Efficacy Study of Antiseptic Preoperative Scrubs in Prevention of Postoperative Infections: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Efficacy Study of Antiseptic Preoperative Scrubs in Prevention of Postoperative Infections (NCT00290290), a randomized phase 3 study. The primary outcome is The Primary Objective of This Trial is to Compare the Impact of Disinfecting the Skin With Chloraprep vs. Betadine on the Rates of Infection of Clean-contaminated Surgical Wounds..

2. Clinical Question

The clinical question is about the comparative infection outcomes associated with two antiseptic preparations in a particular surgical context. The registry frames the rationale around the possibility that reducing skin organisms could reduce wound infections. That rationale is not itself evidence about the relative effect of the two preparations; the trial outcome is the relevant comparison.

The registry also describes planned interest in skin adverse effects and cost-savings. However, the posted primary result concerns surgical-site infection, and no secondary outcomes are posted. The infection result therefore does not answer the additional questions about skin effects or costs.

3. Trial Design

The registry describes a phase 3, randomized, double-masked clinical trial sponsored by Baylor College of Medicine. It lists enrollment as 849 and the trial status as completed. The recorded start is 2003-09, and primary completion is recorded as 2008-05. These dates describe the registry record and do not, by themselves, provide details about recruitment duration or follow-up completion.

Two intervention arms are described: preoperative povidone-iodine preparation and preoperative chlorhexidine-alcohol preparation using a scrub-and-paint technique. The arm records list 440 for povidone-iodine and 409 for chlorhexidine-alcohol. These are the arm-specific values in the registry; the record does not explain whether they represent all randomized participants, participants with available primary outcome data, or another analysis population.

There is an internal design-label inconsistency. The registry identifies allocation as randomized and gives descriptions for two intervention arms, but its model field says single group. The record does not clarify that model label. The two-arm comparison is also explicit in the reported primary analysis, so the label should not be taken as a description that resolves the documented comparison.

The primary objective was to compare rates of infection of clean-contaminated surgical wounds. The endpoint was any surgical-site infection, diagnosed by a blinded reviewer. The description says efficacy was assessed by comparing proportions of evaluable patients with any infection and calculating a relative risk with a 95% confidence interval. It also states that consistency across the 6 participating hospitals was assessed using a prespecified Breslow-Day test for homogeneity.

Details about the randomization sequence, allocation concealment, which people were masked, and the exact analysis population are not reported in the registry record. The entry identifies the trial as double-masked but does not specify the masked roles. A detailed statistical analysis plan, including any changes made during conduct, is also not reported.

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.

Before assignment: There were no significant events prior to group assignment. Enrolled patients were immediately and randomly assigned in a 1:1 ratio to a study arm. To help match the two groups and address potential inter-hospital differences, randomization was stratified by hospital with the use of computer-generated randomization numbers without blocking

Overall Study

Reasons for not completing this period:

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.

6. Primary Endpoint

The registry lists the primary outcome as The Primary Objective of This Trial is to Compare the Impact of Disinfecting the Skin With Chloraprep vs. Betadine on the Rates of Infection of Clean-contaminated Surgical Wounds., measured over during surgery and within the 30 days post surgery.

The primary endpoint was the occurrence of any surgical-site infection. Its stated timeframe was during surgery and within the 30 days post surgery. Infection was diagnosed by a blinded reviewer following criteria developed by the Center for Disease Control. The registry gives the outcome unit as percentage of post-operative infections and describes the efficacy comparison in terms of proportions of evaluable patients with any infection.

An infection endpoint is relevant to the stated research question because the trial aimed to compare antiseptic skin preparations in relation to postoperative wound infection. Defining the outcome as any surgical-site infection makes the endpoint a binary event for each evaluated patient: infection was either recorded or was not. This framing supports a comparison of event proportions and a relative risk, as described in the record.

Blinded outcome review is relevant because assessment of infection can involve judgment. Having a reviewer unaware of treatment assignment can reduce the opportunity for knowledge of assignment to influence classification. The record does not give further details about the review process or the specific criteria used to classify each infection.

The timeframe defines which infections contribute to the primary endpoint, but it does not establish how patients with incomplete follow-up were handled. The registry does not report the number of patients whose infection status could not be evaluated or how missing outcome information was treated. The reported percentages should therefore be read alongside the unspecified analysis population and missing-data handling.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The registry describes several statistical procedures, each addressing a different aspect of the trial. The primary efficacy comparison concerns a binary outcome: whether an evaluated patient had any surgical-site infection. The record says the proportions in the two groups were compared using Fisher's exact test, and that a relative risk and 95% confidence interval were calculated. It separately lists the reported-analysis method as Log Rank. The record does not explain this difference in method labels.

