Abstract
After 1 year of follow-up, patients on HAART with a baseline viral load (VL) of <20 copies/ml showed significantly lower odds of virological rebound to two consecutive VLs of >50 copies/ml than those with baseline VLs of 20 to 39 and 40 to 49 (P < 0.001). The time to virological rebound was also significantly shorter (P < 0.001) for the groups with baseline VLs of 20 to 39 and 40 to 49.
TEXT
The number of patients failing antiretroviral treatment with low-level viremia (e.g., a viral load [VL] ranging from 40 to 1,000 copies/ml) is increasing (1, 2), and special interest has been shown in the clinical significance of this finding. During the last years of the past decade, commercial assays for measuring viral loads reduced their detection limits (3–6), which shifted from 50 to 40 to 20 copies/ml, depending on the assay (7). Recently, a number of reports (8–12) have focused on the clinical significance of very low-level viremia (e.g., viral-load levels below 20 or between 20 and 50 copies/ml). The use of different assays or a different sample size, and even different baseline characteristics of the studies, may partially explain some of the contradictory findings of the studies. In addition, high variability of the Cobas Ampliprep/Cobas TaqMan v2.0 assay at levels of 20 and 40 HIV copies/ml has been described (13).
Since the introduction in our institution of Cobas TaqMan v2.0 (Roche Diagnostics) in June 2009, the lower detection cutoff of 50 copies/ml was shifted to 20 copies/ml, and this new threshold was reported to physicians treating HIV and thus used for making clinical decisions.
In this retrospective cohort study, we have investigated the clinical significance of having a viral load between 20 and 50 copies/ml in terms of the odds for a viral-load rebound to more than 50 copies/ml or 400 copies/ml 1 year after testing. When possible, the emergence of resistance was also investigated.
All adult HIV patients (>18 years old) who were on highly active antiretroviral therapy (HAART) with an available follow-up 12 months (median, 12.42 months; interquartile range [IQR], 11.73 to 13.80 months) after a viral-load test result below 50 copies/ml (time zero [T0]) using the Cobas TaqMan v2.0 assay were included. When needed, resistance testing of very low-level viral loads was performed using a concentration step (14) prior to following the standard procedure of the Trugene HIV genotyping kit (Siemens NAD). Two hundred ninety patients met the inclusion criteria, and the pre-T0 CD4 count, time (in years) with a VL of <50 before T0, number of years on HAART, and type of HAART regimen were retrieved from their medical records. Virological rebound was considered when two consecutive viral loads were recorded. Two definitions of virological rebound were evaluated: (i) rebound to more than 50 copies/ml, confirmed in two consecutive samples, and (ii) rebound to more than 400 copies/ml, also confirmed in two consecutive samples. The time to virological rebound in months was also recorded. The baseline characteristics were compared using the Kruskal-Wallis test for continuous outcomes and the χ2 or Fisher exact test for categorical outcomes. Factors associated with rebound were identified in Cox proportional-hazards models. The time to virological failure was assessed with a Kaplan-Meier estimate.
Patients were stratified according to their T0 viral loads into three groups: 134 (46.2%) patients had <20 copies/ml, 94 (32.4%) patients had viral-load levels between 20 and 39 copies/ml, and 62 (21.4%) patients had viral load levels ranging from 40 to 49 copies/ml. The demographics and viral and clinical features of the studied population are shown in Table 1. Of note, the population with <20 copies/ml had been significantly suppressed for a longer time (pre-T0 suppression) than the other two groups (P < 0.0001) and had also been on HAART for a significantly longer period (P = 0.006). No other differences in baseline characteristics were observed.
Table 1.
