Thymic volume predicts CD4 T-cell decline in HIV-infected adults under prolonged treatment interruption

OBJECTIVE: To analyze the predictive capacity of thymic volume in CD4 T-cell loss after treatment interruption in HIV-infected patients with high nadir CD4 count. METHODS: Thirty-nine HIV-infected patients with CD4 counts greater than or equal to 500 cells/microL, nadir CD4 counts greater than or equal to 250 cells/microL, and plasma viral loads less than 50 copies/mL for at least the past 12 months began a treatment interruption program. The event of interest for this study was the decrease of CD4 count below 350 cells/microL. Kaplan-Meier curves were used for all time-to-event analyses, and log-rank tests were used for comparison between groups in the univariate analysis. All variables with statistical association with CD4 T-cell loss were analyzed using multivariate Cox proportional hazards regression models. RESULTS: Twenty-three percent of the patients had a decrease in CD4 count to less than 350 cells/microL. In the univariate analysis, only thymic volume was statistically significant with this event (P = 0.02). Nadir CD4 count nearly reached statistical significance. However, age, sex, HCV coinfection, CD4 count, T-cell receptor excision circle-bearing cells, and early viral load rebound did not show statistical differences. Thymic volume and CD4 T-cell loss were independently associated using Cox proportional hazards regression model (P = 0.04; relative risk, 0.76; 95% confidence interval, 0.59-0.99). CONCLUSIONS: In this study, we demonstrate for the first time that thymic volume predicts CD4 T-cell loss in patients with nadir CD4 count greater than or equal to 250 cells/muL under treatment interruption.     

Three-year durability of dual-nucleoside versus triple-nucleoside therapy in a Thai population with HIV infection

We compared the long-term immunologic and virologic efficacy of the dual- and triple-nucleoside therapy for HIV infection. This was a retrospective analysis of 2 randomized clinical trials in antiretroviral-naive patients. In the dual-nucleoside group, 15 started with didanosine (ddI) monotherapy and then added stavudine (d4T) after 24 weeks, 63 started with various doses of d4T and ddI, and 53 started with zidovudine (ZDV) and lamivudine (3TC). In the triple-nucleoside group, 53 started with ZDV, 3TC, and ddI. After 48 weeks, patients who were not failing were randomized to immediate (before treatment failure) versus delayed (at the time of virologic failure) switching from ddI and d4T to ZDV and 3TC or vice versa and from ZDV, 3TC, and ddI to d4T, 3TC, and abacavir (ABC). Failure was defined as a plasma HIV-1 RNA level>or=1 log10 above nadir or >or=10,000 copies/mL when nadir was <500 copies/mL. Patients failing therapy before week 48 received the new treatment as in the immediate switching group. Hydroxyurea was added to the last treatment regimen if patients failed after week 96. CD4 count and plasma HIV-1 RNA level (branched DNA assay with a cutoff point of 50 copies/mL) at week 144 were analyzed by intention to treat. Compared with the dual-nucleoside group, the triple-nucleoside group had a higher proportion of patients with <50 copies/mL at 144 weeks (60% vs. 18%; P<0.001), higher median CD4 count (388 cells/microL vs. 346 cells/microL; P=0.018), and longer duration of response, defined as the time from onset of viral suppression (<500 copies/mL) to the time of treatment failure (the first of 2 consecutive HIV-1 RNA measurements >500 copies/mL never followed by 2 consecutive visits showing suppressible viremia to <500 copies/mL) or discontinuation from the study (144 weeks vs. 104 weeks; P=0.002). Multivariate regression analyses showed that significant predictors for treatment success, defined as a plasma viral load <50 copies/mL at week 144, were asymptomatic clinical status at enrollment, a baseline plasma viral load 相似文献   

Antiretroviral-associated toxicity among HIV-1-seropositive pregnant women in Mozambique receiving nevirapine-based regimens

