Surgical Site Infection With 0.05% Chlorhexidine (CHG) Compared to Triple Antibiotic Irrigation: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Surgical Site Infection With 0.05% Chlorhexidine (CHG) Compared to Triple Antibiotic Irrigation (NCT02395614), a randomized na study. The primary outcome is Number of Participants With Surgical Site Infection.

2. Clinical Question

3. Trial Design

The registry describes a prospective randomized trial in patients having bilateral breast reconstruction after mastectomy. Each participant was to receive both irrigation approaches: chlorhexidine on one breast and triple antibiotic solution on the other. This within-participant arrangement can control for characteristics shared by the two breasts, but it also means that observations from the same participant are linked. An analysis of the comparison would need to account for that pairing.

The record lists randomized allocation and double masking. It does not say which people were masked, how masking was maintained, how the breast receiving each treatment was assigned, or whether treatment assignment was balanced by side. Those details are not reported in the registry record. The registry also labels the model as single group, although its description specifies two treatments administered within each participant. This makes the design classification less informative than the description of the treatment assignment.

Enrollment was 88. The record lists the study as completed, with a start date of 2015-12 and primary completion in 2020-12. It does not provide a protocol, a sample-size justification, or a detailed account of recruitment and follow-up. The primary outcome was surgical site infection, assessed over 6 months. Although the record lists a secondary outcome concerning flap necrosis, hematoma, and seroma, it does not give results for that outcome in the information available for this analysis.

The study's paired structure is important when interpreting any counts or estimates. A comparison of totals alone would not show whether infections occurred on the same or opposite sides within a participant. The registry record does not provide the paired outcome data needed to describe that pattern.

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

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 Number of Participants With Surgical Site Infection, measured over 6 months.

The primary endpoint is the number of participants with a surgical site infection (SSI) during the stated timeframe of 6 months. At postoperative visits with the reconstructive surgeon, patients were examined for signs of infection. The registry definition includes an instance in which antibiotics were restarted, or erythema, cellulitis, warmth, purulent drainage, or fever occurred. It also describes SSI as involving cellulitis or purulent drainage.

The record classifies SSI as minor when oral antibiotics were required, major when inpatient intravenous antibiotics or operative washout were required, and explantation. These categories describe different levels of intervention or clinical consequence, but the registry record does not report counts in any category. It also does not explain how multiple qualifying signs or episodes within one participant were handled in the primary count.

A participant-level infection endpoint is clinically interpretable as a count of participants meeting the stated definition. In this bilateral design, however, treatment is assigned to separate breasts within the same participant. To compare irrigation approaches, the relevant outcome information would need to distinguish infections by breast and retain the within-participant pairing. The registry record does not report those details or the primary endpoint results. The listed definition therefore clarifies what was to be counted, but it does not establish how often SSI occurred under either irrigation approach.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

The endpoint is binary at the participant level: a participant either meets the SSI definition during the 6-month timeframe or does not. The registry describes an event definition and clinical categories, but does not report the observed primary counts or the statistical method used to compare treatments. The explanations below are general statistical context, not a description of analyses confirmed in the registry record.

Why pairing matters

When each participant receives both treatments, the two outcomes from that participant are paired. General methods for paired binary outcomes use information about whether the outcome occurred under neither approach, under both approaches, or under only one approach. The last pattern is especially informative for a within-participant contrast. Simply treating all observations as independent would ignore the relationship between breasts belonging to the same participant. The registry record does not report the paired outcome pattern or identify a method used to account for it.

For this design, treatment assignment is associated with a breast within each participant, while patient characteristics are shared across the pair. Pairing can make a comparison more focused on differences between the two breasts, but it does not remove every possible source of bias or measurement variation. It also does not eliminate the need to report how assignment was performed, how outcomes were assessed, and how missing observations were handled. Those implementation details are not reported in the registry record.

What an effect estimate and confidence interval would convey

In general, an effect estimate summarizes the contrast between treatments on a specified scale, while a confidence interval describes the uncertainty around that estimate under the analysis assumptions. A narrow interval indicates greater statistical precision than a wide interval; either interval can still include values consistent with different interpretations. A p-value, when reported, addresses compatibility between data and a specified null hypothesis under a statistical model. It does not measure the probability that a treatment works, nor does it describe the size or practical importance of an effect.

No effect estimate, confidence interval, or p-value for the primary endpoint is reported in the registry information available for this analysis. It is therefore not possible to assess precision or statistical evidence for the primary comparison. General explanations of these quantities should not be mistaken for a description of an analysis that the registry record documents.

