More adult patients aged less than 50 years were female (66 vs. 51%; P < 0.001), had a diagnosis of TB at ART initiation (8 vs. 6%; P < 0.001), and were treated in an urban clinic setting (45 vs. 40%; P < 0.001) than patients aged at least 50 years (Table 1). Patients in both age groups were recorded as having similar rates of severe immunosuppression (38 vs. 37%; P = 0.14).
Immune restoration, mortality and loss to follow-up
Patients were followed for an average of 1 year (IQR 0.34–1.92 years) with patients aged less than 50 followed for slightly less time than those at least 50 years (1.00 vs. 1.08 years, P = 0.007). The crude mortality rate for patients aged at least 50 years was significantly higher than for those aged less than 50 years [rate ratio (RR) 1.22, 95% confidence interval (CI) 1.03–1.43, P = 0.016], whereas the rate of loss to follow-up was not significantly different (RR 1.07, 95% CI 0.96–1.18, P = 0.19). The median gain in CD4 cell count at 6 and 12 months was significantly higher in patients less than 50 years old compared with those at least 50 years (134 vs. 112 at 6 months; 170 vs. 139 at 12 months; both P < 0.001). Only 28 and 21% of patients overall (similar by age group) had CD4 cell count measurements at both baseline and 6 or 12 months, respectively, and although most variables differed between those who did and did not have CD4 cell count measurements, there was no significant difference in median age (results not shown).
Cox proportional hazards analysis found that all patients aged at least 40 years were at increased mortality risk from more than 3 to 42 months on ART after adjusting for sex, current TB, BMI, severe immunosuppression and clinic setting [40–49 years: adjusted hazard ratio (aHR) 1.59, 95% CI 1.29–1.96, P < 0.001; 50–59 years: aHR 1.58, 95% CI 1.19–2.11, P = 0.002; 60–69 years: aHR 2.63, 95% CI 1.66–4.16, P < 0.001; 70–94 years: aHR 3.64, 95% CI 1.51–8.77, P = 0.004; Table 3; Fig. 1a]. In addition, there was a significantly increased risk of mortality in those aged 70–94 years compared with patients aged 15–39 years during the first 3 months on ART (aHR 3.18, 95% CI 2.12–4.77; P < 0.001). Severe immunosuppression at ART initiation was most strongly associated with mortality (>0–3 months follow-up: aHR 2.19, 95% CI 1.83–2.63, P = 0.008; >3–42 months follow-up: aHR 1.83, 95% CI 1.52–2.21, P < 0.001), and each unit increase in BMI reduced risk of mortality (aHR 0.88 and 0.91 for >0–3 months and >3–42 months follow-up, respectively, P < 0.001). Rural clinic setting was protective against mortality in the first 3 months of ART (aHR 0.80, 95% CI 0.68–0.95, P = 0.009) but a risk thereafter (aHR 1.27, 95% CI 1.05–1.52, P = 0.013). Conversely, increasing age was not associated with risk of loss to follow-up in any of the periods of follow-up assessed after adjusting for sex, current TB, BMI, severe immunosuppression and clinic setting (Table 4; Fig. 1b). The most significant factor associated with loss to follow-up was the clinic being in a rural setting, with risk increasing with greater follow-up time (Table 4).
The association between increasing age and mortality in the adjusted model was robust to leaving out any single country (Table 2), and a regression that assessed the potential for loss to follow-up as a competing risk (subhazard ratio 1.15, 95% CI 1.08–1.21).
All of the models displayed proportional hazards except for loss to follow-up up until 12 months on ART (Schoenfeld residual P = 0.002, Table 4), primarily because of the BMI variable, even after applying a range of statistical contingencies to attempt to obtain proportionality, including categorization, transformation, removal of data outliers and assessment of possible interactions.
