The Impact on Linkage-to-care of an Alternative Hepatitis C Screening Method in PWID: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for The Impact on Linkage-to-care of an Alternative Hepatitis C Screening Method in PWID (NCT02971488), a registered phase not stated study. The primary outcome is Percentage of Participants Who Achieved a Sustained Virological Response (SVR).

2. Clinical Question

The clinical question concerns a linked service pathway rather than screening in isolation. The registry describes screening in Cañada Real Galiana, contact with people whose screening result was positive, an offer of referral to Hospital Universitario Infanta Leonor for standard confirmation tests, and access to hepatitis C treatment. It also describes follow-up to assess health-related aspects of the program, including appointments in health centers, treatment, and virological response.

The record frames screening and treatment within a harm-reduction context. Its background describes the importance of more frequent diagnosis, avoiding loss of tracking, and access to antiviral treatment as related strategies. These are the rationale recorded for the program, not findings that establish the impact of this particular study.

The primary outcome is a participant count labelled as the percentage achieving sustained virological response. The registry does not provide the observed count or percentage, nor a comparison estimate. Therefore the clinical question can be described from the planned pathway and endpoint, but its numerical answer cannot be read from the registry record.

3. Trial Design

The registry describes a completed study titled “The Impact on Linkage-to-care of an Alternative Hepatitis C Screening Method in PWID.” The listed intervention is “Screening for HCV in PWID and Linkage-To-Care,” classified as an other intervention. Enrollment is recorded as 529 participants. The study population is described as people who inject drugs who visit Cañada Real Galiana on the outskirts of Madrid.

The program description links screening to follow-up and care. People with positive screening results were to be contacted and offered referral to Hospital Universitario Infanta Leonor for standard confirmation tests. The description says that treatment would be accessible and that follow-up would assess aspects such as health-center appointments, treatment, and virological response. The primary outcome is sustained virological response, with a stated timeframe of two years.

The record marks the study completed and lists a start date of 2017-01-15 and a primary completion date of 2018-12-31. These dates describe the registry record; they do not, by themselves, establish when every participant was enrolled or followed.

This is not presented as a randomized comparison. The allocation method is not stated, and the record does not describe arms as a like-for-like control comparison. Consequently, the design information does not support interpreting an outcome difference between intervention and control groups. In addition, the posted record does not give a detailed protocol, eligibility criteria, recruitment flow, or analysis plan. Those design details are not reported in the registry record.

The registry lists secondary outcome topics concerning active hepatitis C among the screened population and the prevalence of other chronic viral infections. It records six outcome measures overall, but the available record does not provide numerical findings for those measures. The design can therefore be described as a screening and linkage-to-care program with follow-up outcomes, while its observed clinical results remain unavailable 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

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 Percentage of Participants Who Achieved a Sustained Virological Response (SVR), measured over 2 years.

The primary outcome is titled “Percentage of Participants Who Achieved a Sustained Virological Response (SVR).” Its unit is participants, its recorded parameter is a count of participants, and its timeframe is two years. The outcome is intended to describe a treatment-related result among participants in the screening and linkage-to-care pathway. The program description says that people with positive screening results could be contacted, referred for confirmation testing, and given access to hepatitis C treatment, with follow-up that included assessment of virological response.

In general, a primary endpoint is the principal outcome used to address a study’s main question. A virological response is relevant to this program because the pathway extends beyond detecting infection: it also aims to connect people with confirmatory testing and treatment. A participant count can indicate how many people meet the endpoint definition, while a percentage requires a defined denominator. The record gives the endpoint title and unit but does not report the observed count, percentage, denominator used for the percentage, or a detailed operational definition of sustained response.

The two-year timeframe is recorded, but the specific timing of endpoint assessment within that period is not described. The registry record also does not provide a numerical primary outcome result or an estimate of precision. Thus, the endpoint identifies what the program intended to assess, but the record does not allow readers to quantify the observed response or assess how precisely it was estimated.

7. Why No Re-analysis Is Shown

8. Statistical Interpretation

9. Statistical Methods Explained

Statistical methods help translate observed participant outcomes into estimates that can be interpreted in light of uncertainty and study design. In this record, the outcome is described as a count of participants who achieve sustained virological response, and the study is identified as a screening and linkage-to-care program. The numerical results needed to apply many statistical methods are not reported in the registry record.