What does a relative risk communicate?

A relative risk compares the probability of an event in one group with the probability in another. A value of 1 represents equal event probabilities. A value below 1 indicates a lower estimated event probability in the numerator group, relative to the reference group; a value above 1 indicates a higher estimated probability. Here, the reported comparison identifies povidone-iodine as the control and gives a relative risk of 0.59 for the comparison with chlorhexidine-alcohol. This is a relative measure, not an absolute difference in percentage points.

The confidence interval gives a range of estimates compatible with the observed data under the method's assumptions. Its width conveys precision: a narrower interval generally indicates greater precision than a wider interval. The reported 95% interval is 0.41 to 0.85. It describes uncertainty in the relative-risk estimate, not a range containing 95% of patient outcomes and not a guarantee about the true effect. Interpretation also depends on whether the stated analysis and population are appropriate.

Why use Fisher's exact test?

Fisher's exact test is a method for comparing categorical outcomes between groups. It evaluates how compatible the observed allocation of events and non-events is with a null hypothesis of no association, using the margins of the comparison. It can be useful when event counts are limited, because it does not rely on the same large-sample approximation used by some other tests. The registry says this test was used for efficacy proportions. The reported p-value is 0.004, but the entry does not give a detailed test specification or say whether any adjustments were made.

Why compare baseline characteristics?

The description says continuous patient characteristics were compared with the Wilcoxon rank-sum test and categorical characteristics with Fisher's exact test. The Wilcoxon rank-sum test compares the distributions of a continuous measurement between groups using the ordering of observations rather than requiring a normal-distribution model. Fisher's exact test is used for categorical characteristics. Such comparisons describe observed balance; they do not establish that randomization succeeded or failed, and baseline significance tests are not a substitute for understanding the allocation process. The individual baseline results are not reported in the registry record.

What does the hospital consistency test address?

The entry describes a prespecified Breslow-Day test for homogeneity across the 6 participating hospitals. In general, a homogeneity test asks whether an association or comparative effect is consistent across strata, rather than assuming the same effect in every stratum. The Breslow-Day approach assesses whether relative odds are homogeneous across strata. The registry describes the test as assessing consistency across hospitals, but it does not post the test statistic, p-value, hospital-specific estimates, or a detailed interpretation. The general purpose of such a test is to examine variation; a non-significant result would not prove identical effects, and a significant result would require attention to the pattern and precision of stratum-specific estimates.

How should the Log Rank label be read?

The reported analysis is labelled Log Rank, while the endpoint description says the efficacy outcome was compared as proportions using Fisher's exact test and a relative risk. A log-rank test is generally used to compare time-to-event distributions when event timing and censoring are part of the analysis. The endpoint is described as whether any infection occurred within a stated period, and no event-time estimates or censoring details are reported. The registry does not explain whether the Log Rank label refers to another implementation, a time-to-event analysis, or a recording issue. It is therefore important to report the label as recorded without assuming unreported details about the analysis.

These methods answer related but nonidentical questions. The relative risk describes the estimated relative event probability; the confidence interval expresses uncertainty in that estimate; and a hypothesis test assesses compatibility with a null model. None independently addresses clinical relevance, missing outcome information, or whether effects generalize beyond the trial population. Those questions require information about the participants, conduct, analysis population, and outcomes that the registry record does not fully report.

10. Analyses Reported by the Sponsor

The registry reports a relative risk of 0.59 for chlorhexidine-alcohol compared with povidone-iodine, a 95% confidence interval of 0.41 to 0.85, and p = 0.004. The arm entries report infection values of 16.1% for povidone-iodine and 9.5% for chlorhexidine-alcohol. These are the posted trial results and should be distinguished from any separate calculation based on summary statistics.

No separate recalculated estimate or recalculated confidence interval is reported in the registry record. The record marks the comparison as having no discrepancy, but it does not give additional recalculated values to compare with the reported analysis. Consequently, there is no independent numerical re-calculation to describe alongside the registry estimate.

The registry's own analysis is the primary source for the reported trial inference. The methods description says the efficacy proportions were compared using Fisher's exact test and a relative risk with a 95% confidence interval, while the reported-analysis entry labels its method Log Rank. The record does not reconcile those descriptions. That limitation concerns the available method documentation; it does not justify replacing the posted estimate with an unreported alternative.