HIV/AIDS has resulted in a dramatic decline in life expectancy in sub-Saharan Africa,  but with ART, people living with HIV/AIDS can enjoy almost normal life expectancy . The neglect of older age groups in the HIV/AIDS response in sub-Saharan Africa is partly due to a perception that populations in the most affected countries are unlikely to achieve old age anyway and so a focus on younger patients represents a more reasonable public health approach. However, our study shows that older age groups represent an important proportion of the overall ART population. More than one in 10 people on ART in this study were found to be aged 50 years or over, a proportion consistent across most of the nine sub-Saharan Africa countries under review.
Previous studies have reported that people aged 50 or over were at higher risk of mortality compared with younger adults [5–7]. In this study, we found that mortality risk increased as age increased after 3 months on ART, suggesting that a simple age cut-off may not be sufficient for defining older groups at heightened risk of death.
In developed countries, the increased risk of death among HIV patients in older age groups is explained by the increased risk of development of non-AIDS-defining illnesses such as cardiovascular and liver disease, renal impairment and malignancies . A recent study from Botswana found increased risk of non-AIDS-defining illnesses among higher age groups, with standardized rates higher than reported in the United States . Although this is likely to explain some of the excess mortality observed in our cohorts, it is important to note that older age groups are also at greater risk of infectious diseases, particularly TB, as a result of declines in immunity associated with older age .
The reason for higher mortality among older people with HIV/AIDS is multifactorial, with the natural aging process, immune senescence, antiretroviral drug toxicities and HIV infection all suggested to play a role [18,19]. We found that patients aged at least 50 years had a significantly lower CD4 gain at 6 and 12 months on ART, a finding consistent with those from a large observational cohort study from 33 European cohorts which found that the probability of immunological response reduced in those aged 60 years or older . This gives further cause for concern about potential vulnerability to incident opportunistic infections and suggests a need for rapid ART initiation as soon as clinically eligible.
Our results are based on data pooled from different programmes in which HIV care was provided both as a disease-specific programme and integrated into general healthcare, in urban and rural areas and across a number of countries. This allows some confidence in the generalizability of our findings to other programmes in sub-Saharan Africa. Leaving out any single country did not importantly influence the role of age on mortality. We were able to control for a number of patient and programme-level variables, but cannot exclude the possibility of residual confounding. Despite various attempts to obtain proportionality, one of the Cox hazards models did not adhere to the assumption of proportional hazards; however, BMI was retained in the model as a clinically important factor related to poor outcomes. The likely effect of a nonproportional predictor is that the power of the test for this variable is reduced, such that any association may be missed, and the concurrent model predictors that do satisfy proportionality also suffer from decreased power associated with a poorer overall model fit . Finally, we were unable to report on a number of important variables due to the limits of routine programme reporting. In common with reports from other routine programmes in sub-Saharan Africa , CD4 cell counts were not available for a substantial number of patients. Thus, we are unable to report on the association between excess mortality and age-related decline in immune status; nevertheless, higher mortality at older age groups was still seen after controlling for a composite measure of immunosuppression combining CD4 cell count and WHO stage. Specific causes of death could also not be reported because this was not routinely reported and links to death registries were not established in these settings. We could not assess association of HIV status and expected risk of mortality with age in these settings, as data was from routine monitoring of dedicated HIV programmes.
In conclusion, this study provides further evidence that older age groups are a vulnerable group in ART programmes and suggests that, although it is important to identify groups in need of more careful follow-up and earlier initiation on ART, the application of crude age categories may result in patients at higher risk being overlooked. Future research is now needed to understand the reasons for higher mortality in older age groups, and defining simple interventions that are feasible in highly under-resourced settings to allow for adapted follow-up and care approaches for older age groups.
The authors would like to thank Leslie Shanks for encouraging comments on an earlier draft.
Conflicts of interest
There are no conflicts of interest.
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Keywords:© 2012 Lippincott Williams & Wilkins, Inc.
antiretroviral therapy; elderly; HIV/AIDS; older adults; survival