This page provides an independent statistical analysis and educational interpretation of publicly reported results. ClinicalTrials.gov provides the official trial registry record. Numerical trial results on this page are restricted to the results posted in the ClinicalTrials.gov record; calculations added by Clinical Biostats are labelled as such.
1. Trial at a Glance
This page covers the registry results for Effect of Photodynamic Treatment on Skin Microbiome. Single Center Study (NCT04067843), a na na study. The primary outcome is Number of Participants With Bacterial Growth Before and After Photodynamic Treatment and After Skin Antisepsis.
| Feature | Registry value |
|---|---|
| ClinicalTrials.gov identifier | NCT04067843 |
| Phase | NA |
| Condition | Postoperative Wound Infection Deep Incisional Surgical Site, Prosthesis and Implants, Surgical Site Infection |
| Allocation | Not applicable (single group) |
| Design model | Single Group |
| Masking | None (open label) |
| Enrollment | 20 |
| Arms in the primary outcome | n/a |
| Lead sponsor | University of Zurich |
| Results posted | Yes |
2. Clinical Question
Population
The study concerns human inguinal skin and bacterial skin colonization. The registry record lists an enrollment of 20 participants and identifies postoperative wound infection, surgical site infection, prosthetic joint infection, and prostheses and implants among the conditions of interest. Participant characteristics and eligibility criteria are not reported in the registry record.
Intervention
The intervention is photodynamic treatment, recorded as a procedure. The study description focuses on skin microbiome observations before treatment, after treatment, and after skin antisepsis. Treatment details, including the procedure's specific parameters, are not reported in the registry record.
Comparator
The registered study model is single group, and allocation is listed as NA. The adverse-event record includes an entry labeled Control Group, but the registry record cautions that the arms are not a like-for-like control comparison. A valid controlled treatment contrast is therefore not established by these details.
Primary question
The primary endpoint asks how many participants have bacterial growth at the recorded sampling stages: before photodynamic treatment, after photodynamic treatment, and after skin antisepsis. The samples are skin swabs evaluated for bacterial growth on agar plates. The registry record does not report the counts at those stages, so it does not establish the size or direction of any change.
The broader stated aim is to investigate whether photodynamic therapy affects bacterial skin colonization, including bacteria associated with sebaceous and sweat glands, as part of research intended to inform skin antisepsis strategies. This is a microbiological question about skin samples. It is not a direct test of whether the procedure prevents surgical site infections or implant-associated infections. Those clinical outcomes are not reported as primary results in the registry record.
3. Trial Design
This is a completed, single-center pilot study sponsored by the University of Zurich. The registry record lists a planned enrollment of 20 participants, a start date of 2019-09-26, and a primary completion date of 2019-12-16. The study phase is listed as NA. The recorded intervention is photodynamic treatment, and the registered model is single group. Allocation is listed as NA, and masking is listed as NONE.
The planned observations center on skin microbiome samples taken before photodynamic treatment, after photodynamic treatment, and after skin antisepsis. The primary endpoint is the number of participants with bacterial growth at these stages, with sampling described for Day 1. This sequence of measurements can be used to describe bacterial growth across stages within the study. However, the registry record does not report the stage-specific counts or explain how paired observations were analyzed.
The adverse-event record contains entries labeled Photodynamic Treatment and Control Group, each listing 10 participants at risk. Those entries do not make the study a randomized or otherwise like-for-like comparison. The registry record expressly identifies the trial as not a randomized comparison and cautions that its arms are not a like-for-like control comparison. The single-group model should therefore guide interpretation of the study design; the adverse-event labels should not be treated as evidence of a controlled efficacy design.
Phylogenetic comparisons of isolated bacteria are listed as a secondary outcome. Three outcome measures are recorded, but the outcome details and results beyond the primary endpoint description are not reported in the registry record. No statistical analyses are listed. Details about eligibility, participant flow, the analysis population, treatment delivery, sample handling, and the statistical plan are not reported in the registry record. The sample-size justification is also not reported in the registry record.
4. Participant Flow and Accounting
The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.
