Rapid Flu Tests in Travelers With Fever: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Rapid Flu Tests in Travelers With Fever (NCT00821626), a randomized na study. The primary outcome is Cost for the Medical Management of Patients.

2. Clinical Question

The clinical question concerns the role of a test in management, rather than only whether the test identifies influenza. A test could affect clinical decisions and resource use; the primary outcome selected for this trial was the cost of medical management. Chest X-ray requests and antibiotic prescriptions were also listed as secondary outcomes, giving additional indicators of care use. Those outcomes do not, by themselves, establish whether management was appropriate or whether a particular decision was caused by the test. The registry describes a randomized comparison, but the posted primary results are arm-specific means and confidence intervals rather than a reported estimate of the between-arm contrast. The clinical question can therefore be described, while the registry's posted primary results do not supply a formal answer to the comparison in that question.

3. Trial Design

The registry describes NCT00821626, titled “Rapid Flu Tests in Travelers With Fever,” as a randomized, parallel-arm trial with no masking. Its official title is “Utility of Rapid Flu Tests in the Medical Management of Returning Travelers With Fever.” The study is marked completed. The registry lists an enrollment of 93, with 60 participants in the Rapid Test arm and 33 in the Comparator arm.

The intervention was BD Directigen EZ Flu A+B, classified as a device. The comparator was usual medical care without a rapid flu test. The brief summary presents the study population as returning travelers with fever and an intermediate risk of influenza infection. The record gives a study start of 2009-01 and a primary completion of 2015-05. The phase is listed as NA, and the sponsor is University of Lausanne Hospitals.

Randomization is a design feature intended, in general, to make assigned groups comparable on average at the time of allocation. It does not ensure that every characteristic is balanced in a particular trial, and the registry record does not report the randomization procedure, allocation concealment, or baseline characteristics in the information available for this analysis. Because masking is listed as none, participants and clinical staff were not described as masked to assignment. Whether outcome assessment or cost accounting was masked is not reported in the registry record.

The record reports arm-level primary outcome summaries and secondary outcome counts. It does not report a primary-outcome hypothesis test or a named analysis population. The primary outcome timeframe is 4 years; what that timeframe represents operationally, including the precise measurement schedule and cost components, is not reported in the registry record. No assumptions about those design details should be inferred from the summary results.

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 Cost for the Medical Management of Patients, measured over 4 years.

The primary endpoint is titled “Cost for the Medical Management of Patients.” It is a continuous outcome measured in USD, with the registry reporting a mean and a 95% confidence interval for each arm. The timeframe is 4 years. The reported mean is the average cost within an arm as represented in the registry; it is not itself an estimate of the difference between randomized groups.

Cost is used in this trial because the stated objective concerns whether rapid flu testing influences medical management. In general, a cost endpoint can capture resource use associated with care, including the financial consequences of diagnostic and treatment decisions. It can therefore address a different question from whether the test detects influenza accurately. The registry record does not specify which cost categories were included, how costs were measured or valued, whether the outcome covers the full 4-year period for every participant, or how incomplete cost information was handled. Those details are important to understanding what the mean represents and are not reported in the registry record.

The arm-specific means are 581 USD for Rapid Test, with a 95% confidence interval from 454 to 707, and 661 USD for Comparator, with a 95% confidence interval from 522 to 800. The registry does not report a primary-outcome contrast or its confidence interval. The means therefore describe the posted arm summaries, but do not establish the size or precision of a between-arm cost effect.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

What does a mean describe?

In general, the mean is the arithmetic average of observed values in a group. For a cost endpoint, a mean summarizes the group's average recorded cost, but does not show the spread, skewness, or individual cost patterns. Cost data can be unevenly distributed: a small number of high values may have a strong influence on an average. The registry reports means and confidence intervals but no standard deviations, medians, cost distribution, or analysis method. It is therefore not possible to assess from the record how the cost data were distributed or how the intervals were calculated.