OBJECTIVE: To assess toxicities associated with highly active antiretroviral therapy (HAART) among HIV-1-infected pregnant women treated with nevirapine-based regimens according to Mozambican national guidelines. STUDY DESIGN: Prospective cohort study. METHODS: HIV-1-infected antiretroviral-naive pregnant women with CD4 counts < or =350 cells/microL were initiated on nevirapine, lamivudine, and stavudine or zidovudine and followed monthly. Severe hepatotoxicity was defined as aspartate aminotransferase (AST) or alanine aminotransferase (ALT) levels > or =5-fold the upper limit of normal. Analyses were stratified by baseline CD4 count (<250 vs. 250-350 cells/microL). RESULTS: Among 146 pregnant women, 75 (52%) began nevirapine, lamivudine, and zidovudine and 71 (48%) began nevirapine, lamivudine, and stavudine. Overall, 79 (54%) women had CD4 counts <250 cells/microL, 7 (5%) had grade II hepatotoxicity, and 4 (3%) had severe (grade III or IV) hepatotoxicity. All 4 women with severe hepatotoxicity had baseline CD4 counts > or =250 cells/microL (P = 0.02). Rates of skin toxicity, anemia, and peripheral neuropathy did not differ by CD4 cell count group. Overall, 12 (8%) women changed or discontinued HAART as a result of drug toxicity. CONCLUSIONS: Severe hepatotoxicity from nevirapine-containing HAART in this cohort of pregnant women was more common at higher CD4 counts (6% vs. 0% among women with CD4 counts > or =250 cells/microL and CD4 counts <250 cells/microL, respectively), suggesting that laboratory monitoring is necessary when administering nevirapine-containing regimens to pregnant women with CD4 counts > or =250 cells/microL.     

It is safe to stop antiretroviral therapy in patients with preantiretroviral CD4 cell counts >250 cells/microL

OBJECTIVE: To study clinical, immunologic, and virologic outcomes in patients who stop antiretroviral therapy (ART) with relatively preserved CD4 cell counts. DESIGN AND METHODS: Patients with a documented CD4 cell count >250 cells/microL who stopped ART for any reason for at least 5 weeks were studied. Relevant clinical and laboratory data were collected using a standardized data collection form. MAIN OUTCOME MEASURES: Patients were monitored for outcomes including Centers for Disease Control (CDC) category B or C events, time to restarting ART, and time to reaching a CD4 cell count of < or = 250 cells/microL. RESULTS: A total of 107 patients were included. The median time on ART was 45 months and median number of antiretroviral medications was 4. The median pre-ART CD4 cell count and HIV viral load were 463 cells/microL and 4.35 log copies/mL, respectively. The median CD4 cell at time of ART stop was 739 cell/microL. The slope of the CD4 decrease was 65 cells/mo in the first 2 months, which was greater than the subsequent decline of 8 cells/mo thereafter (P < 0.01). Similarly the median viral load increase was 2.54 log copies/mL in the first 2 months after stopping and was unchanged after that point. Two patients experienced the retroviral rebound syndrome after ART cessation but no CDC category B or C events were observed during 10 months of follow-up. The median time from stopping ART to reaching the combined endpoint of CD4 <250 or restarting ART was 8.9 months. In multivariate analysis, pre-ART CD4 cell count >250 was protective of reaching the combined endpoint (odds ratio = 0.156, P = 0.03). Other predictors of reaching the combined endpoint in multivariate analysis were older age and number of prior ART agents. Patients who restarted ART had a favorable virologic and immunologic response. CONCLUSIONS: Patients with relatively high CD4 cell counts prior to starting ART did well after stopping ART. Pre-ART CD4 cell count can be used to predict outcomes after ART cessation.     

A comparison of genital HIV-1 shedding and sexual risk behavior among Kenyan women based on eligibility for initiation of HAART according to WHO guidelines

BACKGROUND: Guidelines for initiating antiretrovirals are based on markers of advanced disease and are not directly linked to markers of HIV-1 transmission such as viral shedding. METHODS: We evaluated genital HIV-1 shedding and risk behavior among 650 antiretroviral-na?ve women stratified by WHO criteria for initiating antiretrovirals based on CD4 count and symptoms. RESULTS: Genital HIV-1 concentrations increased in stepwise fashion with declining CD4 counts and the presence of symptoms. Compared with the reference group (asymptomatic with CD4 >350 cells/microL), those with advanced immunosuppression (CD4 <200 cells/microL) had significantly higher cervical HIV-1 RNA concentrations (2.4 log10 copies/swab vs. 3.8 log10 copies/swab, P < 0.001). However, women with CD4 counts <200 cells/microL were also less likely than the reference group to report intercourse during the past week (58% vs. 26%, P < 0.001). CONCLUSIONS: Antiretroviral guidelines focusing on individuals with the most advanced immunosuppression will target those with the highest genital HIV-1 concentrations. However, individuals with less advanced immunosuppression also have high levels of genital HIV-1 and may be more sexually active. The effect of increased antiretroviral availability on the spread of HIV-1 might be enhanced by extending treatment, in addition to other risk reduction services, to those with less advanced disease.     