Overall Study
| Stage | Photodynamic Treatment | Control Group |
|---|---|---|
| STARTED | 10 | 10 |
| COMPLETED | 10 | 10 |
| NOT COMPLETED | 0 | 0 |
5. Baseline Characteristics
The table reproduces the baseline characteristics posted in the registry, which describe the participants analysed at baseline and help show whether the randomized groups were comparable.
| Characteristic | Unit | Photodynamic Treatment | Control Group | Total |
|---|---|---|---|---|
| Participants analysed | 10 | 10 | 20 | |
| Age, Categorical: <=18 years | Participants | 0 | 0 | 0 |
| Age, Categorical: Between 18 and 65 years | Participants | 10 | 10 | 20 |
| Age, Categorical: >=65 years | Participants | 0 | 0 | 0 |
| Sex: Female, Male: Female | Participants | 5 | 7 | 12 |
| Sex: Female, Male: Male | Participants | 5 | 3 | 8 |
| Race and Ethnicity Not Collected | Participants | — | — | 0 |
| Region of Enrollment: Switzerland | Participants | 10 | 10 | 20 |
6. Primary Endpoint
The registry lists the primary outcome as Number of Participants With Bacterial Growth Before and After Photodynamic Treatment and After Skin Antisepsis, measured over Day 1.
| Element | Registry entry |
|---|---|
| Result type | Count Of Participants |
| Measure of spread | not applicable |
| Unit | Participants |
| Endpoint classification | Binary Endpoint |
The primary endpoint is the number of participants with bacterial growth on agar plates from skin swabs taken before photodynamic treatment, after photodynamic treatment, and after skin antisepsis. It is recorded as a count of participants, with Day 1 given as the timeframe. This endpoint turns a microbiological observation into a participant-level summary: a participant is counted according to whether bacterial growth was observed at a sampling stage. The registry record does not further define the threshold or rule used to classify growth.
Repeated sampling around the treatment and antisepsis stages can describe whether observed growth differs across those stages in the studied group. Such measurements may be relevant to the stated research aim of examining bacterial colonization and antiseptic strategies. They do not, by themselves, measure infections after surgery, implant-associated infection, or prevention of those clinical outcomes. The primary endpoint is a microbiological surrogate observation, not a clinical infection endpoint.
The registry record does not report how many participants had bacterial growth at any stage, how many samples were evaluable, or how missing or indeterminate samples were handled. It also does not report a statistical estimate of change or uncertainty around the counts. Consequently, the endpoint's recorded definition can be described, but its observed result and precision cannot be assessed from the registry record.
7. Why No Re-analysis Is Shown
8. Statistical Interpretation
The registry record identifies a clear sequence of microbiological assessments: skin swabs before photodynamic treatment, after treatment, and after skin antisepsis, with bacterial growth evaluated on agar plates. It also identifies the primary endpoint as the number of participants with bacterial growth. These details establish what the endpoint was intended to capture, but not what was observed. The number of participants with growth at each stage is not reported in the registry record.
There is therefore no posted primary outcome estimate to interpret. No stage-specific counts, differences, confidence intervals, p-values, or statistical analyses are reported in the registry record. Without the observed counts, the direction and magnitude of any change in bacterial growth cannot be described. Without an uncertainty estimate, the precision of any potential change also cannot be assessed. The completed status and enrollment of 20 do not substitute for endpoint results.
The design also limits what a comparison could establish. The registered model is single group, allocation is NA, and the registry record cautions that the labeled arms are not a like-for-like control comparison. A before-and-after sequence may describe observations within participants, if paired data were collected and analyzed, but the details of such an analysis are not reported. Even a change between sampling stages would not automatically isolate the effect of photodynamic treatment from other influences, including the later antisepsis stage. The registry record does not report an analysis that separates these effects.
The primary outcome is bacterial growth on agar plates, not a count of surgical site infections or implant-associated infections. The study's stated motivation relates to infection prevention, but the recorded primary endpoint does not directly establish whether clinical infections occurred or were prevented. The secondary outcome of phylogenetic comparisons of isolated bacteria is listed, but results are not reported in the registry record.
Safety entries list zero serious adverse events, zero other adverse events, and zero deaths for the Photodynamic Treatment and Control Group records. Each entry lists 10 participants at risk. These figures describe the adverse-event record as registered; they do not resolve the absence of outcome details, participant flow, or a valid control comparison. In particular, zero events recorded in those entries should not be read as proof that no adverse events occurred among all participants or that the intervention is free of risk.