The primary outcome reports 581 USD for Rapid Test and 661 USD for Comparator, each with its own 95% confidence interval. These arm-specific summaries should not be confused with the randomized comparison. To quantify the contrast, an analysis would ordinarily report a difference or another prespecified comparison measure with uncertainty. Such a primary comparison is not reported in the registry record. No recalculated primary comparison is presented.

How should confidence intervals be read?

In general, a confidence interval expresses the sampling uncertainty around an estimate under the assumptions of the method used. A narrower interval indicates greater precision for that estimate than a wider interval, all else equal. It does not mean that every individual observation lies inside the interval, and it does not assign a probability to a fixed effect after the data have been observed. The 95% label describes the coverage property of the method across repeated applications under its assumptions.

For an arm-specific mean, the interval concerns that mean. For a difference between arms, the relevant interval would concern the difference. Separate arm intervals do not directly provide the same information as a confidence interval for the contrast. Since the record gives no primary contrast interval, the uncertainty around the primary comparison is not reported. In contrast, the secondary-outcome summaries include risk-difference estimates and confidence intervals, so those comparisons can be read directly as reported, while retaining their unadjusted status.

What do the secondary risk differences mean?

In general, a risk difference is the difference between the proportions of participants with an outcome in two arms, expressed on the proportion scale. The registry labels the Rapid Test arm as the comparison and reports the risk differences, confidence intervals, and unadjusted p-values for the secondary outcomes. Positive and negative signs indicate opposite directions under the stated arm ordering. A confidence interval spanning zero is compatible with no difference under the interval method, as well as with effects in either direction covered by the interval. It is not proof that the arms are identical.

The listed p-values are unadjusted. In general, a p-value measures how unusual data at least as incompatible with a specified null hypothesis would be under that hypothesis and the analysis assumptions. It is not the probability that the null hypothesis is true, nor does it measure the clinical importance of an outcome. These p-values do not account for the fact that more than one secondary outcome was reported. They should therefore be interpreted cautiously and alongside the estimates and their intervals, rather than as standalone declarations.

What are the planning illustrations?

The record includes planning illustrations based on fractions of the observed secondary effects. The stated assumptions are a two-sided significance level of 0.05, equal allocation between arms, and a normal approximation. The figures are participants per arm for the stated power targets. They are illustrations of sample sizes under those assumptions, not the trial's original design calculation and not observed power. The registry does not report the trial's own sample-size justification, assumptions used when planning enrollment, or whether an original target was met.

In general, a planning calculation estimates the sample size that would be required to detect an assumed effect under a specified model and design. Its result depends on the effect size chosen, the variability or event rates assumed, the significance threshold, allocation, and other assumptions. When the assumed effect is based on an observed estimate, it is especially important not to treat the illustration as independent confirmation of that effect. The stated fractions represent hypothetical planning scenarios, not new trial results. The record gives no corresponding planning illustration for the primary cost outcome.

The registry reports no analyses for the primary outcome and no reported analyses for the secondary outcomes. The secondary comparisons included in the posted summaries are unadjusted recalculations, not sponsor-reported analyses. No adjustment for covariates, center, baseline differences, or other factors is described. The analysis methods used by the trial team, including any model for cost, any prespecified handling of skewness, and the exact methods for confidence intervals, are not reported in the registry record. The posted summary statistics can be interpreted as descriptive results, but they do not reveal the full analysis plan or the data-level methods behind the trial's results.

In general, over-dispersion means that the observed variation is greater than a statistical model assumes. It matters because model-based uncertainty estimates can be too small if the model understates variability. For binary outcomes, differences in underlying event probabilities and small counts can also affect the reliability of approximations. The registry's planning assumptions explicitly include a normal approximation, but does not report a diagnostic assessment of that assumption. No conclusion about whether a particular approximation was suitable for the trial's data should be inferred from the planning illustration alone.

