There is an ongoing debate concerning the level of plasma HIV RNA which warrants a change in antiretroviral combination among HIV-1-infected patients [1,2]. In theory, the goal of treatment is to maintain plasma HIV RNA level below detectable levels, with the aim of limiting the acquisition of drug resistance . To reach this goal, current recommendations encourage systematic changing of treatment in patients with at least two detectable HIV RNA measurements . This action is nevertheless not easy to achieve in clinical practice as repeated changes of antiretroviral regimens may reduce future treatment options . Data from observational cohorts of treated patients may help to define a level of HIV RNA above which treatment changes are required or below which the necessity for change remain questionable. Our objective was to compare clinical disease progression according to HIV RNA evolution in the year following initiation of a new antiretroviral treatment. HIV RNA response was studied using two different approaches: (i) taking into account HIV RNA levels measured after 4 months, the usual time period used to allow the clinician to evaluate the effectiveness of a new treatment ; and (ii) the initial viral response in the first month following initiation of treatment.
The Aquitaine Cohort is a prospective hospital-based cohort of HIV-1-infected patients under routine clinical management , initiated in 1987 in the Bordeaux University Hospital and four other public hospitals in Aquitaine by the Groupe d'Epidémiologie Clinique du Sida en Aquitaine (GECSA). Inclusion criteria were: all adults who were in- or out-patients of the participating hospital wards with HIV-1 infection confirmed by Western blot testing, regardless of clinical stage, either having at least one follow-up after the first report or with a known date of death, and having given informed consent. To be included in the present study, patients of the Aquitaine Cohort were required to have initiated between 1996 and 30 July 1997 a dual nucleoside analogues regimen or a triple-drug combination (two nucleoside analogues and one protease inhibitor). The patients should have at least two measures of CD4+ cell count and HIV RNA between 4 and 12 months after the initiation of the dual- or triple-drug combination. One of these two measurements had to be performed between 10 and 14 months of follow-up. Patients were excluded if antiretroviral treatment had been prescribed before inclusion in the cohort or during the acute phase of HIV infection.
CD4+ cell count was measured by flow cytometry. Ninety per cent of plasma HIV-1 RNA measures were performed using branched DNA assay (Chiron Quantiplex RNA HIV-1, Emeryville, California, USA) with a lower limit of quantification of this assay of 2.7 log10 copies/ml (500 copies/ml); 10% were performed using more sensitive assays (with a lower limit of detection of 1.3 or 1.7 log10 copies/ml).
The baseline of the prognostic study was 12 months following the initiation of antiretroviral combination (Fig. 1).
Patients were classified on the basis of the evolution of HIV-RNA between 4 and 12 months after the initiation of the treatment: (i) good responders (R+) were those with all, or all but one, measurements remaining below 2.7 log10 copies/ml; (ii) intermediate responders (R+/−) were those with at least two measurements above 2.7 log10 copies/ml but never twice above 3.7 log10 copies/ml; (iii) poor responders (R−) were those with at least two measurements above 3.7 log10 copies/ml. Calculation of the area under the curves of the evolution of HIV RNA in these three groups was performed using a cubic-spline method .
Risk of disease progression after 12 months following initiation of antiretroviral treatment was estimated using a proportional hazards regression model. Survival time was the interval between the entry date (12 months after initiation of a new antiretroviral regimen) and a new AIDS-defining event according to the CDC 1993 criteria or death or last follow-up. Patients who did not experience any new AIDS-defining event and were still alive on 31 December 1998 were right censored on the date of their last assessment. The proportional hazards assumption was checked by examining log [−log (survival probability)] versus time and by testing the interaction between covariate and log(time). Models were adjusted for covariates measured at the initiation of antiretroviral treatment (gender, age, HIV transmission group, CD4+ cell count, history of antiretroviral treatment, date of initiation of treatment, type of antiretroviral combination), variables measured during the first 12 months after inception of antiretroviral treatment (change of two or more antiretroviral drug, AIDS-defining event, type of viral response) and CD4+ cell count after 12 months of treatment. Those reaching the 0.25 level of significance in univariate analysis were included in multivariate analysis (model 1). To take into account the initial viral response to treatment, the variable `at least one undetectable HIV RNA during the initial 4-month period' was added. This additional analysis was performed on a sub-sample as data were not available for all patients.