Overall, the registry record supports a description of the study question and sampling sequence, but not a quantitative conclusion about the microbiological endpoint, its precision, or a clinical benefit. Those results are not reported in the registry record.
9. Statistical Methods Explained
The statistical methods that were actually used are not reported in the registry record. No analyses are listed, and the primary endpoint results are absent. The following explains the concepts relevant to interpreting the design and endpoint; it does not describe a confirmed analysis plan for this study.
What a participant count can describe
The primary endpoint is a count of participants with bacterial growth. At each sampling stage, that count would describe how many participants met the endpoint definition at that stage. It is a binary outcome at the participant level: growth is either recorded or not recorded according to the study's classification. The registry record does not define the classification threshold or provide the actual stage-specific counts.
For repeated observations on the same people, comparisons across stages are paired in nature. The observations from one person may be related because they come from the same person. A suitable analysis would need to account for this relationship rather than treating all stage-specific observations as independent. Which method, if any, was used is not reported in the registry record. The record also does not say how incomplete sets of swabs were handled.
How uncertainty would be expressed
In general, a confidence interval describes a range of values compatible with the data under a specified statistical method. It communicates uncertainty around an estimate; it is not a guarantee that the true value lies in that range. For participant counts or proportions, uncertainty depends on the observed data and the method used. No confidence interval or other uncertainty estimate for the primary endpoint is reported in the registry record, so the precision of an observed change cannot be judged.
In general, a p-value addresses how compatible observed data are with a specified null hypothesis under a statistical model. It does not measure the size or clinical importance of an effect, nor does it repair weaknesses in study design. No p-value or hypothesis test is reported in the registry record. Because the primary results are also absent, a test result cannot be reconstructed or interpreted from the endpoint description alone.
Why the design matters
The registered model is single group, with allocation listed as NA. Measurements before and after treatment can be informative descriptions, but a comparison across time does not by itself establish that the intervention caused a difference. Other changes between sampling stages, including the stated antisepsis procedure, may also affect the observations. A concurrent, comparable control group can help distinguish intervention effects from other influences, but the registry record says its labeled arms are not a like-for-like control comparison. The registry record does not report a design or analysis that resolves this limitation.
In general, random allocation helps balance known and unknown prognostic factors across treatment groups, on average. This study is not registered as a randomized comparison. It would therefore be inappropriate to interpret the adverse-event labels as proof of randomized allocation or to use them to claim a controlled treatment effect. The study's single-group model and the explicit caution about the arms are more relevant to the interpretation.
Planning calculations and observed results
The registry record describes a sample-size planning illustration based on an observed effect, with a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. It says that the effect to detect is a stated fraction of the observed effect. Such calculations are planning illustrations, not observed power and not evidence that an effect was found. The calculated participant counts are not reported in the registry record, and the underlying observed effect is also not reported. The trial's own sample-size justification is not reported in the registry record.
In general, power is a design-stage probability of detecting a specified effect under stated assumptions if that effect exists. It is not a retrospective measure of whether a study result is true. Planning illustrations based on an observed effect can be especially uncertain when the underlying estimate is imprecise. Since the registry record supplies neither an observed endpoint estimate nor calculated planning counts, no numeric sample-size inference can be drawn.
Analyses and multiplicity
Three outcome measures are recorded, and phylogenetic comparisons of isolated bacteria are listed as a secondary outcome. The specific analyses and any adjustment for testing multiple outcomes are not reported in the registry record. In general, when multiple hypotheses are tested, the chance of at least one apparently notable result can increase unless the analysis plan accounts for multiplicity. The record does not say whether multiple tests were planned or how any such issue was handled. No conclusion about statistical significance or multiplicity-adjusted inference can be made.
Overall, the registry record provides an endpoint definition and broad design information but not the analysis methods or results needed for statistical assessment. The explanations above are general statistical context, not claims about methods that were used in this study.
10. Multiplicity, Missing Data and Analysis Populations
Three outcome measures are recorded, and phylogenetic comparisons of isolated bacteria are listed as a secondary outcome. The registry record does not report the full outcome definitions, which outcomes were analyzed, whether any hypotheses were prespecified, or how multiple comparisons were handled. In general, testing multiple outcomes can raise the chance of obtaining an apparently notable result by chance. Statistical approaches can address that issue, but the analysis plan and any multiplicity adjustment are not reported in the registry record. No inference about adjusted or unadjusted significance is available.
