Acyclovir to Treat Patients Co-infected With HIV and Herpes Viruses in Uganda: Complete Statistical Analysis

1. Trial at a Glance

This page covers the registry results for Acyclovir to Treat Patients Co-infected With HIV and Herpes Viruses in Uganda (NCT00405821), a randomized phase 2 study. The primary outcome is Progression to AIDS (CD4+ Less Than 250 Cells/Microliter or World Health Org Stage IV dx, Excluding Esophageal Candidiasis).

2. Clinical Question

3. Trial Design

This was a Phase 2, randomized, double-blind, placebo-controlled trial with a parallel-group design. The registry records quadruple masking, meaning that the masking designation extended beyond simply describing the study as double-blind, although the registry record does not specify which roles were masked. The study was conducted among people co-infected with HIV-1 and HSV-2 in Uganda.

The registry records enrollment of 440 participants, with 220 assigned to acyclovir 400mg tablets twice daily and 220 assigned to placebo tablets twice daily. The study summary describes participants taking the assigned study treatment for 2 years and attending monthly clinic visits. It also describes clinical care for genital ulcers or HIV complications, including antiretroviral therapy for participants whose disease progressed to the point of requiring it.

The primary outcome was progression to AIDS within the stated 2-year timeframe. The endpoint combined a CD4+ threshold with a clinical disease criterion: CD4+ below 250 cells per microliter or World Health Organization Stage IV disease, excluding esophageal candidiasis. The primary outcome is a count of participants meeting the endpoint, rather than a continuous measure.

The registry lists five secondary outcomes, including genital ulcer episodes, HIV-1 viral load, toxicity, adherence, and responses to antiretroviral therapy among participants who progressed. It records six outcome measures and three analyses. The original protocol’s sample-size assumptions, the rationale for the planned enrollment, and details of any interim analyses are not reported in the registry record.

4. Participant Flow and Accounting

The registry reports how participants moved through each stage of the study. All counts below are exactly as posted; missing counts are not inferred from other stages.

Before assignment: All subjects were randomized to study arm, and initiated study treatment at the time of enrollment.

Overall Study

Reasons for not completing this period:

Analysis population for the primary outcome, as defined in the registry: Intention to treat analysis of all subjects randomized on the trial meeting the primary endpoint

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 Progression to AIDS (CD4+ Less Than 250 Cells/Microliter or World Health Org Stage IV dx, Excluding Esophageal Candidiasis), measured over 2 years.

The primary endpoint counts participants who progressed to AIDS during the 2-year timeframe. Progression was defined as CD4+ below 250 cells per microliter or World Health Organization Stage IV disease, with esophageal candidiasis excluded from the Stage IV criterion. This is a composite endpoint: a participant could meet it through the laboratory threshold or through the specified clinical disease criterion.

Such an endpoint is used to represent clinically important progression through events that may arise in different ways. Combining criteria can capture both immunologic decline and advanced clinical disease, but the meaning of the result depends on the exact definition. The exclusion of esophageal candidiasis is part of the registry’s definition and should be retained when interpreting the outcome; it is not a count of every possible Stage IV condition without qualification.

The posted results report 95 participants with the endpoint in the acyclovir group and 110 in the placebo group, with 220 participants in each arm. These counts summarize the observed outcomes in the randomized groups. The registry also reports a time-to-event analysis, which accounts for the timing of events differently from a simple comparison of endpoint counts. The record does not provide further detail on how follow-up time, censoring, or missing outcome information was handled.

7. Results Posted in the Registry

• Acyclovir 400mg Tablet Twice Daily: 43.2% (95/220) versus 50.0% (110/220) on control; risk difference -6.8 percentage points (95% CI -16.1 to 2.5), risk ratio 0.86 (0.71–1.06); unadjusted two-proportion z-test p = 0.152.

8. Statistical Interpretation

9. Statistical Methods Explained

The primary endpoint is binary at the participant level: each participant either met the registry’s AIDS-progression definition during the timeframe or did not. The posted group values are event counts, with 220 participants in each arm. A simple comparison of those counts treats the outcome as a proportion in each randomized group. The unadjusted recalculation expresses the contrast as a risk difference, with acyclovir minus placebo as the direction of comparison. A negative estimate therefore indicates a lower observed event proportion in the acyclovir group in this particular calculation; it does not by itself establish a treatment effect.

What does the risk difference describe?

