Browsing by Subject "Linear regression analysis"

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    Antiretroviral therapy, especially Efavirenz, is associated with low bone mineral density in HIV-infected South Africans
    (Public Library of Science, 2015) Dave, Joel A; Cohen, Karen; Micklesfield, Lisa K; Maartens, Gary; Levitt, Naomi S
    Purpose We determined the prevalence and correlates of low bone mineral density (BMD) in HIV-infected South Africans as there is a paucity of such data from Africa. METHODS: BMD and serum 25-hydroxyvitamin D were measured in HIV-positive participants on antiretroviral therapy (ART) and in those not yet on ART (ART-naïve). RESULTS: We enrolled 444 participants [median age 35(IQR: 30, 40) years; 77% women]. BMD was low (z score <-2SD) in 17% and 5% of participants at the lumbar spine and total hip, respectively. Total hip [0.909 (SD 0.123) vs 0.956 (SD 0.124) g/cm 2 , p = 0.0001] and neck of femur BMD [0.796 (SD 0.130) vs 0.844 (SD 0.120) g/cm 2 , p = 0.0001] were lower in the ART, compared to the ART-naïve group. Vitamin D deficiency was present in 15% of participants and was associated with efavirenz use [adjusted OR 2.04 (95% CI 1.01 to 4.13)]. In a multivariate linear regression, exposure to efavirenz or lopinavir-based ART was associated with lower total hip BMD, whereas higher weight, being male and higher vitamin D concentration were associated with higher total hip BMD (adjusted R 2 = 0.28). Age, weight, sex, and the use of efavirenz-based ART were independently associated with lumbar spine BMD (adjusted R 2 = 0.13). CONCLUSIONS: Vitamin D status, use of efavirenz or lopinavir/ritonavir, weight, age and sex are significantly associated with lower BMD in this young cohort of HIV-infected South Africans.
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    Differing patterns of overweight and obesity among black men and women in Cape Town: the CRIBSA study
    (Public Library of Science, 2014) Peer, Nasheeta; Lombard, Carl; Steyn, Krisela; Gwebushe, Nomonde; Levitt, Naomi
    Objectives To ascertain the prevalence and determinants of overweight/obesity in the 25-74-year-old urban black population of Cape Town and examine the changes between 1990 and 2008/09. METHODS: In 2008/09, a representative cross-sectional sample, stratified for age and sex, was randomly selected from the same townships sampled in 1990. Data were collected by questionnaires, clinical measurements and biochemical analyses. Gender-specific linear regression models evaluated the associations with overweight/obesity. RESULTS: There were 1099 participants, 392 men and 707 women (response rate 86%) in 2008/09. Mean body mass index (BMI) and waist circumference (WC) were 23.7 kg/m 2 (95% confidence interval (CI): 23.1-24.2) and 84.2 cm (95% CI: 82.8-85.6) in men, and 33.0 kg/m 2 (95% CI: 32.3-33.7) and 96.8 cm (95% CI: 95.5-98.1) in women. Prevalence of BMI ≥25 kg/m 2 and raised WC were 28.9% (95% CI: 24.1-34.3) and 20.1% (95% CI: 15.9-24.9) in men, and 82.8% (95% CI: 79.3-85.9) and 86.0% (95% CI: 82.9-88.6) in women. Among 25-64-year-olds, BMI ≥25 kg/m 2 decreased between 1990 (37.3%, 95% CI: 31.7-43.1) and 2008/09 (27.7%, 95% CI: 22.7-33.4) in men but increased from 72.7% (95% CI: 67.6-77.2) to 82.6% (95% CI: 78.8-85.8) in women. In the regression models for men and women, higher BMI was directly associated with increasing age, wealth, hypertension and diabetes but inversely related to daily smoking. Also significantly associated with rising BMI were raised low-density lipoprotein cholesterol and being employed compared to unemployed in men, and having >7 years of education in women. CONCLUSIONS: Overweight/obesity, particularly in urban black women, requires urgent action because of the associations with cardiovascular disease risk factors and their serious consequences.