Missing-data handling is not reported in the registry record. There is no reported account of how many participants contributed evaluable swabs at each stage, whether samples were missing or unusable, or how missing observations were treated. These details matter because an analysis of only participants with complete samples can differ from an analysis that includes all enrolled participants under an explicit missing-data method. The registry record does not identify which approach, if any, was taken.
The analysis population is also not reported in the registry record. There is no description of whether analyses included all enrolled participants, only participants who received the procedure, or a subset with available microbiological measurements. Participant flow and exclusions from analysis are not reported. The registered enrollment of 20 alone does not establish how many participants were included in any endpoint analysis.
No statistical analyses are listed. Accordingly, the record does not establish how the primary endpoint, secondary outcome, missing data, or multiplicity were handled. These absences limit the ability to assess both the validity and the precision of any potential result.
11. Safety Results
The registry reports serious adverse events as affected participants divided by participants at risk.
| Arm | Participants with serious adverse events | Participants at risk | Percentage |
|---|---|---|---|
| Photodynamic Treatment | 0 | 10 | 0.0% |
| Control Group | 0 | 10 | 0.0% |
Deaths
| Arm | Deaths (participants affected of at risk) |
|---|---|
| Photodynamic Treatment | 0 of 10 |
| Control Group | 0 of 10 |
Other (non-serious) adverse events
Participants with at least one non-serious event at or above the registry's 0% reporting threshold.
| Arm | Participants affected of at risk |
|---|---|
| Photodynamic Treatment | 0 of 10 |
| Control Group | 0 of 10 |
The adverse-event record has separate entries labeled Photodynamic Treatment and Control Group. Each lists 10 participants at risk, zero serious adverse events, zero other adverse events, and zero deaths. These are the figures recorded for those entries; the registry record does not provide event details or a narrative safety analysis.
The labels do not establish a like-for-like safety comparison. The study model is single group, and the registry record cautions that it is not a randomized comparison and that the arms are not comparable as controls. It would therefore be misleading to interpret the two entries as evidence from a valid comparative safety design.
Zero recorded events should be read narrowly: no events are listed in these registry entries. The record does not report how adverse events were collected, the observation period for safety, whether all participants were assessed, or whether events were coded or summarized using additional categories. It also does not report participant-level safety data. These omissions mean that the entries cannot establish the absence of risk. They describe the posted adverse-event figures, not a complete account of safety or a comparison of treatment risks.
12. What the Result Does, and Does Not, Mean
The registry record documents a pilot investigation of photodynamic treatment in relation to bacterial skin colonization and antisepsis. Its primary endpoint concerns bacterial growth on agar plates from skin swabs taken before treatment, after treatment, and after skin antisepsis. The record also lists phylogenetic comparisons of isolated bacteria as a secondary outcome. These details identify the subject and intended measurement of the study.
The record does not report the primary endpoint counts, any effect estimate, or uncertainty around an estimate. It therefore cannot show whether bacterial growth changed across the sampling stages, how large any change was, or how precisely it was estimated. Statistical analyses are not listed, and the secondary outcome results are not reported in the registry record. The study's completed status does not fill those gaps.
The design information also constrains interpretation. The registered model is single group, and the registry record states that this is not a randomized comparison and that the arms are not a like-for-like control comparison. Any within-study change across sampling stages, if observed, would not alone establish that photodynamic treatment caused it. The record does not report a design or analysis that separates treatment from the effects of other events in the sampling sequence, including antisepsis.
The outcome is microbiological rather than clinical. The stated motivation concerns strategies to prevent surgical site and implant-associated infections, but the primary endpoint does not directly measure those infections. The registry record does not report clinical infection results or evidence that the microbiological endpoint predicts those outcomes.
The safety entries list zero serious adverse events, zero other adverse events, and zero deaths for each labeled group, with 10 participants at risk in each entry. Those figures are limited to the posted record and should not be treated as proof of no harm. In sum, the registry record describes a pilot question and measurement approach but does not provide results sufficient to quantify an effect or draw a clinical conclusion.
