Browsing by Author "Cois, Annibale"

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    Analysing the socioeconomic determinants of hypertension in South Africa: a structural equation modelling approach
    (BioMed Central, 2014-05-01) Cois, Annibale; Ehrlich, Rodney
    Abstract Background Epidemiological research has long observed a varying prevalence of hypertension across socioeconomic strata. However, patterns of association and underlying causal mechanisms are poorly understood in sub-Saharan Africa. Using education and income as indicators, we investigated the extent to which socioeconomic status is linked to blood pressure in the first wave of the National Income Dynamics Study — a South African longitudinal study of more than 15000 adults – and whether bio-behavioural risk factors mediate the association. Methods In a cross-sectional analysis, structural equation modelling was employed to estimate the effect of socioeconomic status on systolic and diastolic blood pressure and to assess the role of a set of bio-behavioural risk factors in explaining the observed relationships. Results After adjustment for age, race and antihypertensive treatment, higher education and income were independently associated with higher diastolic blood pressure in men. In women higher education predicted lower values of both diastolic and systolic blood pressure while higher income predicted lower systolic blood pressure. In both genders, body mass index was a strong mediator of an adverse indirect effect of socioeconomic status on blood pressure. Together with physical exercise, alcohol use, smoking and resting heart rate, body mass index therefore contributed substantially to mediation of the observed relationships in men. By contrast, in women unmeasured factors played a greater role. Conclusion In countries undergoing epidemiological transition, effects of socioeconomic status on blood pressure may vary by gender. In women, factors other than those listed above may have substantial role in mediating the association and merit investigation.
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    Analysing the socioeconomic determinants of hypertension in South Africa: A structural equation modelling approach
    (2012) Cois, Annibale; Ehrlich, Rodney
    Epidemiological research has long since observed that the prevalence of hypertension varies across populations' socioeconomic strata. Higher socioeconomic status (SES) has been consistently associated with lower levels of blood pressure in most studies from Europe and North America, while research in low- and middle-income countries at an earlier stage of the epidemiological transition revealed mixed patterns. The causal mechanisms underlying these varying relationships are largely unknown. Only in recent years the pathways through which SES impacts the cardiovascular system have been explored in large-scale studies, with results suggesting that body mass index, heart rate, and to a lesser extent physical exercise, alcohol use and smoking, may play a role in mediating these associations. However, these results refer to high-income countries, while similar research in low- and middle-income countries, and sub-Saharan Africa in particular, is lacking. In 2008, the National Income Dynamics Study (NIDS) collected a broad range of information on a representative sample of the population of South Africa, a medium-income country undergoing rapid epidemiological transition. Among other topics, information was gathered on blood pressure, biologic and behavioural risk factors, education, income and other indicators of socioeconomic position.
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    Obesity trends and risk factors in the South African adult population
    (BioMed Central, 2015-10-13) Cois, Annibale; Day, Candy
    Background: Obesity prevalence is increasing globally and contributes substantially to the burgeoning burden of non-communicable diseases. South Africa is particularly affected by this increasing trend and cross-sectional evidence suggests socioeconomic and behavioural variables as possible drivers. However, no large scale longitudinal study has attempted the direct identification of risk factors for progression towards obesity. Methods: This study analysed data on 10,100 South African adults (18 years and over) randomly selected in 2008 and successfully recontacted in 2010 and 2012. Latent Growth Modelling was used to estimate the average rate of change in body mass index (BMI) during the study period, and to identify baseline characteristics associated with different trajectories. Results: The overall rate of change in BMI during the study period was +1.57 kg/m2 per decade (95 % CI: 0.93−2.22), and it was higher among women (+1.82 kg/m2 per decade, 95 % CI: 1.06−2.58) than among men (+1.03 kg/m2 per decade; 95 % CI: 0.14−1.93). Female gender, younger age, larger waist circumference, white population group and higher household income per capita were baseline characteristics associated with higher rates of change. The association between tobacco use and obesity was complex. Smoking was associated with greater waist circumference at baseline but lower rates of increase in BMI during the study period. Quitting smoking was an independent predictor of BMI increase among subjects with normal weight at baseline. Among subjects with baseline BMI lower than 25 kg/m2, rates of changes were higher in rural than urban areas, and inversely related to the frequency of physical exercise. Conclusions: A strong positive trend in BMI remains in South Africa and obesity prevalence is likely to increase. Trends are not homogeneous, and high risk groups (subjects with high socioeconomic status, rural dwellers, young women) and modifiable risk factors (physical inactivity) can be targeted. Subjects quitting smoking should receive additional weight-loss support in order that the numerous health benefits of cessation are not reduced by increasing BMI. Centrally obese subjects should be targeted in campaigns.
