several chlorine dioxide-based disinfectants at 150 to 200 ppm chlorine dioxide (a foam, a wiping solution and others) were tested to EN 13727, EN 14561, EN 16615 and EN 14562 against a panel of MDROs: VRE, carbapenem-resistant and ESBL-producing Klebsiella pneumoniae, MDR A. baumannii, MRSA and C. auris. All met the relevant standard's pass criteria within realistic contact times, generally with reductions greater than 4 to 6 log.

In the second part, 72-hour biofilms of Pseudomonas aeruginosa and Staphylococcus aureus were grown on the pegs of an MBEC (minimum biofilm eradication concentration) device following ASTM E2799 and exposed to the disinfectants for 30 seconds or 5 minutes, with a 10,000 ppm sodium hypochlorite positive control. The authors report that the chlorine dioxide products consistently achieved reductions of 4 log or more against both organisms, with larger reductions against P. aeruginosa (about 6 to 7 log, often to the detection limit) than against S. aureus (mean values of roughly 4 to 5.7 log, with the lower bounds of some products' error bars near 3.5 log). There was no statistically significant difference between 30 seconds and 5 minutes, and no significant difference between the chlorine dioxide products except one that also contained a quaternary ammonium compound. Six biological replicates were run per condition.

Affiliation, funding and limitations, stated plainly

Two of the three authors are employees of Tristel Solutions Limited, a manufacturer of chlorine dioxide disinfectants; the third is an independent infection-prevention consultant. All testing was funded by Tristel, and the products tested were Tristel formulations prepared to the manufacturer's instructions. The paper declares this openly. It does not invalidate the data, which were generated to recognised standards and published after peer review, but it means the study was designed and paid for by a party with a commercial interest in the outcome, and readers should weight it accordingly.

The authors themselves identify the main limitation: the MBEC assay is a rapid screening model with biofilm grown on plastic pegs in nutrient broth for 72 hours, and results against other biofilm models (such as the CDC reactor) or against real dry-surface biofilm with soil would be needed to extend the conclusion. The study also tested two laboratory reference strains in the biofilm model, not clinical MDRO isolates, used single-laboratory testing, and did not compare chlorine dioxide with other disinfectants at practical in-use concentrations; the only comparator was hypochlorite at 10,000 ppm, a concentration the authors note is unsuitable for routine use.

What this study does and does not establish

It establishes that, under EN test conditions, the chlorine dioxide formulations tested met the pass criteria against a clinically relevant MDRO panel including C. auris, and that in an MBEC screening model they achieved reductions the authors report as 4 log or more against 72-hour P. aeruginosa and S. aureus biofilm within 30 seconds. It is, according to the authors, the first report of chlorine dioxide performance in the MBEC model.

It does not establish the performance of chlorine dioxide in general, or of any product other than those tested. The concentrations, formulations, contact times and application methods in the paper belong to the products studied and must not be converted into instructions for ChloroKlean or any other product; a ChloroKlean product used on healthcare surfaces must be applied according to its own label and GB BPR authorisation for PT2, and any biofilm or MDRO claim must be supported by that product's own data. Nor does the study show that surface biofilm in a working ward would respond the same way as a 72-hour peg biofilm in broth. It is good evidence that the active substance deserves attention in healthcare decontamination strategies, which is the modest claim the authors make.

Where this fits in the UK framework

Disinfection of surfaces in healthcare settings falls under product-type 2 of the GB Biocidal Products Regulation. Products must be compliant for that use, whether authorised or lawfully supplied under transitional arrangements while chlorine dioxide is evaluated in the GB Review Programme. Infection-prevention teams work within national cleaning standards and their own decontamination policies; a published study informs product selection but does not replace the manufacturer's validated instructions, the trust's policy or local audit.

Evidence and uncertainty

Published biofilm studies are valuable for understanding mechanisms, but their conditions may not match a particular installation. Species, surfaces, deposits and operating conditions should be recorded when interpreting evidence.

For safety-critical systems, decisions should be documented through the relevant risk assessment and management plan.

Choosing the next question

A useful next step is to identify what is known, what is inferred and what needs verification. This avoids treating a general reference as a site diagnosis.

Where a product is considered, confirm the intended use, authorisation and label directions independently of this educational guide.

Use this sequence to frame investigation and control; it is not a dosing protocol.

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