What does a participant count represent?

A count records the number of participants meeting an outcome definition. To express that count as a percentage, an analysis also needs a denominator: the group of participants to whom the percentage applies. In general, the denominator should match the question being asked. For example, a proportion among all enrolled participants answers a different question from a proportion among those who were screened, referred, treated, or assessed at follow-up. The record identifies the outcome unit as participants but does not specify the denominator used for a reported percentage or provide a result.

For a binary outcome, each participant is classified according to whether the defined event occurred. In general, the observed proportion is the event count divided by the relevant denominator. No new estimate can be recovered because the event count and endpoint-specific denominator are not reported. The registry’s enrollment figure alone cannot substitute for an endpoint denominator, since the record does not describe participant flow or the number with outcome assessment.

What would uncertainty estimates add?

In general, a confidence interval communicates uncertainty around an estimate. A narrower interval indicates greater precision under the assumptions of the method; a wider interval indicates more uncertainty. The interval does not repair bias or make a non-comparative design causal. For this study, the registry record does not report a confidence interval for sustained virological response or a numerical estimate around which one could interpret precision.

When a study compares groups, the analysis must also account for how participants entered those groups and whether the groups are comparable. Here, the allocation method is not stated, and the record does not describe a suitable control comparison. An estimate from a non-randomized comparison can be affected by differences between groups, selection into care, or other factors. These are general concerns about interpretation; the registry record does not provide enough information to establish whether any particular bias occurred.

How should planning illustrations be understood?

In general, sample-size calculations are planning tools. The stated planning assumptions describe a two-sided significance level of 0.05, equal allocation between two arms, and a normal approximation. They also describe planning for stated fractions of an observed effect. Such calculations are illustrations of the sample size that might be needed under those assumptions, not evidence about what the study observed. They are not observed power.

The planning description says that non-time-to-event illustrations are expressed as participants per arm, while time-to-event illustrations are expressed as total events. Those conventions matter because sample-size quantities have different meanings depending on the outcome model. The registry record does not report the study’s own design justification, and the assumptions in a planning illustration should not be mistaken for the original protocol’s rationale. The numerical planning outputs are not stated in the registry record.

In general, a planning calculation based on an observed effect is illustrative rather than prospective design evidence: its value depends on the effect used as the starting point and on the assumptions about allocation and analysis. It does not establish that the study had adequate power, and it cannot replace an observed effect estimate with uncertainty. No sample-size illustration should be interpreted as observed power or as a result of the study.

What analysis details are unavailable?

The record lists six outcome measures and records zero analyses. It does not report the statistical model, any adjustment variables, the method for handling repeated or incomplete measurements, or whether results were analyzed according to a prespecified plan. The primary outcome is a participant count, but the analysis population and endpoint-specific denominator are not described. These missing details prevent a fuller assessment of how the outcome would be summarized and how uncertainty would be quantified.

In general, an analysis plan specifies how outcomes, missing observations, and multiple endpoints will be handled before results are interpreted. Those choices can affect estimates and their uncertainty. The record does not describe an analysis plan or interim analyses. It also does not report a detailed endpoint definition, making it impossible to assess from the registry record whether the measured outcome followed a particular threshold or assessment schedule.

The central methodological distinction is between the stated program and the evidence needed to estimate its outcome. The registry describes a pathway and an endpoint, but does not post the outcome counts or analysis needed to quantify a result. Statistical interpretation must remain limited to that information.

10. Exact Estimates for Each Arm

No two-arm comparison is shown for this trial, but each arm's result can still be summarized with exact interval estimates computed from the posted counts. The Clopper-Pearson interval is exact and conservative; the Wilson interval is a common closer-to-nominal alternative; the Bayesian credible interval uses a uniform Beta(1, 1) prior. For small groups the three can differ noticeably.