We further studied the prognostic value of all serial HIV RNA measurements, including initial viral response, distinguishing two periods with a cutoff at 1 month as suggested in some therapeutic guidelines . Reductions of HIV RNA were estimated using a mixed model which took into account the left censoring of undetectable viral load. This method is a full likelihood approach for analysis of left-censored longitudinal data . HIV RNA under the detection limit contributed as censored observations and not as values equal to the limit. The model included one intercept and two slopes in fixed and random effects assuming individual variations of the baseline HIV RNA and the slopes. The first slope estimated the reduction of HIV RNA during the first month and the second slope the reduction during the 2–12 month period. The prognostic values of estimated initial HIV RNA level and reduction during and after the first month were evaluated as continuous variables in model 2.
The relationship between the viral response during the 4–12 month period as defined in model 1 and the viral response within the first month estimated by the mixed model was explored. First, mean HIV RNA reductions by 1 month were described according to categories of subsequent responders (R+, R+/−, R−) and compared using a Kruskal–Wallis test. Then, to allow a more practical interpretation, the same comparison was performed using a reduction of HIV RNA by 1 month dichotomized at the 0.5 log10 copies/ml threshold as suggested in clinical guidelines .
Among 1415 patients who initiated treatment with a dual or a triple antiretroviral regimen between 1996 and 30 June 1997, 773 (55%) were included in the study sample. The other 642 patients were excluded because of a lack of CD4+ cell count or HIV RNA measurements. They were comparable with the study sample for age, gender, and HIV clinical stage. However, they were more often intravenous drug users (35 versus 26% among included patients, P = 0.001) and more often treated initially with a dual drug treatment (59 versus 53%, P = 0.004). Characteristics of the study sample at the initiation of antiretroviral combination are shown in Table 1. The most common triple drug combinations were zidovudine–lamivudine–indinavir (91 patients) and stavudine–lamivudine–indinavir (62 patients). For initial dual drug treatment, the most common regimens were zidovudine–didanosine (159 patients) and zidovudine–zalcitabine (145 patients). During the first 12 months, 274 (35%) patients had at least two drugs changed in their regimen. Frequency of treatment changes was the same for patients treated with dual or triple drug treatments (33 versus 39%, P = 0.09). Median follow-up was 14.5 months [interquartile range (IQR), 9.0–18.6] after baseline and 27 months (IQR, 22.0–31.1) after starting a new antiretroviral treatment. Only 28 (3.7%) patients were considered lost to follow-up because their last follow-up occurred more than 12 months prior to 31 December 1998.
During the study of disease progression (after the first 12 months), 14 patients died and 48 experienced 53 AIDS-defining events. AIDS-defining events were oesophagal candidiasis (11), cytomegalovirus infection (eight), cutaneous Kaposi's sarcoma (seven), wasting (six), Mycobacterium avium infection (four), cryptococcosis (three), lymphoma (three), pulmonary tuberculosis (two), recurrent pneumonia (two), toxoplasmosis (two), HIV-associated dementia (two), Pneumocystis carinii pneumonia (one), cryptosporidiosis (one), chronic herpes infection (one).
Three hundred and fifty-three patients (45%) were classified as R+, 199 (26%) as R+/− and 221 (29%) as R− (Table 2). Viral response measured by the area under the curve differed between the three groups: 886 days × log10 copies/ml for R+, 1078 for R+/− and 1319 for R− (P < 10−3). During the first year of treatment, 18% of R− experienced an AIDS-defining condition versus 7% of R+/− and 8% of R+ (P < 0.001). Also, R− had changed their treatment more often (62%) than R+/− (29%) and R+ (23%, overall P value < 0.001).
In the univariate analysis, the category of viral response during the 4–12 month period after initiation of antiretroviral combination was associated with the subsequent occurrence of an AIDS-defining event or death. AIDS-free survival was 97% (R+), 96% (R+/−) and 86% (R−) respectively (overall P-value < 10−4). Clinical evolution between R+ and R+/− did not differ significantly (P = 0.80). Other variables associated with a higher risk of disease progression were: lower CD4+ cell count at initiation of treatment, and after 12 months, most recent calendar periods of treatment initiation, antiretroviral pre-treated status, triple drug treatment, change of treatment and an AIDS-defining diagnosis during the 0–12 months period (Table 3). In the multivariate analysis, the category of viral response remained significantly associated with poorer outcome as R− more often experienced an AIDS-defining event or death compared with R+ [hazard ratio (HR), 2.2;P = 0.01], whereas R+/− did not (HR, 1.4;P = 0.4). Other covariates significantly associated with disease progression were CD4+ cell count at 12 months [HR, 0.7 for 100 × 106 cells/l higher; 95% confidence interval (CI), 0.5–0.9] and the onset of an AIDS-defining event during the 0–12 months period (HR, 2.3; 95% CI, 1.3–4.3).