13. Why This Trial Matters Statistically
This study raises a useful statistical distinction between measuring a biological process and demonstrating a clinical outcome. Bacterial growth from skin swabs can characterize microbiological observations across treatment and antisepsis stages. It is not the same endpoint as a surgical site infection or an implant-associated infection. Keeping those outcomes distinct prevents a surrogate measurement from being overstated as evidence about clinical prevention.
The design highlights why the structure of a comparison matters. Repeated observations in one group can describe changes over a sequence, but such a pattern is not equivalent to a randomized comparison. The registry record identifies a single-group model and specifically warns that the labeled arms are not a like-for-like control comparison. This makes it important to distinguish descriptive change from a causal treatment effect.
The record also illustrates how endpoint definitions and results serve different purposes. It describes the sampling stages and the participant-level bacterial-growth outcome, yet does not report the corresponding counts or analyses. Without those results, neither the direction of a change nor its precision can be assessed. A clear endpoint definition is necessary for interpretation, but it cannot substitute for observed data.
Finally, the pilot context does not remove the need for transparent reporting of participant flow, missing samples, analysis populations, and statistical methods. Those details are not reported in the registry record. Their absence limits reproducibility and makes it difficult to judge how robust any eventual estimate might be. The record is therefore most informative as a description of the research question and design constraints, rather than as quantitative evidence about treatment effects.
14. Limitations
- The posted summary statistics are the only data these results rest on; patient-level data, full protocols and statistical analysis plans are not available.
- Recalculated results are simple, unadjusted calculations from posted summaries. They do not replace the sponsor's prespecified analysis.
Several limitations are specific to the information recorded for this study. First, the primary endpoint is described, but its observed counts at the sampling stages are not reported in the registry record. Without those counts, the size, direction, and precision of any change cannot be assessed. No statistical analyses are listed, and no effect estimates, confidence intervals, or p-values are reported.
Second, the registered design is single group, with allocation listed as NA. The registry record explicitly states that the study is not a randomized comparison and that the labeled arms are not a like-for-like control comparison. The adverse-event entry for a Control Group should therefore not be treated as evidence of a valid control arm for evaluating efficacy.
Third, the endpoint is bacterial growth from skin swabs, not a clinical infection outcome. The broader stated aim concerns strategies for preventing surgical site and implant-associated infections, but the registry record does not report results for those clinical outcomes. The relationship between the microbiological endpoint and clinical outcomes is not reported in the registry record.
Further details needed to assess the study are not reported in the registry record. These include eligibility criteria, participant characteristics, the number of evaluable samples at each stage, missing-data handling, participant flow, the analysis population, procedure details, and the statistical analysis plan. The record also does not report the sample-size justification or the results of the listed secondary outcome. Together, these gaps prevent a fuller assessment of both the study's internal validity and the precision of its findings.
15. Related Tutorials
16. Related Statistical Calculators
17. Sources
- ClinicalTrials.gov: Effect of Photodynamic Treatment on Skin Microbiome. Single Center Study — NCT04067843.
- Registry record last updated 2022-05-18; status last verified 2022-03.
- Results first posted 2022-05-18.
- Data retrieved from ClinicalTrials.gov on 2026-11-09.
- Group sizes, means, event counts and sponsor-reported p-values are reproduced as posted. Effect estimates, confidence intervals and p-values not attributed to the sponsor are independently calculated from the posted summary statistics.
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18. Record Summary
The registry record describes a completed, single-center pilot study sponsored by the University of Zurich, with enrollment of 20 and a registered single-group model. The intervention is photodynamic treatment. The primary endpoint is the number of participants with bacterial growth on agar plates from skin swabs taken before treatment, after treatment, and after skin antisepsis, with Day 1 listed as the timeframe. Phylogenetic comparisons of isolated bacteria are listed as a secondary outcome.
The record does not report primary outcome counts, secondary outcome results, or statistical analyses. It identifies no randomized comparison and cautions that the treatment and control labels do not represent a like-for-like comparison. Adverse-event entries list zero serious adverse events, zero other adverse events, and zero deaths for both labeled groups, each with 10 participants at risk. The recorded information supports description of the study question and design, but not estimation of treatment effects or clinical conclusions.