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    Growth of HIV-exposed uninfected infants in the first 6 months of life in South Africa: The IeDEA-SA collaboration
    (Public Library of Science, 2016) Morden, Erna; Technau, Karl-Günter; Giddy, Janet; Maxwell, Nicola; Keiser, Olivia; Davies, Mary-Ann
    BACKGROUND: HIV-exposed uninfected (HEU) infants are a growing population in sub-Saharan Africa especially with the increasing coverage of more effective prevention of mother-to-child transmission (PMTCT) antiretroviral therapy regimens. This study describes the characteristics of South African HEU infants, investigates factors impacting birth weight and assesses their growth within the first 28 weeks of life. METHODS: This is a retrospective cohort based on routine clinical data from two South African PMTCT programmes. Data were collected between 2007 and 2013. Linear regression assessed factors affecting birth weight-for-age z-scores (WAZ) while growth (longitudinal WAZ) was assessed using mixed effects models. RESULTS: We assessed the growth of 2621 HEU infants (median birth WAZ was -0.65 (IQR -1.46; 0.0) and 51% were male). The feeding modalities practised were as follows: 0.5% exclusive breastfeeding, 7.9% breastfeeding with unknown exclusivity, 0.08% mixed breastfeeding and 89.2% formula feeding. Mothers with CD4 <200 cells/μl delivered infants with a lower birth WAZ (adjusted ß -0.253 [95% CI -0.043; -0.072], p = 0.006) compared to mothers with aCD4 ≥500 cells/μl. Similarly, mothers who did not receive antiretroviral drugs delivered infants with a lower birth WAZ (adjusted ß -0.39 [95% CI -0.67; -0.11], p = 0.007) compared to mothers who received antenatal antiretrovirals. Infants with a birth weight <2 500g (ß 0.070 [95% CI 0.061; 0.078], p <0.0001) experienced faster growth within the first 28 weeks of life compared to infants with a birth weight ≥2 500g. Infants with any breastfeeding exposure experienced slower longitudinal growth compared to formula fed infants (adjusted ß -0.012 [95% CI 0.021; -0.003], p = 0.011). CONCLUSION: Less severe maternal disease and the use of antiretrovirals positively impacts birth weight in this cohort of South African HEU infants. Formula feeding was common with breastfed infants experiencing marginally slower longitudinal growth.
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    Recreational fish-finders - an inexpensive alternative to scientific echo-sounders for unravelling the links between marine top predators and their prey
    (Public Library of Science, 2015) McInnes, Alistair M; Khoosal, Arjun; Murrell, Ben; Merkle, Dagmar; Lacerda, Miguel; Nyengera, Reason; Coetzee, Janet C; Edwards, Loyd C; Ryan, Peter G; Rademan, Johan
    Studies investigating how mobile marine predators respond to their prey are limited due to the challenging nature of the environment. While marine top predators are increasingly easy to study thanks to developments in bio-logging technology, typically there is scant information on the distribution and abundance of their prey, largely due to the specialised nature of acquiring this information. We explore the potential of using single-beam recreational fish-finders (RFF) to quantify relative forage fish abundance and draw inferences of the prey distribution at a fine spatial scale. We compared fish school characteristics as inferred from the RFF with that of a calibrated scientific split-beam echo-sounder (SES) by simultaneously operating both systems from the same vessel in Algoa Bay, South Africa. Customized open-source software was developed to extract fish school information from the echo returns of the RFF. For schools insonified by both systems, there was close correspondence between estimates of mean school depth (R 2 = 0.98) and school area (R 2 = 0.70). Estimates of relative school density (mean volume backscattering strength; S v ) measured by the RFF were negatively biased through saturation of this system given its smaller dynamic range. A correction factor applied to the RFF-derived density estimates improved the comparability between the two systems. Relative abundance estimates using all schools from both systems were congruent at scales from 0.5 km to 18 km with a strong positive linear trend in model fit estimates with increasing scale. Although absolute estimates of fish abundance cannot be derived from these systems, they are effective at describing prey school characteristics and have good potential for mapping forage fish distribution and relative abundance. Using such relatively inexpensive systems could greatly enhance our understanding of predator-prey interactions.