Among 602 patients with HIV RNA measurements available during the first 4 months of follow-up, 226 (38%) had at least one measure below 2.7 log10 copies/ml. In the univariate analysis, having at least one measurement below 2.7 log10 copies/ml during the first 4 months was a protective factor of clinical evolution (HR, 0.35;P = 0.007). After adjustment for variables of model 1, this variable was no longer associated with clinical evolution (HR, 0.83;P = 0.67) and the effect of viral response during the 4–12 months period was not changed: R− were at high risk of an AIDS-defining event or death after 12 months compared with R+ (HR, 3.08;P = 0.006) and there was no statistical difference of clinical evolution between R+/− and R+ (HR, 2.04;P = 0.14).
Using a mixed model, estimation of HIV RNA level at treatment initiation was 4.32 log10 copies/ml (95% CI, 4.21–4.42). The estimation of HIV RNA yielded a reduction of 1.10 log10 copies/ml within the first 30 days of antiretroviral treatment (95% CI, −1.22 to −0.98) and −0.15 log10 copies/ml for the subsequent 11 months (95% CI, −0.20 to −0.10). Adjusting for all covariates, the individual estimations of HIV RNA reduction before and after 1 month of antiretroviral combination were significantly associated with disease progression after 12 months (Table 4). HIV RNA level at the initiation of antiretroviral treatment did not remain associated with disease progression after adjustment for virological response (P = 0.60).
Medians of HIV RNA reduction by 1 month significantly differed according to the subsequent responder status: 2.02 log10 copies/ml among R+, 1.32 log10 copies/ml among R+/−, 0.59 log10 copies/ml among R− (P < 10−4). The responder status between 4 and 12 months was also significantly (P < 10−4) associated with the initial viral reduction taken as a dichotomous variable using the recommended threshold 0.5 log10 copies/ml: 98% of subjects with an initial viral reduction lower than 0.5 log10 copies/ml were subsequently classified as poor responders (Table 5).
In a large multi-risk cohort of HIV-1 patients, sustained HIV RNA over 3.7 log10 copies/ml between 4 and 12 months after initiation of antiretroviral treatment is a major prognostic factor of clinical disease progression. This situation therefore requires a prompt change of antiretroviral combination. Part of our analysis focused on the prognostic value of the level above which HIV RNA is sustained because the risk of clinical progression of patients with intermediate levels of detectable HIV RNA is not well documented. Patients who maintained detectable HIV RNA below 3.7 log10 copies/ml have no significant increase of clinical progression after 12 months compared with those who maintained HIV RNA below 2.7 log10 copies/ml regardless of the clinical events or changes of treatment they had experienced before. This result was not modified when adjusting for the observation of at least one undetectable HIV RNA measurement during the first 4 months of treatment. Thus, it may probably be applied not only to those who never reach undetectable levels but also to those whose viraemia was initially suppressed to undetectable levels but then become detectable again. In a study of the relation between the mean HIV-RNA during the first 8 to 52 weeks of reverse-transcriptase inhibitor treatment and disease progression, Staszewski et al. also reported a low short-term risk of progression for patients with HIV-1 RNA under 3.7 log10 copies/ml . If the clinical implications of detectable intermediate levels of HIV RNA allowed differentiation between the potential change of drug regimen, this should be argued on the basis of resistance concerns . In practice, clinicians must then take into account the clinical, biological and treatment history of the patient to decide to change an antiretroviral combination. The relevance of the 2.7 and 3.7 log10 copies/ml (500 and 5000 copies/ml) thresholds was confirmed by the increasing hazard ratio between these three categories and the relationship found with the initial viral response.