Short-term CD4 cell response after highly active antiretroviral therapy initiated at different times from seroconversion in 1,500 seroconverters

The effect of HIV infection duration and CD4 cell count on short-term CD4 response was evaluated in treatment-naive seroconverters using logistic regression adjusted for CD4 count before highly active antiretroviral therapy (HAART) as well as for exposure category, age, sex, acute infection, and cohort. This association was also investigated in pretreated seroconverters, further adjusting for prior therapy. CD4 response (increase of >100 cells/microL at 6 months) was more likely if HAART was initiated in the first year following seroconversion (OR = 1.50 [95% CI: 1.07-2.10] compared with 2-5 years). There was no improvement in response from initiating HAART with CD4 count >350 cells/microL compared with 201 to 350 cells/microL. Below 200 cells/microL, however, the chance of a CD4 response appeared to be reduced (OR = 0.72 [95% CI: 0.40-1.28] for 0-200 cells/microL compared with 201-350 cells/microL, P = 0.26). Results were similar for pretreated individuals. Further, in pretreated individuals, a CD4 response was less likely if the CD4 nadir was lower than the pre-HAART CD4 count (OR = 0.18 [95% CI: 0.10-0.36] for >150 cells/microL difference between nadir and pre-HAART CD4 count vs. no difference, P < 0.001). Given the limitations of observational studies, particularly the inability to control for unmeasured confounders, these findings suggest that the initiation of HAART within the first year following seroconversion appears to improve short-term immunologic response. After that time, there is little to be gained in terms of short-term response from initiating HAART before reaching a CD4 count of 200 cells/microL.     

High thymic volume is associated with viral replication and immunologic impairment only early after HAART interruption in chronic HIV infection

One of the strategies that has been investigated to reduce antiretroviral treatment toxicity in patients infected with human immunodeficiency virus (HIV) is structured treatment interruption (STI). Our aim was to analyze early viral and immune dynamics after interruption of highly active antiretroviral therapy (HAART) and to determine whether thymic function-related markers play a role in preventing CD4 count decline caused by increased viral replication. This was a prospective study of an open cohort of 47 HIV-infected patients with a median 969 CD4 count and prolonged viral suppression. They were followed every 4 weeks though week 24. Thymic volume and TREC level were analyzed at baseline. Increased thymic volume was associated with higher plasma viral load and greater CD4 count decline early after interruption. Three virologic patterns were observed: rapid/high (RH), delayed/high (DH), and low/slow (LS) viral replication. RH correlated with higher thymic volume at baseline and with higher CD4 count decline at week 4. Patients with greater thymic volume was associated with an immune and virologic impairment only early after interruption, probably because of infection of the increased number of available target cells. As the long-term consequences of these observations are unknown, the safety of treatment interruption must be further studied.     

The impact of adherence on CD4 cell count responses among HIV-infected patients

BACKGROUND: There have been concerns that irreversible immune damage may result if highly active antiretroviral therapy (HAART) is initiated after the CD4 cell count declines to below 350 cells/microL; however, the role of antiretroviral adherence on CD4 cell count responses has not been well evaluated. METHODS: We evaluated CD4 cell count responses of 1522 antiretroviral-naive patients initiating HAART who were stratified by baseline CD4 cell count (<50, 50-199, and >or=200 cells/microL) and adherence. RESULTS: Among patients starting HAART with <50 cells/microL, during the fifth 15-week period after the initiation of HAART, absolute CD4 cell counts were 200 cells/microL (interquartile range [IQR]: 130-290) for adherent patients versus 60 cells/microL (IQR: 10-130) for nonadherent patients. Similarly, among patients starting HAART with 50 to 199 cells/microL, during the fifth 15-week period after the initiation of HAART, absolute CD4 cell counts were 300 cells/microL (IQR: 180-390) versus 125 cells/microL (IQR: 40-210) for nonadherent patients. In Cox regression analyses, adherence was the strongest independent predictor of the time to a gain of >or=50 cells/microL from baseline (relative hazard [RH] = 2.88, 95% confidence interval [CI]: 2.46-3.37). Among patients with baseline CD4 cell counts <200 cells/microL, adherence was the strongest independent predictor of the time to a CD4 cell count >200 cells/microL (RH = 4.85, 95% CI: 3.15-7.47). CONCLUSIONS: These data demonstrate that substantial CD4 gains are possible among highly advanced adherent patients and should contribute to the ongoing debate over the optimal time to initiate HAART.     