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    Predictors of silicosis and variation in prevalence across mines among employed gold miners in South Africa
    (2020-06-01) Knight, Dave; Ehrlich, Rodney; Cois, Annibale; Fielding, Katherine; Grant, Alison D; Churchyard, Gavin
    Background The stated intention to eliminate silicosis from the South African goldmining industry as well as current programmes to find and compensate ex-miners with silicosis require an understanding of variation in silicosis prevalence across the industry. We aimed to identify the predictors of radiological silicosis in a large sample of working miners across gold mines in South Africa. Methods Routine surveillance chest radiographs were collected from 15 goldmine “clusters” in a baseline survey undertaken in preparation for a separate tuberculosis isoniazid prophylaxis trial. All images were read for silicosis by a health professional experienced in using the International Labour Organisation (ILO) classification. Profusion thresholds of > 1/0 and > 1/1 were used. Demographic and occupational information was obtained by questionnaire. Predictors of silicosis were examined in a multivariable logistic regression model, including age, gender, racial ascription, country of origin, years since starting mine employment, mine shaft, skill category, underground work status and tuberculosis. Results The crude silicosis prevalence at ILO > 1/1 was 3.8% [95% confidence interval (CI) 3.5–4.1%]. The range across mine shafts was 0.8–6.9%. After adjustment for covariates, the interquartile range across shafts was reduced from 2.4 to 1.2%. Black miners [adjusted odds ratio (aOR) 2.8; 95% CI 1.1–7.2] and miners in full-time underground work (aOR 2.1; 95% CI 1.3–3.4) had substantially elevated odds of silicosis, while workers from Mozambique had lower odds (aOR 0.54; 95% CI 0.38–0.77). Silicosis odds rose sharply with both age and years since starting in the industry (p for linear trend < 0.005), with 95.5% of affected miners having > 15 years since first exposure and 2.2% < 10 years. Conclusions In surveillance of silicosis in working gold miners time since first exposure remains a powerful predictor. Age appears to be an independent predictor, while the detection of radiological silicosis in short-service miners requires attention. Public risk reporting by mines should include factors bearing on silicosis prevalence, specifically dust concentrations, with independent verification. Studies of silicosis and tuberculosis in ex-miners are needed, supported by an accessible electronic database of the relevant medical and dust exposure records of all gold miners.