In our subsequent analyses, we found that: (i) having at least one measurement below 2.7 log10 copies/ml during the first 4 months of therapy; (ii) both reductions of HIV RNA before or after 1 month were protective factors for disease progression. The general relationship between HIV RNA and disease progression has already been demonstrated  and in particular the changes of HIV RNA over time [11,12] such as HIV RNA initial reduction after initiation of antiretroviral treatment [13–15]. However, methods to summarize measurements of HIV RNA may vary between studies, for example: mean changes in HIV RNA during 6 months , changes from baseline to week 8 [14,15], or mean of HIV RNA during the first 8 to 52 weeks of treatment . Several studies have looked at the implications of the methods used to analyse plasma HIV RNA [7,17–19]. In order to estimate the prognostic value of HIV RNA measured during the first year of treatment, we chose to use all the available information. A method accounting for repeated measurements and taking into account undetectable HIV RNA regardless of the threshold was used to estimate HIV RNA reductions. As with other methods that take into account censored HIV RNA, it avoids the classical overestimation of the true value of undetectable HIV RNA (and therefore the underestimation of the HIV RNA reduction) [7,12,19]. In our unselected cohort, estimation of the average reduction of HIV RNA during the first month after initiation of a new antiretroviral treatment was slightly lower than results that have been reported in clinical trials using methods for censored data [12,20]. Moreover, the non-significant effect of baseline HIV RNA after adjustment for reduction during the first month demonstrated that HIV RNA suppression confers a full reduction in risk for clinical progression. As the prognostic value of a slope is difficult to interpret in clinical practice, we conducted the analysis with thresholds, chosen according to treatment guidelines [1,21,22]. We thus found that a log reduction of HIV RNA of less than 0.5 by 4 weeks was highly associated with a subsequent poor viral response. The association between initial response and subsequent level of viral load corroborated the predictive value of nadir (lower HIV RNA level after initiation of antiretroviral treatment) on length of time that the HIV RNA remains suppressed by treatment . This relation allows anticipation of a poor viral response to treatment and provides the opportunity, if possible, to modify the drug regimen.
In conclusion, HIV RNA evolution several months after a new prescription of antiretroviral combination has a major prognostic role on clinical progression. An initial viral load reduction during the first month that is less than 0.5 is a strong predictor of subsequent HIV RNA evolution. Poor viral responders with several measurements above 3.7 log10 copies/ml between 4 and 12 months after initiation of treatment clearly have a poor clinical evolution. A change in the treatment regimen for intermediate responders who seem to have a moderate risk of progression must be discussed in conjunction with the patient history and the remaining number of antiretroviral combinations as short-term clinical implications are limited in comparison with patients with constant undetectable HIV RNA. Further data on drug-resistance tests and their prognostic implications on disease progression could modify these attitudes.
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Composition of the Groupe d'Epidémiologie du SIDA en Aquitaine
Organization and methodology: Prs G. Chêne, F. Dabis and R. Salamon.
Clinical coordination: Drs D. Lacoste, D. Malvy, I. Pellegrin, Prs M. Dupon, JF. Moreau, P. Morlat, JL. Pellegrin and JM. Ragnaud.
Participating Hospital Departments (participating physicians): Bordeaux University Hospital: Pr J. Beylot (Pr P. Morlat, Drs N. Bernard, F. Bonnet, D. Lacoste), Pr C. Beylot (Pr MS. Doutre), Pr C. Conri (Dr J. Constans), Pr P. Couzigou, Pr H. Fleury (Drs B. Masquelier, I. Pellegrin), Pr M. Geniaux (Mrs A. Simon), Pr JY. Lacut (Pr M. Dupon, Dr I. Chossat,), Pr JL. Pellegrin (Dr P. Mercie, Pr B. Leng), Pr M. LeBras (Drs F. Djossou, D. Malvy and JP. Pivetaud), Pr JF. Moreau (Dr JL. Taupin), Pr JM. Ragnaud (Drs C. De La Taille, H. Dutronc, D. Neau), Pr C. Series, Pr A. Taytard; Dax Hospital: Dr M. Loste (Dr I. Blanchard); Bayonne Hospital: Drs F. Bonnal and M. Ferrand (Drs Y. Blanchard, S. Farbos, MC. Gemain); Libourne Hospital: Drs J. Ceccaldi, B. Darpeix, and P. Legendre (Dr X. Jacquelin); Villeneuve-sur-Lot Hospital: Drs E. Buy and G. Brossard.
Data management and analysis: Mrs L. Dequae-Merchadou, Dr C. Marimoutou, Mr G. Palmer, Mrs D. Touchard.
Data collection: Mrs J. Caie, M. Decoin, AM. Formaggio, M. Pontgahet, B. Uwamaliya.