R code and output

arm    <- c("HCV Infected Patients", "Patients Who Started HCV Therapy")
n      <- c(122, 52)
events <- c(38, 38)
for (i in seq_along(n)) {
  ci <- binom.test(events[i], n[i])$conf.int          # Clopper-Pearson exact interval
  cr <- qbeta(c(0.025, 0.975), 1 + events[i], 1 + n[i] - events[i])   # Bayesian, uniform Beta(1,1) prior
  wi <- (function(x, n) { p <- x / n; z <- qnorm(0.975); d <- 1 + z^2 / n
    c((p + z^2 / (2 * n) - z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d, (p + z^2 / (2 * n) + z * sqrt(p * (1 - p) / n + z^2 / (4 * n^2))) / d) })(events[i], n[i])
  cat(sprintf("ARM|%s|%d|%d|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f|%.1f\n", arm[i], n[i], events[i], 100 * events[i] / n[i],
              100 * ci[1], 100 * ci[2], 100 * wi[1], 100 * wi[2], 100 * cr[1], 100 * cr[2]))
}

ARM  HCV Infected Patients  122  38  31.1  23.1  40.2  23.6  39.8  23.6  39.9
ARM  Patients Who Started HCV Therapy  52  38  73.1  59.0  84.4  59.7  83.2  59.7  83.2

11. Multiplicity, Missing Data and Analysis Populations

The registry lists six outcome measures. It identifies sustained virological response as the primary outcome and names secondary topics concerning active hepatitis C in the screened population and prevalence of other chronic viral infections. The record does not provide a complete outcome-by-outcome results account, nor does it report a plan for controlling the risk of false-positive findings when examining multiple outcomes. A multiplicity strategy is not reported in the registry record.

In general, multiplicity refers to the increased chance of finding at least one apparently notable result when many outcomes or analyses are examined. A prespecified primary outcome can help focus interpretation, but it does not reveal whether other analyses were planned, adjusted, or selectively reported. The registry record does not describe such procedures, and it records zero analyses.

The record also does not describe missing-data methods or an analysis population. It gives an enrollment figure but no flow showing how many participants were screened, referred, treated, or assessed for the primary outcome. It does not report the endpoint denominator, the amount of missing outcome information, or how any missing observations were handled. These details are not reported in the registry record.

In general, missing outcomes can affect both the denominator and the interpretation of a proportion, especially if participants without assessment differ from those with assessment. Without information on follow-up completeness and analysis populations, the effect of missingness cannot be evaluated. Interim analyses and any statistical analysis plan are also not reported in the registry record. These absences mean that neither multiplicity nor missing-data handling can be incorporated into an assessment of the posted results.

12. 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 adverse-event record lists 529 participants at risk for serious adverse events and 529 at risk for other adverse events. It records zero affected participants in each category and zero deaths. No top serious adverse-event terms are listed. These are the figures entered in the registry record; they should be read as recorded counts, not as proof that no event occurred in any broader sense.

In general, an at-risk count indicates the number of participants represented in a safety category, while an affected count indicates how many were recorded as having the relevant event. Interpretation depends on the event definitions, collection procedures, observation period, and completeness of reporting. The registry record does not provide those details, including a safety-specific timeframe or definitions for the event categories.

The safety figures also do not describe the timing, severity breakdown, relationship to the intervention, or exposure to treatment. The study’s intervention is a screening and linkage-to-care program, but the record does not explain how adverse events were attributed or monitored. Accordingly, the zero counts should be presented as the posted registry figures only. They do not establish that the program had no risks, and they do not support comparisons with another group because no suitable control comparison is described.

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

The registry record documents a completed study of hepatitis C screening and linkage-to-care among people who inject drugs visiting Cañada Real Galiana. It records enrollment of 529 participants, identifies the program pathway, and names sustained virological response as the primary outcome over a two-year timeframe. These registry entries establish what the study set out to assess, not what it found.

The record does not report the primary outcome count or percentage. As a result, it does not show how often sustained virological response was achieved or how precisely that result was estimated. It also does not provide numerical results for the listed secondary outcome topics. The absence of posted results should not be interpreted as a positive or negative clinical finding.

The design information further limits interpretation. Allocation is not stated, and no like-for-like control comparison is described. Consequently, the registry information cannot support a comparative estimate of the effect of the screening method or linkage-to-care pathway. Even if an outcome count were available, a descriptive result among participants would not by itself separate program effects from other influences.