A risk difference is an absolute contrast between the observed risks in two groups. Its natural reference value for no difference is zero. The recalculated estimate is -0.068, and its confidence interval runs from -0.161 to 0.025. Since the interval extends across zero, the count-based estimate is not precise enough to rule out no difference at the stated confidence level. The unadjusted p-value is 0.152. A p-value describes how compatible the data are with a specified null model under the test’s assumptions; it is not the probability that the null hypothesis is true, nor a measure of clinical importance.

How do relative measures differ?

The registry also gives recalculated relative measures: a risk ratio of 0.864, with an interval from 0.706 to 1.056, and an odds ratio of 0.76, with an interval from 0.522 to 1.106. A ratio uses a multiplicative scale, where 1 is the reference value for no relative difference. A risk ratio compares risks directly, whereas an odds ratio compares odds. These measures can differ numerically because odds and risks are not the same quantity. Their intervals include 1, so the posted unadjusted relative estimates also remain compatible with no association at the interval level.

What does the Cox analysis estimate?

The registry reports a regression analysis using Cox methods, with a hazard ratio of 0.75 and a 95% confidence interval from 0.58 to 0.99; the reported p-value is p <0.05. A Cox model analyzes time to an event and uses information about when events occur, rather than relying only on whether each participant had an event by the end of follow-up. A hazard ratio compares event rates over time under the model. It is not a risk ratio, and the value should not be interpreted as an absolute difference in the proportion of participants experiencing the endpoint.

Time-to-event methods can account for participants having different observed follow-up times, often because an event has not occurred before observation ends or because follow-up is otherwise incomplete. This relies on assumptions and choices about the event process, censoring, and model specification. The registry record does not report those details, so the posted Cox estimate cannot be fully evaluated from the summary alone. The record also does not provide model covariates or indicate whether the reported model was adjusted beyond its stated method.

Why can the analyses differ?

The recalculated risk difference and the sponsor-reported hazard ratio address related but distinct statistical questions. The former is an unadjusted comparison of event counts; the latter is based on time-to-event regression. Differences in the quantity being estimated and the use of event timing can lead to different estimates and uncertainty. The registry record does not document enough analytical detail to attribute the observed difference to a particular factor. The estimates should therefore remain clearly labeled by measure and method rather than combined into a single conclusion.

Confidence intervals describe a range of values compatible with the data and the method at the stated confidence level. They convey uncertainty more directly than a thresholded p-value alone, but they do not guarantee that the true value lies within the realized interval. General statistical interpretation also depends on the design, outcome measurement, missingness, and assumptions. Details about missing-data handling, the full analysis population, and the prespecified statistical plan are not reported in the registry record.

10. Confidence Intervals and Precision

The unadjusted risk-difference estimate is -0.068, with a confidence interval from -0.161 to 0.025. The interval includes zero, the value corresponding to no absolute difference. It also spans estimates on either side of zero, so the posted event counts do not pin down the direction of the underlying difference with high precision. The unadjusted p-value is 0.152, consistent with the interval’s inclusion of the no-difference value under the corresponding analysis.

A confidence interval conveys sampling uncertainty under the assumptions of the method used. It is not a range containing every plausible explanation, and it does not account automatically for bias, measurement problems, missing data, or model misspecification. The registry record does not report enough information to evaluate those sources of uncertainty fully.

The relative recalculations also have intervals that include their no-association reference value: the risk ratio is 0.864, with an interval from 0.706 to 1.056, and the odds ratio is 0.76, with an interval from 0.522 to 1.106. The sponsor-reported Cox estimate has a 95% confidence interval from 0.58 to 0.99. That interval lies below 1, the no-hazard-ratio-difference reference value, and the registry reports p <0.05. These intervals refer to different statistical measures and should not be read as if they were estimates of the same quantity.

The distinction between the count-based estimates and the Cox estimate matters for precision as well as interpretation. One uses the observed event counts, while the other uses time-to-event regression. The registry record does not include the full analysis details needed to explain the degree to which timing, censoring, or model choices contributed to the reported precision.

11. Planning a Similar Trial: Sample Size

This is a planning illustration, not a re-evaluation of the original trial. It asks: if a new study wanted to detect a difference like the one observed, or a smaller one, how large would it need to be? It is deliberately not “observed power” of the finished trial, which is not a meaningful quantity.

The planning figures are participants per arm for 80% power and participants per arm for 90% power. They are based on two-sided significance level 0.05, equal allocation between the two arms, and a normal approximation. The effect to detect is set as a stated fraction of the observed effect. For this binary endpoint, the figures are participants per arm, not total events. The original trial’s design assumptions and sample-size justification are not reported in the registry record.