Demographics and viral and clinical features of the studied population
| Parametera | Value for copies/ml: |
P | ||
|---|---|---|---|---|
| <20 (n = 134) | 20–39 (n = 94) | 40–49 (n = 62) | ||
| Yr with VL of <50 copies/ml pre-T0 [median (IQR)] | 3.5 (1.42–5.17) | 1.2 (0.25–4.08) | 1.1 (0.21–3.12) | <0.0001 |
| Yr of HAART [median (IQR)] | 10.5 (6.03–13.81) | 7.6 (3.05–12.86) | 8.3 (2.19–12.58) | 0.006 |
| Age (yr) [median (IQR)] | 47 (43.75–52) | 46 (43–50.25) | 47 (41–51.25) | 0.462 |
| No. (%) male | 88 (65.7) | 70 (74.5) | 50 (80.6) | 0.074 |
| CD4 count (cells/μl) [median (IQR)] | 645 (448.5–875) | 626 (379–894.25) | 596 (414.5–946) | 0.760 |
| No. (%) on HAART regimen | ||||
| 2 NRTI + NNRTI | 60 (44.8) | 34 (36.2) | 24 (38.7) | 0.232 |
| 2 NRTI + PI/r | 28 (20.9) | 20 (21.3) | 19 (30.6) | 0.492 |
| PI monotherapy | 26 (19.4) | 15 (15.9) | 10 (16.1) | 0.546 |
| Raltegravir/maraviroc | 14 (10.4) | 20 (21.3) | 9 (14.5) | 0.073 |
| Bitherapy/other | 6 (4.4) | 5 (5.3) | 0 | 0.821 |
NRTI, nucleoside reverse transcriptase inhibitors; NNRTI, nonnucleoside reverse transcriptase inhibitors; PI/r, ritonavir-boosted protease inhibitor.
Overall, after 1 year of follow-up, 2.2% (3/134) of the patients in the group with a T0 VL of <20 showed a confirmed virological rebound to >50 copies/ml, whereas 20.2% (19/94) of those with a T0 VL of 20 to 39 and 24.2% (15/62) of those with a T0 VL of 40 to 49 showed two consecutive VLs of >50 copies/ml (P < 0.001 for comparison with the group with a T0 VL of <20). The median time (in months) between the two consecutive VLs of >50 copies/ml was 2.67 (IQR, 1.26 to 3.27).
The time to virological failure was also significantly shorter (P < 0.001; Kaplan-Meier estimate) for the groups with T0 VLs of 20 to 39 and 40 to 49 (Fig. 1). Multivariate analysis (Table 2) showed that the T0 VL group (P = 0.009) and the time (in years) with a VL of <50 copies/ml pre-T0 (P = 0.005) were independent predictors of confirmed virological rebound to more than 50 copies/ml. Patients in the group with a T0 VL of 40 to 49 had a hazard ratio (HR) of 10.39 (95% confidence interval [CI], 2.24 to 48.23), and patients with a T0 VL of 20 to 39 had an HR of 9.49 (95% CI, 2.16 to 41.62) for an increased risk of experiencing a virological rebound to more than 50 copies/ml after 1 year of follow-up. Pre-T0 suppression independently lowered the risk of virological rebound to 32% (95% CI, 0.52 to 0.89).
Fig 1.
Kaplan-Meier estimate showing that time to virological rebound was significantly shorter (P < 0.001) for the groups with T0 VLs of 20 to 39 and 40 to 49.
Table 2.
Univariate and multivariate analyses showing the odds of confirmed virological rebound to >50 copies/ml
| Parametera | Univariate analysis |
Multivariate analysis |
||||
|---|---|---|---|---|---|---|
| HR | 95% CI | P | HR | 95% CI | P | |
| VL group (T0) | <0.0001 | 0.010 | ||||
| 40–49 | 13.49 | 3.89–46.81 | 10.39 | 2.24–48.23 | ||
| 20–39 | 9.06 | 2.67–30.66 | 9.49 | 2.16–41.62 | ||
| <20 | 1 | 1 | ||||
| Time (yr) with a VL of <50 copies/ml pre-T0 | 0.56 | 0.43–0.73 | <0.0001 | 0.68 | 0.52–0.89 | 0.009 |
| Time (yr) since starting HAART | 0.92 | 0.86–0.98 | 0.007 | 0.99 | 0.92–1.06 | 0.851 |
| Baseline CD4 count (cells/μl) | 0.99 | 0.99–1.00 | 0.024 | 0.99 | 0.99–1.00 | 0.369 |
| Age | 0.99 | 0.96–1.03 | 0.79 | 0.99 | 0.96–1.03 | 0.642 |
| Sex | ||||||
| Male | 2.35 | 1.02–5.45 | 0.04 | 1.47 | 0.60–3.61 | 0.357 |
| Female | 1 | 1 | ||||
| HAART regimen | 0.009 | 0.333 | ||||
| NNRTI based | 0.31 | 0.13–2.77 | 0.51 | 0.20–1.29 | ||
| Other | 1.23 | 0.54–2.77 | 1.26 | 0.51–3.11 | ||
| PI based | 1 | 1 | ||||
The T0 VL group (P = 0.009) and the time (in years) with a VL of <50 copies/ml pre-T0 (P = 0.005) were independent predictors of rebound.