The reported estimate can be interpreted in the stated group order, while keeping the method-label issue and the unspecified analysis population in view. Any planning illustrations based on an observed effect would be hypothetical design calculations, not observed power and not a substitute for the trial's reported analysis.

11. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome measure and one reported analysis, and it posts no secondary outcomes. The summary describes additional interests in skin adverse effects and cost-savings, but there are no posted secondary results for those questions. The absence of posted secondary outcomes means that multiplicity across a set of reported secondary efficacy tests cannot be evaluated from this record.

A multiplicity plan describes how inference is handled when multiple outcomes, time points, groups, or analyses are tested. The registry record does not report a broader testing hierarchy, a family-wise error approach, or another multiplicity adjustment. The fact that one primary outcome measure and one analysis are listed does not establish that there were no other analyses during the trial; those details are not reported in the registry record. The stated prespecified hospital homogeneity test is described, but its result is not posted.

The endpoint description says that efficacy proportions were compared among patients who could be evaluated. That wording identifies an evaluable-patient analysis, but the registry does not define the criteria for evaluability. It does not say whether the primary analysis followed intention-to-treat, per-protocol, or another population definition. The arm entries list 440 for povidone-iodine and 409 for chlorhexidine-alcohol, but the record does not establish whether these values are randomized group sizes, evaluable denominators, or both.

Missing-data handling is also not reported in the registry record. The number of patients with unknown infection status, reasons for missing outcome information, and any imputation or sensitivity analyses are not given. Without those details, it is not possible to determine from the registry whether missingness could have affected the estimated comparison or how robust the result is to alternative assumptions.

These omissions limit assessment of the analysis pathway, not just the numerical estimate. Randomization addresses group assignment, but it does not on its own resolve post-randomization exclusions, incomplete follow-up, or selective outcome reporting. The primary result is interpretable as posted, while its relation to a complete randomized population and to unreported analyses remains uncertain.

12. Safety Results

The registry reports serious adverse events as affected participants divided by participants at risk.

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0.7% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: death (1.0%).

The registry's serious adverse-event summary lists 3 affected participants among 440 at risk in the povidone-iodine group and 4 among 409 at risk in the chlorhexidine-alcohol group. These are the recorded counts and at-risk denominators. They should not be converted into a new comparative rate without an explicitly reported analysis and appropriate uncertainty assessment.

The serious adverse-event field lists Death as a top serious term at 1.0%. However, the arm-level deaths fields are null. The record therefore does not provide arm-specific death counts, and the term listing should not be used to infer how deaths were distributed between groups or to resolve the missing arm-level information.

The summary also records 3 other affected participants in each group, with the same arm-specific at-risk values shown for the serious-event summaries. The registry does not provide detailed event descriptions, timing, attribution, or statistical comparisons for these entries. It also does not provide enough information to determine whether the recorded serious events were considered related to the antiseptic.

These safety figures are descriptive registry entries. They do not establish a comparative safety profile, and the event counts should be read in light of the missing detail and the absence of a reported safety analysis. Skin adverse effects were among the trial's stated interests, but no secondary outcomes are posted for that question.

13. What the Result Does, and Does Not, Mean

The central statistical finding is a reported relative risk of 0.59 for surgical-site infection with chlorhexidine-alcohol compared with povidone-iodine. The 95% confidence interval is 0.41 to 0.85, and the reported p-value is 0.004. The arm-specific infection values are 9.5% for chlorhexidine-alcohol and 16.1% for povidone-iodine. Together, these posted values indicate that the estimated infection outcome was lower in the chlorhexidine-alcohol group in this trial's reported comparison, with uncertainty described by the confidence interval.

The result does not quantify every aspect of treatment choice. It does not report the costs associated with either preparation, and the registry contains no secondary results about skin effects. It does not establish how the comparison would apply in surgical settings other than clean-contaminated wounds, or in patient groups whose characteristics are not reported. Nor does the result answer questions about infection outcomes beyond the stated period of surgery and the 30 days post surgery.

The confidence interval and p-value are statistical summaries, not measures of the probability that a treatment will benefit a particular patient. They do not establish the practical importance of the difference in every setting. Interpretation requires considering the outcome definition, the trial population, the actual analysis population, and the quality of follow-up. The registry gives limited detail about the last two issues.

The stated randomized and double-masked design supports a comparative interpretation, but the design record is not fully coherent: it also labels the model single group despite documenting two intervention arms. The method label for the reported analysis differs from the efficacy-method description, and missing-data handling and analysis-population definitions are not reported. These limitations leave aspects of how the estimate was produced unresolved.