10. Multiplicity, Missing Data and Analysis Populations

The registry lists one primary outcome and two secondary outcomes, but does not report a multiplicity plan. It does not state whether the secondary outcomes were intended to be confirmatory, whether testing was to follow a hierarchy, or whether any adjustment was planned for multiple comparisons. The reported secondary p-values are unadjusted. In general, when several outcomes are examined, the chance of at least one apparently unusual result can increase if each is judged independently using the same threshold. This is why secondary p-values without a stated multiplicity strategy are usually interpreted as exploratory rather than definitive.

The record reports no analyses for the primary outcome and no reported analyses for the secondary outcomes. It does not describe interim analyses, stopping rules, or a statistical analysis plan. Those details are not reported in the registry record; their absence from the record does not establish that they did or did not exist outside it. No assumptions about when outcomes were selected or how analyses were conducted can be made from the posted summaries.

Missing-data handling and analysis populations are also not reported in the registry record. The record does not say whether the primary endpoint was available for every randomized participant, how incomplete cost records were handled, or how participants were assigned to the analysis populations. It does not identify an intention-to-treat, per-protocol, or other named population. Group counts are available for the outcome summaries, but those counts alone do not explain whether any observations were missing or excluded.

In general, missing outcomes can affect both the estimate and its uncertainty when the probability of missingness is related to participant characteristics or outcomes. The direction and size of such effects depend on the missingness pattern and the analytic approach. Without information about completeness, exclusions, and sensitivity analyses, the effect of missing data cannot be assessed. These reporting gaps limit confidence in any inferential interpretation, particularly because a primary comparison is not posted and the secondary results are unadjusted.

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 5% reporting threshold.

The posted safety figures report zero serious adverse events, zero other adverse events, and zero deaths in the Rapid Test arm, with 60 participants at risk for each listed measure. The Comparator arm reports zero serious adverse events, zero other adverse events, and zero deaths, with 33 participants at risk for each listed measure. No serious adverse-event terms are listed.

These are registry counts, not evidence that no adverse experiences occurred outside the recorded definitions, collection period, or reporting process. The record does not provide event definitions, severity grading, relatedness to the intervention, duration of safety follow-up, or details of ascertainment. It also does not describe whether the safety summaries include all randomized participants or a different population.

In general, a zero count in a trial does not establish that an event is impossible or that two interventions have identical safety. Rare outcomes may not be observed in a study of limited size, and the information does not support a precise comparative safety estimate. The figures should be read as the events recorded in the registry, with the reporting and follow-up details not reported in the registry record.

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

The registry establishes that a randomized, open-label comparison was conducted between rapid flu testing and usual care without a rapid test in returning travelers with fever. It posts arm-specific mean medical-management costs and secondary counts for selected care-use outcomes. Those summaries provide descriptive information about the recorded outcomes in the trial arms.

The posted primary means are 581 USD for Rapid Test and 661 USD for Comparator, with the respective 95% confidence intervals reported in the registry. The record does not provide a primary between-arm estimate, interval, or p-value. Consequently, the numerical ordering of the means is not, on its own, a complete statistical comparison. The record does not establish the size or precision of a primary cost contrast, nor does it support a claim that the rapid test did or did not change medical-management cost.

The secondary outcomes show mixed directions and are reported with unadjusted comparisons. They do not establish a coherent change in all aspects of care, and they do not explain the primary cost summaries. The absence of a multiplicity plan, analysis-population details, missing-data methods, and outcome definitions further limits the conclusions that can be drawn from the posted results.

In general, a randomized design can support causal interpretation when the allocation process is properly conducted and the analysis preserves the randomized comparison, but design labels alone do not guarantee that all requirements for interpretation are met. The available record does not report enough analysis detail to assess those requirements fully. The safest reading is therefore descriptive: the registry records the group summaries and outcome counts, while leaving the main statistical comparison and several aspects of its analysis unreported. These results do not establish whether rapid testing should be used in clinical practice.