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    Problem drinking as a risk factor for tuberculosis: a propensity score matched analysis of a national survey
    (BioMed Central Ltd, 2013) Cois, Annibale; Ehrlich, Rodney
    BACKGROUND:Epidemiological and other evidence strongly supports the hypothesis that problem drinking is causally related to the incidence of active tuberculosis and the worsening of the disease course. The presence of a large number of potential confounders, however, complicates the assessment of the actual size of this causal effect, leaving room for a substantial amount of bias. This study aims to contribute to the understanding of the role of confounding in the observed association between problem drinking and tuberculosis, assessing the effect of the adjustment for a relatively large number of potential confounders on the estimated prevalence odds ratio of tuberculosis among problem drinkers vs. moderate drinkers/abstainers in a cross-sectional, nationally representative sample of the South African adult population. METHODS: A propensity score approach was used to match each problem drinker in the sample with a subset of moderate drinkers/abstainers with similar characteristics in respect to a set of potential confounders. The prevalence odds ratio of tuberculosis between the matched groups was then calculated using conditional logistic regression. Sensitivity analyses were conducted to assess the robustness of the results in respect to misspecification of the model. RESULTS: The prevalence odds ratio of tuberculosis between problem drinkers and moderate drinkers/abstainers was 1.97 (95% CI: 1.40 to 2.77), and the result was robust with respect to the matching procedure as well as to incorrect adjustment for potential mediators and to the possible presence of unmeasured confounders. Sub-population analysis did not provide noteworthy evidence for the presence of interaction between problem drinking and the observed confounders. CONCLUSION: In a cross-sectional national survey of the adult population of a middle income country with high tuberculosis burden, problem drinking was associated with a two fold increase in the odds of past TB diagnosis after controlling for a large number of socio-economic and biological confounders. Within the limitations of a cross-sectional study design with self-reported tuberculosis status, these results adds to previous evidence of a causal link between problem drinking and tuberculosis, and suggest that the observed higher prevalence of tuberculosis among problem drinkers commonly found in population studies cannot be attributed to the confounding effect of the uneven distribution of other risk factors.
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    Self-reported side effects and adherence to antiretroviral therapy in HIV-infected pregnant women under option B+: a prospective study
    (Public Library of Science, 2016) Phillips, Tamsin; Cois, Annibale; Remien, Robert H; Mellins, Claude A; McIntyre, James A; Petro, Greg; Abrams, Elaine J; Myer, Landon
    BACKGROUND: Antiretroviral therapy (ART) regimens containing efavirenz (EFV) are recommended as part of universal ART for pregnant and breastfeeding women. EFV may have appreciable side effects (SE), and ART adherence in pregnancy is a major concern, but little is known about ART SE and associations with adherence in pregnancy. METHODS: We investigated the distribution of patient-reported SE (based on Division of AIDS categories) and the association of SE with missed ART doses in a cohort of 517 women starting EFV+3TC/FTC+TDF during pregnancy. In analysis, SE were considered in terms of their overall frequency, by systems category, and by latent classes. RESULTS: Overall 97% of women reported experiencing at least one SE after ART initiation, with 48% experiencing more than five SE. Gastrointestinal, central nervous system, systemic and skin SE were reported by 81%, 85%, 79% and 31% of women, respectively, with considerable overlap across groups. At least one missed dose was reported by 32% of women. In multivariable models, ART non-adherence was associated with systemic SE compared to other systems categories, and measures of the overall burden of SE experienced were most strongly associated with missed ART doses. CONCLUSION: These data demonstrate very high levels of SE in pregnant women initiating EFV-based ART and a strong association between SE burden and ART adherence. ART regimens with reduced SE profiles may enhance adherence, and as countries expand universal ART for all adult patients, counseling must include preparation for ART SE.