Accordingly, the result is evidence about the posted primary endpoint in the trial as recorded, not a universal statement about all antisepsis choices or all surgical-site infections. It should not be extended to unreported safety, cost, or secondary outcomes, and the numerical estimate should be understood with its stated confidence interval and the registry's methodological gaps.

14. Why This Trial Matters Statistically

This trial offers a useful statistical example because it reports both arm-specific infection values and a comparative relative-risk estimate with a confidence interval and p-value. Those summaries answer different questions. The arm values describe the observed endpoint within each group, while the relative risk expresses the comparison on a relative scale. The confidence interval communicates uncertainty in that comparison, and the p-value addresses compatibility with a null hypothesis under the reported test.

The trial also illustrates why endpoint definitions matter. Infection was defined as any surgical-site infection diagnosed by a blinded reviewer, with a specified follow-up window. A clear event definition and blinded assessment can help make group comparisons interpretable, especially when outcome classification involves judgment. At the same time, the record does not give detailed operational criteria or missing-data procedures, so the endpoint description cannot answer every question about measurement.

Several features call for careful reading rather than an automatic interpretation of a single result. The record describes a randomized two-arm comparison but carries a single-group model label. It describes Fisher's exact test for efficacy proportions but labels the reported analysis Log Rank. It also states that evaluable patients were compared without defining the evaluable population. These are distinct documentation issues, and none should be silently resolved by assumption.

The registry further shows the boundary between a stated research objective and posted evidence. The summary mentions skin effects and cost-savings, but no secondary outcomes are posted for those aims. Likewise, a planned test of consistency across hospitals is described, but its result is not reported. Statistical interpretation depends not only on what is reported, but on recognizing which parts of the research question remain unanswered in the registry.

For biostatisticians and clinical researchers, the example reinforces the value of reporting the analysis population, missing-data handling, test specification, subgroup or stratum results, and secondary outcomes. These details help readers assess precision, reproducibility, and applicability without conflating the reported estimate with a complete account of every trial question.

15. 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 trial. The registry identifies the intended population as patients undergoing clean-contaminated surgery, but gives no detailed eligibility criteria, operation types, patient characteristics, or baseline results. The applicability of the estimate to particular patient groups or procedures cannot be judged from the posted record alone.

The design fields are not fully aligned: randomization and two intervention arms are described, while the model is listed as single group. The record does not explain this classification. It identifies the trial as double-masked but does not say which participants, clinicians, assessors, or other personnel were masked, or how masking was maintained.

The primary analysis description refers to evaluable patients, but the criteria and population are not defined. The arm values are listed as 440 and 409; the registry does not clarify their relation to randomization, endpoint availability, or the primary comparison denominator. Missing outcome counts, reasons for missingness, and methods for handling missing data are not reported.

The efficacy description names Fisher's exact test and relative risk, whereas the reported-analysis method is labelled Log Rank. The record does not explain the difference or provide enough detail to determine precisely how the reported p-value was generated. The hospital homogeneity test is described as prespecified, but no result or hospital-specific estimate is posted.

Finally, the registry posts no secondary outcomes despite the summary's stated interest in adverse skin effects and cost-savings. The serious-event entries have limited detail, and arm-level death counts are null. These reporting gaps constrain interpretation of safety and other objectives as well as assessment of the primary analysis. They do not alter the values recorded for the primary comparison, but they limit how fully those values can be appraised.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: Efficacy Study of Antiseptic Preoperative Scrubs in Prevention of Postoperative Infections — NCT00290290.
• Registry record last updated 2014-09-18; status last verified 2014-09.
• Results first posted 2014-08-11.
• 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.

19. Record Summary

The registry describes NCT00290290 as a completed, phase 3, randomized, double-masked trial sponsored by Baylor College of Medicine. It compares preoperative chlorhexidine-alcohol preparation with povidone-iodine for clean-contaminated surgery. Enrollment is recorded as 849; the start is 2003-09 and primary completion is 2008-05.

The primary endpoint was any surgical-site infection during surgery and within the 30 days post surgery, diagnosed by a blinded reviewer. The posted arm values are 9.5% for chlorhexidine-alcohol and 16.1% for povidone-iodine. The reported relative risk is 0.59, with a 95% confidence interval of 0.41 to 0.85 and p = 0.004.

The record describes an evaluable-patient comparison, but does not define the analysis population or report missing-data handling. It also contains a single-group model label alongside the documented two-arm randomized comparison, and differing method descriptions for the primary analysis. No secondary outcomes are posted.