The 80% power column describes the planning sample size under which a study would have an 80% chance of detecting the specified effect at the stated significance level, if the planning assumptions hold. The 90% power column uses a higher chance of detecting that effect and therefore requires a larger planned sample size in the posted illustrations. These are planning concepts, not guarantees about the outcome of a future study.

The rows labeled 100% of the observed effect, 75% of the observed effect, and 50% of the observed effect use progressively smaller target effects. Smaller effects are harder to distinguish from random variation, so they require more participants under the stated assumptions. For example, planning for 75% of the observed effect gives 1,496 participants per arm for 80% power and 2,002 participants per arm for 90% power. Planning for 50% of the observed effect gives 3,372 participants per arm for 80% power and 4,514 participants per arm for 90% power. These illustrations are not observed power and do not describe the trial’s original design.

12. How the Sample Size Is Derived

Power is the probability that a study of a given size rejects the null hypothesis when a specific true effect exists. It depends on four things: the effect to detect, the variability of the outcome, the significance level (here a two-sided α of 0.05, so z_1−α/2 = 1.960) and the desired power (z_1−β = 0.842 for 80% and 1.282 for 90%).

Formula

n is the number of participants in each arm, p₀ and p₁ are the control and treatment proportions, and p̄ is their average.

Worked calculation for this trial

1. Control proportion p₀ = 0.500; treatment proportion p₁ = 0.432; average p̄ = 0.466.
2. First term: z_1−α/2 × √[2p̄(1−p̄)] = 1.96 × 0.7055 = 1.3827.
3. Second term: z_1−β × √[p₀(1−p₀) + p₁(1−p₁)] = 0.842 × 0.7038 = 0.5923.
4. n = (1.3827 + 0.5923)² / (-0.0682)² = 839.1, rounded up to 840 participants per arm for 80% power.

The smaller-effect rows in the table above repeat the same calculation with the effect multiplied by 0.75 and 0.5 (for ratios, applied to the logarithm of the ratio).

R code

alpha <- 0.05
z_a   <- qnorm(1 - alpha / 2)          # two-sided
p0 <- 0.5                          # control proportion
p1 <- 0.431818181818182                          # treatment proportion
n_per_arm <- function(power, frac = 1) {
  q1 <- p0 + (p1 - p0) * frac               # smaller effect = fraction of the observed difference
  pbar <- (p0 + q1) / 2
  z_b <- qnorm(power)
  ceiling(round((z_a * sqrt(2 * pbar * (1 - pbar)) + z_b * sqrt(p0 * (1 - p0) + q1 * (1 - q1)))^2 / (q1 - p0)^2, 6))
}
for (f in c(1, 0.75, 0.5))
  cat(sprintf("%3.0f%% of observed effect: n per arm = %s (80%% power), %s (90%% power)\n", 100 * f,
              format(n_per_arm(0.80, f), big.mark = ","), format(n_per_arm(0.90, f), big.mark = ",")))

# Check against R's built-in function (unrounded n per arm)
cat("power.prop.test:", round(power.prop.test(p1 = p0, p2 = p1, power = 0.80)$n, 1), "\n")

# Simulation: how often does the z-test reject at the 80%-power sample size?
set.seed(405821)
n    <- n_per_arm(0.80)
reps <- 20000
x0 <- rbinom(reps, n, p0); x1 <- rbinom(reps, n, p1)
ph <- (x0 + x1) / (2 * n)
z  <- ((x1 - x0) / n) / sqrt(ph * (1 - ph) * 2 / n)
cat(sprintf("Simulated power at n = %s per arm: %.3f (%d replicates)\n", format(n, big.mark = ","), mean(abs(z) > z_a, na.rm = TRUE), reps))

Output from running the code

100% of observed effect: n per arm = 840 (80% power), 1,123 (90% power)
 75% of observed effect: n per arm = 1,496 (80% power), 2,002 (90% power)
 50% of observed effect: n per arm = 3,372 (80% power), 4,514 (90% power)
power.prop.test: 839.1 
Simulated power at n = 840 per arm: 0.796 (20000 replicates)

The simulation draws many pairs of event counts at the planned sample size and counts how often the two-proportion z-test rejects the null. It should land close to the target power; at very small required sample sizes it can fall below it, because the normal approximation is rough there.

