The effect of peer and parental smoking on adolescent smoking initiation: Exploring potential moderators

The factors that contribute to smoking initiation among adolescents are poorly understood. The current approaches to smoking prevention may have achieved their maximum potential as evidenced by a stalling in the decline in smoking rates. To date, approaches to smoking prevention based on social and individual factors have previously met with limited success. A promising new approach will be to examine the interaction between social and individual factors and the effects of their interaction on smoking initiation. Parental and peer smoking behaviors are well-known risk factors for smoking initiation. Several theoretical models suggest that perceptual or interpretative processes may moderate the influence of factors such as these on the smoking initiation process. This study looks at age (as a proxy for adolescent development), depression and school performance as potential moderators of the impact of parental or peer smoking. This study uses a large longitudinal sample (The Teenage Attitudes and Practices Surveys -- 1989 and 1993) to explore for these relationships. Results show very limited support for the impact of potential moderated relationships, with only one of the six hypothesized interactions being supported (peer smoking and school performance). This would suggest that theoretical models which include concepts of perceptual or interpretative processes as moderating influences need to continue to evaluate their validity. Another finding of the study is a significant main effect of school performance on smoking initiation --a relationship which has not been previously reported in a national longitudinal sample. This study also found support for depression as an antecedent to smoking initiation -- a relationship whose causal direction continues to be controversial. Continued exploration of the complex relationships between these social and individual factors may allow for the development of more effective evidence-based smoking prevention programs

The spread and control of HIV in southern Africa

HIV has disproportionately affected southern Africa. This region, which comprises 2% of the worlds population, is home to an estimated 34% of all people living with HIV, 29% of new HIV infections globally in 2010, and 30% of AIDS-related deaths. A strengthened response to the epidemic by countries in southern Africa in recent years has brought life-prolonging antiretroviral therapy to the majority of those in need of treatment, and declines from peak levels of HIV incidence over the past decade are a reason for optimism. But, in 2010, 770,000 new HIV infections occurred. A better understanding of why the epidemic has spread so severely in this region is required to inform strategies to reduce and eventually eliminate new HIV infections. This thesis uses data analysis and mathematical modelling to understand the interaction between behavioural and biological factors that may have contributed to the spread of HIV in southern Africa, and the implications of these for controlling the epidemic. It focuses specifically on two topics of recent attention for public health decision makers in southern Africa: concurrent sexual partnerships and HIV treatment as prevention. Chapters explore the interaction between high HIV infectiousness during primary HIV infection and concurrent sexual partnerships, describe and evaluate a consensus indicator for concurrency, develop a method to adjust for high levels of missing data in sexual behaviour surveys and examine trends in sexual behaviours in a high HIV prevalence population in South Africa, create a mathematical model to examine the potential impact of antiretroviral therapy on HIV incidence in hyperendemic settings, and systematically compare the predictions of twelve different mathematical models of the impact of HIV treatment as prevention in South Africa. Taken together, through these topics we come to understand more broadly the complexity of the epidemiological context in which HIV spreads in southern Africa.Open Acces

Inferring HIV incidence trends and transmission dynamics with a spatio-temporal HIV epidemic model

Reliable estimation of spatio-temporal trends in population-level HIV incidence is becoming an increasingly critical component of HIV prevention policy-making. However, direct measurement is nearly impossible. Current, widely used models infer incidence from survey and surveillance seroprevalence data, but they require unrealistic assumptions about spatial independence across spatial units. In this study, we present an epidemic model of HIV that explicitly simulates the spatial dynamics of HIV over many small, interacting areal units. By integrating all available population-level data, we are able to infer not only spatio-temporally varying incidence, but also ART initiation rates and patient counts. Our study illustrates the feasibility of applying compartmental models to larger inferential problems than those to which they are typically applied, as well as the value of data fusion approaches to infectious disease modeling.Comment: 28 pages, 9 figures, submitted to Epidemics

How will we get there? How will we know?