Binary counts and sparse outcomes

For a binary endpoint, event counts and the number of participants at risk are basic ingredients for describing frequency. With paired data, those totals alone may not be enough to reconstruct a valid treatment contrast, because the joint outcomes within participant pairs matter. If events are uncommon, some paired outcome patterns may contain few observations. General statistical methods can behave differently when data are sparse, and the choice of method can affect uncertainty estimates. The registry record does not report whether SSI was sparse or which method, if any, was selected.

Over-dispersion is a general concern when observed variability exceeds what a chosen model assumes. For a simple binary outcome, model assumptions should reflect both the outcome type and the dependence induced by pairing. The registry record does not identify a model or report diagnostics, so no model fit or over-dispersion assessment can be described for this trial.

Planning illustrations are not observed power

The record describes a planning illustration using a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation, with the target effect expressed as a stated fraction of the observed effect. A planning illustration estimates the sample size that would be needed under specified assumptions; it is not the trial's observed power and does not show that a result is statistically significant. In a paired design, assumptions about the relationship between paired outcomes are also relevant to planning. The registry record does not report the trial's own sample-size justification or the paired assumptions used for planning.

The observed primary effect and resulting sample-size values are not reported in the registry information available for this analysis. Thus, the stated planning framework can be described, but its numerical implications cannot be interpreted from the registry record. Any planning calculation should be kept distinct from outcomes actually observed and from a sponsor's analysis, if one is reported elsewhere.

Analysis choices that remain undocumented

The registry lists no analyses. It does not report whether the comparison used an intention-to-treat population, a per-protocol population, or another analysis set; how missing outcome observations were treated; whether the primary comparison was adjusted; or whether an interim analysis was planned or performed. It also does not specify a statistical test or model. These omissions prevent verification of the intended inferential procedure and its assumptions. The posted description establishes the endpoint and treatment arrangement, but not the analysis plan or primary statistical result.

10. Multiplicity, Missing Data and Analysis Populations

Multiplicity arises when multiple outcomes, comparisons, timepoints, or analyses are examined. In general, the more statistical tests undertaken, the greater the chance of obtaining a nominally unusual result by chance if no adjustment or prespecified hierarchy is used. The registry lists SSI as the primary endpoint and lists a secondary outcome concerning participants with flap necrosis, hematoma, and seroma. It does not report a multiplicity strategy, a hierarchy among outcomes, or the statistical analyses performed. The number of analyses listed in the registry is zero.

The stated primary timeframe is 6 months. The record describes assessment at postoperative visits but does not provide visit schedules, outcome completeness, or missing-data counts. It does not state how participants with incomplete follow-up were handled, whether missing observations were imputed, or how any sensitivity analyses were conducted. Missingness could matter if infection status was not established for every participant and breast, but the registry does not provide enough information to determine whether that occurred.

The analysis population is also not reported in the registry record. There is no description of exclusions after randomization, adherence to assigned irrigation, or whether all enrolled participants contributed to the primary endpoint analysis. In a paired design, incomplete data for either breast may affect the usable within-participant comparison. Without an analysis population and missing-data account, the amount and direction of any resulting uncertainty cannot be assessed.

These are reporting gaps, not evidence that particular procedures were or were not used. The registry does not document an interim analysis, statistical plan, multiplicity adjustment, or missing-data method. No conclusion about those practices should be inferred from their absence in the record.

11. Safety Results

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

Deaths

Other (non-serious) adverse events

Participants with at least one non-serious event at or above the registry's 0% reporting threshold.

Most frequent non-serious adverse event terms

The registry lists serious adverse events for each irrigation group among 88 participants at risk: 0 in the chlorhexidine group and 0 in the triple antibiotic group. It lists no serious adverse-event terms. These entries describe what is recorded in the safety fields; they do not establish that no serious events of any kind occurred outside the registry's reporting definitions or period. The record does not give further detail about safety surveillance or event attribution.

For other adverse events, the registry lists 33 in the chlorhexidine group and 29 in the triple antibiotic group, with 88 participants at risk in each group. It also lists 2 deaths in each group. The record does not explain whether these figures represent participants, event counts, or another reporting unit beyond the labels and fields, nor does it give event descriptions, timing, severity, or causal relationship to irrigation. The figures should therefore be read as registry safety entries, not as a comparative safety analysis.

Because each participant received both irrigation approaches, the two group entries are not necessarily independent participant groups. The registry does not explain how safety events were assigned in this within-participant design. These safety figures are distinct from the primary SSI outcome and cannot be used to reconstruct its result.

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

The record establishes that investigators planned a randomized comparison of two irrigation approaches in bilateral breast reconstruction and specified SSI as the primary endpoint over 6 months. It also gives a clinical definition that includes antibiotic restart and specified signs of infection, with severity categories based on treatment or explantation. These details make the intended outcome understandable.