13. Analyses Reported by the Sponsor

The registry’s own analysis is a regression-based Cox analysis. It reports a hazard ratio of 0.75, a 95% confidence interval from 0.58 to 0.99, and p <0.05. That is the sponsor-reported time-to-event result. The simple recalculation from the posted event counts is different in form: it gives an unadjusted risk difference of -0.068, with a confidence interval from -0.161 to 0.025 and an unadjusted p-value of 0.152.

The Cox hazard ratio uses event timing, while the recalculated risk difference compares the observed group counts without modeling time to event. The two results are therefore not direct substitutes, and their p-values do not represent the same analysis. The registry record does not provide enough detail to reproduce the Cox model or identify why its inference differs from the unadjusted count-based calculation. The sponsor’s reported analysis should be read as the trial’s own analysis; the unadjusted recalculation is a separate descriptive check based on the posted summaries.

14. Multiplicity, Missing Data and Analysis Populations

The registry lists six outcome measures, five secondary outcomes, and three analyses. The primary endpoint is progression to AIDS, while the listed secondary outcomes include genital ulcer episodes, HIV-1 viral load, toxicity, adherence, and virologic and immunologic responses to antiretroviral therapy among participants who progressed to CD4+ below 250 cells per microliter. The registry record does not report how the analyses were prioritized beyond identifying the primary endpoint, or whether any adjustment for multiple comparisons was planned or applied.

Multiplicity arises when several outcomes, timepoints, subgroups, or statistical tests are examined. With more analyses, the chance of obtaining at least one result that appears statistically notable by chance can increase. Whether and how to adjust depends on the prespecified testing strategy and the purpose of the analyses. Those details are not reported in the registry record, so the secondary results should not be treated as a single confirmatory family or assumed to have multiplicity control.

The primary outcome description refers to an intention-to-treat analysis of all subjects randomized on the trial meeting the primary endpoint. The record does not explain how participants without a known endpoint status were handled, whether all randomized participants were included in each analysis, or how missing observations were addressed. It also does not provide details on withdrawals, loss to follow-up, censoring, or the number of participants with complete outcome information.

The registry record does not report a detailed analysis plan, covariate adjustment strategy, subgroup analysis plan, or interim monitoring procedures. These omissions do not establish that such procedures were absent; they mean that their use and role cannot be determined from the registry record. Interpretation should distinguish what is explicitly reported—the endpoint definition, counts, and stated analyses—from methodological details that are unavailable.

15. 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 5% reporting threshold.

Most frequent serious adverse event terms

Most frequent non-serious adverse event terms

Serious events with the highest arm-level rate: pregnancy (18.6%), malaria (11.8%), anemia (5.9%), pulmonary tuberculosis (5.9%), febrile illness, unspecified (2.3%).

The registry reports serious adverse events in 75 of 220 participants in the acyclovir group and 85 of 220 participants in the placebo group. It also reports other adverse events in 219 of 220 participants assigned acyclovir and 218 of 220 assigned placebo. These are counts of affected participants in the recorded groups; they are not counts of individual event episodes, and they do not by themselves establish that an event was caused by the assigned treatment.

The listed serious adverse event terms and percentages are pregnancy at 18.6%, malaria at 11.8%, anemia at 5.9%, pulmonary tuberculosis at 5.9%, febrile illness, unspecified, at 2.3%, and pregnancy complication, unspecified, at 2.3%. The registry record does not give the denominator or further context for those term-specific percentages in the available summary, so they should be read as reported rather than reinterpreted as participant-level risks.

Death counts are not reported in the registry record. The adverse-event figures are descriptive safety data. Their interpretation also depends on how events were defined, collected, attributed, and followed, details that are not reported in the registry record.

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

The observed event counts were 95 participants in the acyclovir arm and 110 in the placebo arm, with 220 participants in each group. The unadjusted count-based estimate was a risk difference of -0.068, and its confidence interval from -0.161 to 0.025 includes zero. The recalculated risk ratio and odds ratio also have intervals that include their no-association reference values. These summaries indicate uncertainty in the unadjusted comparison.

The registry’s own Cox analysis reports a hazard ratio of 0.75 with a 95% confidence interval from 0.58 to 0.99 and p <0.05. This analysis uses time-to-event methods and is not equivalent to the unadjusted comparison of event counts. The registry record does not provide enough detail to fully reconcile the different analyses. Readers should keep the measure, method, and associated uncertainty attached to each estimate.