In general, evidence about a program includes both the observed outcome and the design and analysis choices that produced it. Here, the record lacks endpoint-specific denominators, participant flow, missing-data methods, a detailed statistical plan, and measures of uncertainty. These omissions make it impossible to assess the magnitude, precision, or robustness of an outcome estimate from the registry record.

The defensible conclusion is narrow: a completed program is registered, and its rationale, population, intervention, and primary outcome are described. The numerical clinical result is not reported in the registry record. No claim that the intervention succeeded, failed, or changed outcomes is supported by the information available there.

14. Why This Trial Matters Statistically

This study addresses a statistical question that is broader than whether screening detects hepatitis C. Its registered pathway connects screening with contact, confirmation testing, referral, treatment access, and follow-up. The primary outcome, sustained virological response, is positioned at the end of that pathway. That makes the distinction between screening activity and downstream outcome measurement important: participants may move through several stages before the primary endpoint can be assessed.

For statistical interpretation, each stage requires clear denominators and follow-up information. In general, the number screened, the number with positive results, the number reached, and the number with an assessed treatment outcome answer different questions. The registry record does not give those stage-specific counts. Enrollment alone cannot show where participants may have been lost along the pathway or what proportion reached outcome assessment.

The study also illustrates why design matters when interpreting a program’s observed results. Without a stated allocation method or a suitable control comparison, a reported outcome would primarily describe what happened among participants in the program. It would not by itself establish what would have happened under an alternative screening or care pathway. This is a general limitation of non-comparative evidence, not a finding that any particular bias occurred in this study.

The record is statistically informative about the intended population, intervention, endpoint, and timeframe, but it does not post the primary result or a precision estimate. That contrast matters: a registry entry can document a research question while leaving its numerical answer unavailable. Readers should distinguish a registered endpoint from a reported finding and should not treat study completion or enrollment as evidence of effectiveness.

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.

The registry record leaves several limitations specific to interpreting this study. It describes the population as people who visit Cañada Real Galiana, but does not give detailed eligibility criteria, recruitment procedures, or a participant flow. The extent to which the enrolled participants represent other people who inject drugs, including those outside this setting, cannot be assessed from the record.

The intervention description outlines screening, contact after a positive result, referral for confirmation testing, treatment access, and follow-up. However, it does not report how many participants proceeded through each stage. Without those counts, the reach of the pathway and the endpoint denominator are unknown. The primary outcome title refers to a percentage, while its unit is participants and its parameter is a count; the record does not explain how the percentage denominator was defined.

The outcome definition is also incomplete. The record names sustained virological response and gives a two-year timeframe, but does not provide a detailed assessment schedule or operational criteria. No numerical primary or secondary outcome results, confidence intervals, or analysis details are reported. The registry record also does not describe missing-data handling, analysis populations, multiplicity procedures, or interim analyses.

Finally, allocation is not stated and a like-for-like control comparison is not described. Any causal interpretation of a program effect would therefore be unsupported by the design information in the record. The adverse-event fields record zero affected participants, but do not provide detailed definitions, observation periods, or collection procedures. These limitations restrict both effectiveness and safety interpretation; they do not establish that the program had no effect or that no adverse events occurred.

16. Related Tutorials

17. Related Statistical Calculators

18. Sources

• ClinicalTrials.gov: The Impact on Linkage-to-care of an Alternative Hepatitis C Screening Method in PWID — NCT02971488.
• Registry record last updated 2019-09-13; status last verified 2019-08.
• Results first posted 2019-09-13.
• 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 record describes a completed screening and linkage-to-care study involving people who inject drugs visiting Cañada Real Galiana on the outskirts of Madrid. It records enrollment of 529 participants and identifies sustained virological response over two years as the primary outcome. The pathway included screening, contact after a positive result, an offer of referral for confirmation testing, and access to treatment.

The allocation method is not stated, and the record does not describe a like-for-like control comparison. It lists six outcome measures, including secondary topics on active hepatitis C and other chronic viral infections, but reports no numerical outcome analyses. The primary result, endpoint denominator, and statistical analysis details are not reported in the registry record. Safety fields list zero affected participants and zero deaths among 529 at risk in each recorded category; event definitions and observation details are not given. The entry describes the study question and design, but does not provide enough results to quantify the program’s outcomes or their precision.