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    Understanding blood pressure dynamics in the South African population: a latent variables approach to the analysis and comparison of data from multiple surveys
    (2017) Cois, Annibale; Ehrlich, Rodney I; Er, Şebnem
    Background: The 2015 edition of the Global Burden of Diseases Study identified elevated systolic blood pressure─ defined as systolic blood pressure greater than the minimum risk category of 110–115 mm Hg ─ as the largest single contributor to the global burden of disease, responsible for 211.8 million disability adjusted life years lost, up 8.8% in the last decade. Middle‐income countries are currently bearing the highest share of this burden, and, because of the rapid demographic transition towards larger and older populations, the burden is bound to increase rapidly in the coming years, unless age‐specific values of blood pressure are substantially reduced to compensate for the unfavourable demographic changes. Achieving this more favourable blood pressure distribution in populations undergoing rapid changes in their socioeconomic structure requires knowledge of the mechanisms underlying temporal variations of blood pressure and the relationships of such variations with socioeconomic variables.However, evidence on these mechanisms and reliable information on the temporal trends of blood pressure themselves are scant outside high‐income countries. Given the large gain in health that would result in low‐ and middle‐income countries if an optimal blood pressure were to be achieved in large sectors of the population, there is little doubt that temporal trends in the distribution of blood pressure in these populations and their possible determinants are an open and important area for investigation. Objectives: Objectives of the study were: 1. To assess the level of quality and comparability of blood pressure data collected in a series of large‐scale surveys carried out between 1998 and 2015 in South Africa, a middle‐income country undergoing rapid demographic and epidemiological transition; 2. To explore the possibility of applying a series of latent variables techniques to improve the comparability of data from the different sources and to minimise the effect of measurement and representation error on the estimation of cross‐sectional relationships and temporal trends; 3. To estimate changes in the distribution of blood pressure and derived quantities ‐‐‐ such as prevalence of uncontrolled hypertension ‐‐‐ in the South African adult population between 1998 and 2015, taking into account between‐surveys differences and measurement and representation error that could lead to artefactual conclusions; 4. To estimate the extent to which the estimated changes in the blood pressure distribution during the study period could be explained by concurrent changes in the distribution of a series of biological, behavioural and socioeconomic risk factors. Methods: A series of techniques within the general framework of structural equation modelling were applied to jointly analyse the data and estimate the temporal trends and relationships of interest. Results: The average systolic and diastolic blood pressure of South African adult women has progressively decreased since 2003‐2004, reversing the previous rising trend. Among men, the reversal happened only for the systolic blood pressure, while the average diastolic blood pressure continued rising, although at a lower pace than previously.In both genders, this pattern resulted in a reduction of the prevalence of uncontrolled hypertension between 2003‐2004 and 2014‐2015, by 8 percentage points among women and by 4.5 percentage points among men. This consistent and rapid decrease cannot be explained by changes in the age structure of the population, smoking and alcohol consumption habits, distribution of body mass index or urbanization. The diffusion of antihypertensive treatment and, among women, cohort effects and rapidly increasing educational level partly explain the recent trend, but a substantial part of the observed decrease remains unexplained by the factors available in our analyses. Large seasonal variations in both systolic and diastolic blood pressure are present in the South African population, and their magnitude is greater among population strata with low socioeconomic status. From a methodological point of view, there were two further results of this study. First, estimates of blood pressure and related quantities from the eight large‐scale population surveys carried out in South Africa between 1998 and 2015are not directly comparable, because of methodological differences and overall data quality. Second, structural equation modelling (and, within this general framework, multiple group modelling, normal‐censored regression, mixture analysis with skew‐normal distributions and the use of additional parameters and phantom variables) represent a viable and advantageous alternative to current methods of comparative analysis of blood pressure data. Conclusions: Encouraging signs regarding the future development of the burden of diseases related to elevated blood pressure in the South African population emerge from this study. Age‐specific prevalence of uncontrolled hypertension seems to be decreasing, especially among women, and this decrease is accompanied by declining mortality for cardiovascular disease, particularly for stroke, recorded in burden of mortality studies. The reasons of this decrease are largely unexplained and warrant further investigation. However, among the possible drivers analysed in this study, increased accessibility and efficacy of antihypertensive treatment are likely to be playing a role in the observed decrease in blood pressure. The growing obesity epidemic, on the contrary, is likely to be limiting the achievable benefits. Both of these factors can be targeted to maintain and improve the current decline in population values of blood pressure and prevalence of hypertension. The large seasonal variations of blood pressure and their unequal distribution across socioeconomic strata also suggest that interventions to reduce exposure to low temperatures might have public health benefit. From the point of view of the epidemiological investigation, the results of this study suggest that the current methods for the analysis of survey data on blood pressure and the measurement protocols for future data collections should be improved to increase between‐surveys comparabilityand gather more reliable information on temporal changes in BP and gain better understanding of their drivers. Specifically, analytical methods should take explicitly into account known sources of measurement and representation error to reduce their biasing effects, especially when inter‐survey comparisons are involved. Protocols for future studies should routinely include collection of auxiliary information and/or explicit validation of devices and procedures in the specific population.