Effect of long-term highly active antiretroviral therapy in restoring HIV-induced abnormal B-lymphocyte function

Although highly active antiretroviral therapy (HAART) has been reported to restore defects in cell-mediated immunity to a significant degree, little is known of its effects in restoring HIV-induced abnormal antibody-mediated immunity. We conducted a cross-sectional study of 1) 29 HIV-infected patients on chronic HAART whose HIV viral load was undetectable and whose absolute CD4+ T-lymphocyte count had been consistently sustained by > or =150 cells/microL over their pre-HAART nadir value for >1 year; and 2) 29 untreated HIV-infected patients with current CD4 counts matching the treated patients' prior nadir CD4 counts. Serum was tested for total IgG and by protein electrophoresis with immunofixation for paraproteins. Although serum IgG levels were significantly lower in patients who had received long-term virologically effective HAART than in CD4 count-matched untreated patients (1488 +/- 475 mg/dL vs. 1999 +/- 775 mg/dL, p =.004), serum IgG was still abnormally elevated in 45% of the untreated group despite a mean 28 months of HAART-induced HIV suppression and CD4 count restoration. Paraprotein spikes were confirmed by immunofixation in 7% of patients in each group. This study provides the longest reported observation to date of the effect of HAART on HIV-induced abnormal antibody-mediated immunity. Larger and longer-term studies of HAART effect on B-cell reconstitution are needed.     

Routine CD4 monitoring in HIV patients with viral suppression: Is it really necessary? A Portuguese cohort

Purpose

CD4 cell-count has been regarded as the key surrogate marker for prognostic staging and therapeutic monitoring of HIV-infected individuals. Our purpose was to assess the probability of maintaining a CD4 count >200 cells/μL in patients with continuous viral suppression and CD4 cell counts >200 cells/μL.

Predictors of sustained response to therapy resumption after treatment interruption in HIV-infected patients failing antiretroviral therapy

In order to evaluate whether a sustained virologic response to therapy resumption after treatment interruption can be achieved in the setting of virologic failure, we reviewed retrospectively the data relating to 56 human immunodeficiency virus (HIV)-infected subjects selected from 3,145 patient charts. At the time of treatment interruption (study entry), the median (interquartile range) CD4+ counts and HIV-RNA levels were respectively 247 (127-502) x 10(6) cells/L and 4.24 (3.68-5.02) log(10) copies/ml, and the patients had been exposed to eight (5-9) antiretroviral drugs. After treatment interruption, the patients received at least three drugs depending on their treatment history. Forty-eight weeks after the resumption of therapy, 19 of the 56 patients (34%) had HIV-RNA levels of <400 copies/ml and, in comparison with study entry, the difference in the median increase in CD4+ counts between the virologic responders and non-responders (83 vs. 8.5 x 10(6) cells/L) was statistically significant (P = 0.02). Multivariate analysis showed that higher peak HIV-RNA levels before treatment interruption were independently predictive of virologic failure, whereas a longer treatment interruption period independently correlated with a virologic response. Four patients with CD4+ counts of <200 x 10(6) cells/L at study entry developed HIV-related clinical events. A sustained virologic response to therapy resumption after treatment interruption can be achieved in the setting of virologic failure. An evaluation of clinical history may help to identify the patients who are more likely to respond.     