13. Why This Trial Matters Statistically

This trial raises a useful statistical distinction between evaluating a diagnostic test and evaluating its consequences for care. The stated objective is about whether rapid testing influences medical management, and the primary endpoint is a cost measure rather than a measure of diagnostic accuracy. The registry also records selected care-use outcomes. Together, these choices illustrate that a test may be studied through downstream decisions and resource use, not only through its ability to classify disease.

The record also shows why arm-specific summaries are not equivalent to an estimated treatment contrast. A mean and confidence interval for each arm describe each group, but the comparison question requires an estimate and uncertainty for the contrast. The registry does not report that primary comparison. This gap is consequential: readers can see the posted group means but cannot determine from the registry whether the contrast was estimated, how it was analyzed, or how precise it was.

The secondary results illustrate another important issue. Several outcomes can offer context about care, but unadjusted analyses across multiple outcomes require restraint. The pattern is not uniform, and no multiplicity strategy is reported. An isolated p-value should not be elevated above the estimates, uncertainty, endpoint hierarchy, and analysis plan. Planning illustrations based on observed secondary effects also serve a different purpose from the trial's original sample-size justification and must not be mistaken for observed power.

Finally, the registry record demonstrates how incomplete statistical reporting limits interpretation even when numerical results are posted. Definitions, missing-data handling, analysis populations, cost components, and a primary comparison would all help readers assess what the estimates mean. The reported values remain useful descriptive evidence, but the missing details prevent a full statistical evaluation of the trial's central question.

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 trial-specific limitations follow from the information reported in the registry. First, the primary endpoint is presented as arm-specific means and confidence intervals, without a reported between-arm estimate or inferential test. This leaves the central cost comparison statistically incomplete in the record. The method used to calculate the intervals is not stated, and no measure of cost variability beyond those intervals is posted.

Second, the registry does not define the components of medical-management cost, how costs were collected or valued, or how the 4-year timeframe was applied. Without those details, readers cannot determine exactly which resources contribute to the outcome or whether the same measurement process was applied in both arms. No analysis addressing the distribution of costs is reported.

Third, the record gives no detailed description of randomization, allocation concealment, baseline characteristics, or masking of outcome assessment. The trial is listed as unmasked, but the record does not clarify whether cost assessment was conducted without knowledge of assignment. The usual-care comparator is also not described beyond the absence of a rapid test, limiting understanding of the care context.

Fourth, the secondary outcomes are limited to chest X-ray requests and antibiotic prescriptions in the posted results. Their definitions, timing, ascertainment, and relationship to the primary cost measure are not reported. The comparisons are unadjusted, and no multiplicity strategy is described. The record does not report missing-data methods, analysis populations, protocol deviations, or sensitivity analyses.

Finally, the planning illustrations use observed secondary effects and stated assumptions, but are not the trial's original design justification. The original sample-size assumptions and any interim-analysis plan are not reported in the registry record. These limitations do not invalidate the posted descriptive values, but they restrict how far those values can support an inferential or causal account.

15. Related Tutorials

16. Related Statistical Calculators

17. Sources

• ClinicalTrials.gov: Rapid Flu Tests in Travelers With Fever — NCT00821626.
• Registry record last updated 2020-04-02; status last verified 2020-03.
• Results first posted 2020-04-02.
• 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

NCT00821626 is a completed, randomized, parallel-arm trial with no masking, sponsored by University of Lausanne Hospitals. It studied rapid flu testing versus usual care without a rapid test in returning travelers with fever. The registry lists enrollment of 93, with 60 in the Rapid Test arm and 33 in the Comparator arm.

The primary outcome is mean cost for medical management in USD over 4 years. The record posts arm-specific means and 95% confidence intervals but no primary comparison. Secondary outcomes are chest X-ray requests and antibiotic prescriptions; their reported comparisons are unadjusted. The registry lists zero serious adverse events, other adverse events, and deaths in each arm.

Analysis populations, missing-data procedures, multiplicity methods, and the trial's own sample-size justification are not reported in the registry record. The posted results therefore support descriptive reading, while leaving the statistical comparison for the primary question unresolved.