The findings concern a defined population—people co-infected with HIV-1 and HSV-2 in Uganda—and a particular endpoint over 2 years. The endpoint combines a CD4+ threshold with a clinical disease criterion and excludes esophageal candidiasis from the Stage IV criterion. The results do not directly address every possible HIV outcome, every HSV-2 outcome, or populations outside the study’s stated setting.

These statistics describe the posted trial results; they do not establish that acyclovir should or should not be used. The registry record does not provide complete information on missing-data handling, model specification, or multiplicity procedures, and the secondary outcomes are not detailed in the posted results. Such gaps limit how comprehensively the overall evidence can be assessed from this record alone.

17. Why This Trial Matters Statistically

This trial is statistically informative because it reports both participant-level event counts and a time-to-event analysis for the primary AIDS-progression endpoint. Those approaches answer related but different questions. Comparing counts gives an unadjusted risk difference and relative measures, while Cox regression uses event timing. Putting both results in view helps readers avoid treating a hazard ratio as though it were a risk difference or assuming that analyses with different estimands must agree.

The uncertainty is also important. The unadjusted risk-difference interval includes zero, whereas the reported Cox-model interval lies below 1. This contrast illustrates why a result should be interpreted through its method and confidence interval, rather than by relying on a single thresholded p-value. It also shows the limits of reconstructing an analysis from summary counts: event timing and model details are not captured by the counts alone.

The endpoint illustrates a further statistical consideration. It combines an immunologic threshold and a clinical disease criterion, with a stated exclusion. A composite endpoint can capture more than one type of progression, but its interpretation depends on knowing exactly which events qualify. Here, the registry provides that definition, allowing the outcome to be understood more specifically than a broad label such as AIDS progression.

Finally, the record illustrates the distinction between trial planning and post hoc planning illustrations. The posted sample-size figures use fractions of the observed effect under stated assumptions, but they do not reveal the original trial’s design rationale. This distinction matters when using trial results to think about future study sizes: planning values are conditional illustrations, not evidence about what the completed study was designed to detect.

18. 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 gives the primary endpoint counts and a reported Cox estimate, but it does not include the full statistical analysis plan or enough model detail to reproduce the sponsor’s analysis. The handling of censoring, missing outcomes, withdrawals, and follow-up is not reported. These omissions make it difficult to assess how the time-to-event estimate was constructed and how sensitive it may be to analysis choices.

The primary outcome is a composite definition involving CD4+ below 250 cells per microliter or World Health Organization Stage IV disease, excluding esophageal candidiasis. The summary does not report separate results for the laboratory and clinical components. The reported total therefore cannot show whether one component contributed more than the other to the overall endpoint.

The registry lists secondary outcomes but the record summarized in the posted results does not give their detailed estimates. It also does not report subgroup results, the prespecified approach to multiple comparisons, or interim analysis procedures. The serious adverse-event summary gives counts and selected terms, but the record does not provide further details on event attribution or the term-specific percentage denominators. Death counts are not reported in the registry record.

The study population and setting are specifically described as people co-infected with HIV-1 and HSV-2 in Uganda, and the primary endpoint timeframe is 2 years. The record does not provide enough information to judge how participant characteristics or follow-up might affect applicability to other populations or settings. The original sample-size justification is also not reported in the registry record, so the planning illustrations should not be mistaken for the assumptions used to design the completed trial.

19. Related Tutorials

20. Related Statistical Calculators

21. Sources

• ClinicalTrials.gov: Acyclovir to Treat Patients Co-infected With HIV and Herpes Viruses in Uganda — NCT00405821.
• Registry record last updated 2012-09-28; status last verified 2012-08.
• Results first posted 2012-09-28.
• 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.

22. Record Summary

NCT00405821 is a completed Phase 2 randomized, parallel-group, placebo-controlled trial of acyclovir prophylaxis among people co-infected with HIV-1 and HSV-2 in Uganda. The registry records quadruple masking and enrollment of 440 participants, with 220 assigned to each arm. The primary endpoint was progression to AIDS over 2 years, defined by CD4+ below 250 cells per microliter or World Health Organization Stage IV disease, excluding esophageal candidiasis.

The posted counts were 95 endpoint events with acyclovir and 110 with placebo. The unadjusted risk-difference estimate was -0.068, with a confidence interval from -0.161 to 0.025 and p = 0.152. The registry’s Cox analysis reported a hazard ratio of 0.75, a 95% confidence interval from 0.58 to 0.99, and p <0.05. These are distinct analyses with different statistical measures. Several methodological details, including the original sample-size rationale and missing-data handling, are not reported in the registry record.