The role of hydroxyurea in enhancing the virologic control achieved through structured treatment interruption in primary HIV infection: final results from a randomized clinical trial (Pulse)

BACKGROUND: Structured treatment interruptions (STIs) have been postulated to improve virologic control in primary HIV infection (PHI) by stimulating HIV-specific T-lymphocyte immunity. The addition of hydroxyurea (HU) may reduce viral production from activated CD4 cells. METHODS: Patients with PHI received a standardized antiretroviral (ARV) regimen consisting of indinavir 800 mg twice daily (BID), ritonavir 100 mg BID, didanosine 400 mg (QD), and either stavudine 40 mg BID or lamivudine 150 mg BID, for up to 12 months and were randomized to HU 500 mg BID or not. If viral suppression (<50 copies/mL) was achieved, up to 3 STIs were undertaken. Two ARV cycles were allowed after each interruption if virologic rebound to more than 5000 RNA copies/mL occurred. Treatment success was defined as maintaining viral loads below 5000 copies/mL for 6 months after ARV interruption. RESULTS: Sixty-eight male homosexual patients were randomized: 35 to ARV + HU and 33 to ARV-alone. Median baseline HIV RNA was 5.73 log10 copies/mL, and median CD4 T-lymphocyte count was 517 cells/microL. Treatment success was not significantly different between those receiving and not receiving HU, with 9 (26%) and 9 (27%), respectively, maintaining viral load at less than 5000 copies/mL in each group (P = 0.88). Virologic control was achieved by 11 (19%) of 59 after 1 STI, 1 (2%) of 41 after 2 STIs, and 6 (17%) of 36 after the third STI. Serious adverse events were recorded for 9 (26%) of 35 of patients using HU and 3 (9%) of 33 in the ARV-only group (P = 0.28). CD4 cell increases were significantly blunted for the HU group compared to the ARV-alone group after the initial treatment phase (+101 cells vs. +196 cells, respectively, P = 0.006). CONCLUSIONS: Hydroxyurea was not found to be beneficial when used in association with STIs in patients during PHI.     

Highly active antiretroviral therapy interruption: predictors and virological and immunologic consequences

OBJECTIVE: To characterize the magnitude and the predictors of highly active antiretroviral therapy (HAART) interruption (TI) and to investigate its immunologic and virological consequences. METHODS: Using Concerted Action on Seroconversion to AIDS and Death in Europe data from 8,300 persons with well-documented seroconversion dates, we identified subjects with stable first HAART (for at least 90 days) not initiated during primary infection. A TI was defined as an interruption of all antiretroviral therapy drugs for at least 14 days. RESULTS: Of 1,551 subjects starting HAART, 299 (19.3%) interrupted treatment. Median (interquartile range) duration of the TI was 189 (101-382) days. The cumulative probability (95% confidence interval) of TI at 2 years was 15.9% (14.0%-18.1%). Women were more likely to have a TI than men in the same exposure group (35.8% vs 24.2% among drug users, 22.1% vs 13.3% among heterosexuals; P < 0.05). Higher baseline viremia and poor immunologic response to HAART were associated with higher probabilities of TI. Median (interquartile range) individual CD4 cell loss during TI was 94 (1-220) cells/microL. Older age at HAART (>40 yr), lower pre-HAART nadir (<200 cells/microL), and lower CD4 at start of TI (<350 cells/microL) were significantly associated with greater relative CD4 loss during TI. CONCLUSIONS: We estimate that almost 1 in 6 subjects on HAART interrupts treatment by 2 years. Further research is needed to investigate the reasons why TI is higher in women. We have identified characteristics of subjects with the greatest risk for CD4 loss in whom TI may have greater risks.     

Lopinavir/ritonavir as single-drug therapy for maintenance of HIV-1 viral suppression: 48-week results of a randomized, controlled, open-label, proof-of-concept pilot clinical trial (OK Study)