When confirmed virological rebound to more than 400 copies/ml was evaluated, we found that after 1 year of follow-up, 2.2% (3/134) of the patients in the group with a T0 VL of <20, 4.2% (4/94) in the group with a T0 VL of 20 to 39, and 8.1% (5/62) in the group with a T0 VL of 40 to 49 showed two consecutive VLs of >400 copies/ml (P = 0.118).
Resistance testing was available for 8 of the 12 patients with more than 400 copies/ml. Resistance-associated mutations were detected in 4 of 8 patients. Baseline resistance was also available for these patients: in one patient, no new mutations from baseline were detected (baseline and failure: V179D, M184I, and G190R); another patient with baseline resistance (M41L, A62V, D67N, and T215Y) added V179I, M184V, L210W, and K219N mutations while on a DRVr-3TC-ETV (boosted darunavir-lamivudine-etravirine) regimen, and the other two patients added V179D (on a DRVr monotherapy regimen) and Y181N (on a TDF-FTC-ATZr [tenofovir-emtricitabine-boosted atazanavir] regimen) to a wild-type baseline virus.
Doyle et al. (8), using the Abbott Real Time HIV-1 VL assay, have shown that patients with viral loads ranging from 40 to 49 are at an increased risk of virological rebound to >50 and >400 copies/ml. Maggiolo et al. (9), using an ultrasensitive version of the Siemens assay, have shown similar results. Henrich et al. (12) have recently presented data on the use of Cobas TaqMan v2.0 in the United States, with a 22-month period of follow-up, finding increased hazard ratios for viral rebound to >50 and >400 copies/ml for patients with less than 48 copies/ml but with detectable RNA compared to patients with no detectable RNA. Cobas TaqMan v2.0 is widely used across Europe, so there was a need for us to verify their findings with the commonly used <20-copy/ml cutoff.
We failed to find any association with a confirmed viral rebound to >400 copies/ml. As in other studies (10, 11), our results may be underpowered by the sample size, which we consider the main limitation of our study. Thus, we were not able to reproduce previous results when a confirmed virological rebound to >400 copies/ml was investigated. Charpentier et al. (10) also failed to find any association with a virological rebound to more than 50 copies/ml; the number of patients studied (38 with viral loads between 20 and 49 copies/ml versus 618 below 20 copies/ml) and a different study design (a longitudinal study with at least three HIV-1 RNA determinations over a 1-year period) may have been responsible for this lack of association. Similarly, investigators from the Swiss Cohort (11) also failed to find any association between very low-level viremia (20 to 49 copies/ml) and virological failure, but again, the sample size (only 26 patients with viral loads between 21 and 49 copies/ml) may be responsible for this. Another limitation of our study may be the high variation described by other authors for the viral-load assay (13), so virological rebound as defined in this study could then be due to assay imprecision.
In summary, we present data confirming that, using Cobas TaqMan v2.0, patients with a viral load ranging from 20 to 49 copies/ml have a higher likelihood of subsequent virological rebound to >50 copies/ml. We also have shown that in these patients virological rebound occurs in a significantly shorter time. Special care should be taken with these patients; factors such as adherence, the potency and genetic barrier of the regimen, drug levels, time with a viral load below 50 copies/ml, history of treatment, or even immune activation markers should be carefully evaluated to support any clinical decision.
ACKNOWLEDGMENTS
We acknowledge funding by Consejería de Salud, Convocatoria de Intensificación de la Actividad Investigadora-2012 and PI-0123/2010; by Red Temática Cooperativa de Investigación en SIDA (FISss-ISCIIIRETIC0006/0016); and by Convocatoria de Investigación Independiente, Ministerio de Sanidad (EC11-001).
Footnotes
Published ahead of print 6 February 2013
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