What the record does not establish is how many participants experienced SSI under either approach, how infections were distributed between paired breasts, or what the estimated treatment contrast was. There is no reported confidence interval or p-value for the primary endpoint. Therefore, the registry information does not show whether the outcome differed between approaches, how large any difference might have been, or how precisely it was estimated.

The trial's completed status and its enrollment of 88 do not supply those missing results. Likewise, the safety entries cannot be substituted for primary endpoint results. A zero count in the serious adverse-event fields is not the same as a zero SSI count, and the other adverse-event and death entries are not accompanied by enough detail for a comparative safety interpretation.

More broadly, absence of a posted analysis should not be interpreted as evidence of no effect, no risk, or equivalence. Equivalence or non-inferiority would require an appropriate design, prespecified margins, and a reported analysis; these are not reported in the registry record. The appropriate statistical conclusion is limited: the treatment question and intended design are described, but the primary comparative result is not available in the registry information. A reader should distinguish that reporting limitation from an outcome observed in the trial.

13. Why This Trial Matters Statistically

This trial is statistically notable for its within-participant structure. Each participant was intended to receive both irrigation approaches, one on each breast. That arrangement can make a direct paired comparison possible, but it also requires outcome reporting that preserves the link between the two breasts. Counts organized only by treatment group would not necessarily reveal the paired pattern needed to understand the comparison.

The registry combines a randomized, double-masked description with a single-group model label. The treatment description clarifies that both approaches were used within participants, but the registry classification does not explain how this structure was represented in the planned analysis. The record also does not state which people were masked or how assignment to breast was carried out. These details matter because they help readers assess the design and the assumptions behind a statistical comparison.

The endpoint definition is clinically specific, but the primary result is absent. That difference illustrates why a clear outcome definition and a reported analysis are both necessary for statistical interpretation. An endpoint definition tells readers what investigators intended to count; it cannot by itself show the frequency of events, the treatment contrast, or its precision.

Finally, registry safety entries and planning assumptions answer different questions from the primary outcome analysis. Safety fields describe reported events, while planning calculations concern assumptions about the sample size needed for a target effect. Neither replaces observed paired SSI results. The record's gaps make transparent reporting of participant flow, side-specific outcomes, paired analysis, and uncertainty especially important for understanding this design.

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.

The main trial-specific limitation of the registry information is the absence of primary SSI results. It does not provide event counts by breast or treatment, the paired outcome pattern, an estimated contrast, or a measure of uncertainty. Without these, the intended comparison cannot be quantitatively interpreted.

The design description and registry classification are not fully aligned: the model is labeled single group, while the description states that each participant receives both treatments. The record does not clarify the allocation procedure for assigning treatment to each breast, whether breast side was balanced, or how the paired structure was handled in analysis. It also does not identify who was masked, despite listing double masking.

Details that would support assessment of outcome validity are not reported, including participant characteristics, eligibility criteria, completeness of follow-up, the number of infections in each severity category, and how repeated signs or episodes were counted. The record does not report the primary analysis population, missing-data handling, adjustment strategy, or statistical method. The listed secondary outcome has no result in the information available for this analysis.

Safety reporting is also limited. The registry lists serious-event, other-event, and death figures but gives no event descriptions, timing, attribution, or explanation of their reporting unit. The trial's own sample-size justification is not reported, and the planning assumptions do not provide the missing primary result. These limitations concern what can be interpreted from the registry record; they do not establish that the underlying study lacked additional procedures or analyses.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Surgical Site Infection With 0.05% Chlorhexidine (CHG) Compared to Triple Antibiotic Irrigation — NCT02395614.
• Registry record last updated 2022-01-26; status last verified 2022-01.
• Results first posted 2022-01-26.
• 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.

18. Record Summary

The registry describes a completed randomized trial of irrigation during immediate tissue expander breast reconstruction after mastectomy. Each participant was to receive chlorhexidine on one breast and triple antibiotic solution on the other. Enrollment was 88, and the primary endpoint was the number of participants with SSI over 6 months.

The record defines SSI and lists minor, major, and explantation categories. It also lists a secondary outcome concerning flap necrosis, hematoma, and seroma. Primary SSI counts, the paired treatment comparison, an effect estimate, and inferential results are not reported in the registry information available for this analysis. The registry lists no analyses and does not describe the analysis population or missing-data handling.

Safety entries list 0 serious adverse events in each irrigation group, other adverse-event counts of 33 and 29, and 2 deaths in each group. These entries lack detail for a comparative interpretation. The record supports describing the trial's question and design, but not concluding how the primary outcome differed between irrigation approaches.