OBJECTIVE: This study evaluated maintenance with lopinavir/ritonavir monotherapy vs. continuing lopinavir/ritonavir and 2 nucleosides in HIV-infected patients with suppressed HIV replication. DESIGN: Randomized, controlled, open-label, multicenter, pilot clinical trial. METHODS: Adult patients were eligible if they had no history of virologic failure while receiving a protease inhibitor, were receiving 2 nucleosides + lopinavir/ritonavir (400/100 mg b.i.d.) for >1 month and had maintained serum HIV RNA <50 copies/mL for >6 months prior to enrollment. RESULTS: Forty-two patients were randomly assigned 1:1 to continue or stop the nucleosides. At baseline there were no significant differences between groups in median CD4 cells/muL (baseline or nadir), pre-HAART (highly active antiretroviral therapy) HIV log10 viremia, or time with HIV RNA <50 copies/mL prior to enrollment. After 48 weeks of follow-up, percentage of patients remaining at <50 HIV RNA copies/mL (intention to treat, M = F) was 81% for the monotherapy group (95% CI: 64% to 98%) vs. 95% for the triple-therapy group (95% CI: 86% to 100%); P = 0.34. Patients in whom monotherapy failed had significantly worse adherence than patients who remained virally suppressed on monotherapy. Monotherapy failures did not show primary resistance mutations in the protease gene and were successfully reinduced with prerandomization nucleosides. Mean change in CD4 cells/microL: +70 (monotherapy) and +8 (triple) (P = 0.27). Mean serum fasting lipids remained stable in both groups. No serious adverse events were observed. CONCLUSION: Most of the patients maintained with lopinavir/ritonavir monotherapy remain with undetectable viral load after 48 weeks. Failures of lopinavir/ritonavir monotherapy were not associated with the development of primary resistance mutations in the protease gene and could be successfully reinduced adding back prior nucleosides.     

Meta-analysis of two randomized controlled trials comparing combined zidovudine and didanosine therapy with combined zidovudine, didanosine, and nevirapine therapy in patients with HIV. INCAS study team

OBJECTIVES: To extend the range of CD4 counts in which a plasma viral load nadir (pVL) <20 copies/ml was known to be predictive of the duration of virologic response. To determine whether baseline pVL is predictive of virologic response during the study periods. METHODS: A meta-analysis was conducted of the original individual patient data from two randomized controlled trials comparing zidovudine (ZDV)/didanosine (ddI) with ZDV/ddI/nevirapine (NVP). RESULTS: In total, 87 patients received ZDV/ddI and 83 received ZDV/ddI/NVP. Study subjects on triple therapy with baseline pVL <100,000 copies/ml were more likely to achieve a pVL <400 copies/ml (odds ratio [OR] = 2.49; p = .02) and <20 copies/ml (OR = 4.76; p = .001) during the trial than those with baseline pVL > 100,000 copies/ml. Among triple therapy patients, the relative risk of virologic failure was higher for patients with higher baseline pVL (rate ratio [RR] = 2.51/log10 copies/ ml; p = .01), after controlling for compliance and pVL nadir. The relative risks of virologic failure associated with pVL nadir <20 copies/ml and between 21 and 400 copies/ml were .04 (p = .0001) and .56 (p = .26), respectively, compared with patients with a pVL nadir >400 copies/ml. CONCLUSIONS: We have extended our earlier results that achieving a pVL nadir <20 copies/ml is important for maintaining virologic suppression. In particular, we have demonstrated that a pVL nadir <20 copies/ml is at least fivefold more protective against virologic failure than achieving a pVL nadir between 20 and 400 copies/ml. Baseline pVL is significantly associated with the probability of achieving and sustaining virologic suppression.     

CD4 decline and incidence of opportunistic infections in Cape Town, South Africa: implications for prophylaxis and treatment

OBJECTIVES: To determine the rate of CD4 decline and the incidence of opportunistic infections (OIs) among antiretroviral therapy-naive South African HIV-infected patients and inform timing of OI prophylaxis. METHODS: We used mixed-effect models to estimate CD4 cell decline by CD4 cell count strata in HIV-infected patients in the Cape Town AIDS Cohort between 1984 and 2000. Stratum-specific OI incidence per 100 person-years of observation was determined using incidence density analysis. RESULTS: Nine hundred seventy-four patients with 2 or more CD4 cell counts were included. CD4 counts declined by 47.1 cells/microL per year in the stratum with more than 500 cells/microL stratum, 30.6 cells/microL per year in the stratum with 351 to 500 cells/microL, and 20.5 cells/microL per year in the stratum with 201 to 350 cells/microL. Tuberculosis and oral candidiasis were the only OIs that occurred frequently in the stratum with more than 200 CD4 cells/microL. Rates of chronic diarrhea, wasting syndrome, tuberculosis, and oral and esophageal candidiasis increased in the stratum with less than 200 cells/microL, and rates of all OIs were highest in the stratum with 50 cells/microL or less. CONCLUSIONS:: CD4 cell count declines were dependent on CD4 strata and can inform timing of clinic visits and treatment initiation in South Africa. Incidence rates of OIs suggest that targeted OI prophylaxis could prevent substantial HIV-related morbidity in South Africa.