Ending AIDS by 2030 is a monumental challenge. Tracking progress as incidence reaches lower levels could be just as challenging. In The Lancet HIV Sabin Nsanzimana and colleagues report progress and highlight the challenges that lie ahead on both fronts. The Rwanda HIV Incidence Survey enumerated a nationally representative sample of 13 728 HIV-negative adults in 2013, and followed up a remarkable 92% of participants 1 year later. The investigators detected 35 HIV seroconversions at follow-up. Two findings are especially noteworthy

Impact of ART on the fertility of HIV-positive women in sub-Saharan Africa.

OBJECTIVE: Understanding the fertility of HIV-positive women is critical to estimating HIV epidemic trends from surveillance data and to planning resource needs and coverage of prevention of mother-to-child transmission services in sub-Saharan Africa. In the light of the considerable scale-up in antiretroviral therapy (ART) coverage over the last decade, we conducted a systematic review of the impact of ART on the fertility outcomes of HIV-positive women. METHODS: We searched Medline, Embase, Popline, PubMed and African Index Medicus. Studies were included if they were conducted in sub-Saharan Africa and provided estimates of fertility outcomes (live births or pregnancies) among women on ART relative to a comparison group. RESULTS: Of 2070 unique references, 18 published papers met all eligibility criteria. Comparisons fell into four categories: fertility of HIV-positive women relative to HIV-negative women; fertility of HIV-positive women on ART compared to those not yet on ART; fertility differences by duration on ART; and temporal trends in fertility among HIV-positive women. Evidence indicates that fertility increases after approximately the first year on ART and that while the fertility deficit of HIV-positive women is shrinking, their fertility remains below that of HIV-negative women. These findings, however, were based on limited data mostly during the period 2005-2010 when ART scaled up. CONCLUSIONS: Existing data are insufficient to characterise how ART has affected the fertility of HIV-positive women in sub-Saharan Africa. Improving evidence about fertility among women on ART is an urgent priority for planning HIV resource needs and understanding HIV epidemic trends. Alternative data sources such as antenatal clinic data, general population cohorts and population-based surveys can be harnessed to understand the issue

Soft drink intake and progression of radiographic knee osteoarthritis: data from the osteoarthritis initiative

Objectives: We examine the prospective association of soft drink consumption with radiographic progression of knee osteoarthritis (OA). Design: Prospective cohort study. Setting: This study used data from the osteoarthritis initiative (OAI). Participants: In OAI, 2149 participants with radiographic knee OA and having dietary data at baseline were followed up to 12, 24, 36 and 48 months. Measures The soft drink consumption was assessed with a Block Brief Food Frequency Questionnaire completed at baseline. To evaluate knee OA progression, we used quantitative medial tibiofemoral joint space width (JSW) based on plain radiographs. The multivariate linear models for repeated measures were used to test the independent association between soft drink intake and the change in JSW over time, while adjusting for body mass index and other potential confounding factors. Results: In stratified analyses by gender, we observed a significant dose–response relationship between baseline soft drink intake and adjusted mean change of JSW in men. With increasing levels of soft drink intake (none, ≤1, 2–4 and ≥5 times/week), the mean decreases of JSW were 0.31, 0.39, 0.34 and 0.60 mm, respectively. When we further stratified by obesity, a stronger dose–response relationship was found in non-obese men. In obese men, only the highest soft drink level (≥5 times/week) was associated with increased change in JSW compared with no use. In women, no significant association was observed. Conclusions: Our results suggest that frequent consumption of soft drinks may be associated with increased OA progression in men. Replication of these novel findings in other studies demonstrating the reduction in soft drink consumption leads to delay in OA progression is needed

Differential rates of perinatal maturation of human primary and nonprimary auditory cortex

Abstract Primary and nonprimary cerebral cortex mature along different timescales; however, the differences between the rates of maturation of primary and nonprimary cortex are unclear. Cortical maturation can be measured through changes in tissue microstructure detectable by diffusion magnetic resonance imaging (MRI). In this study, diffusion tensor imaging (DTI) was used to characterize the maturation of Heschl’s gyrus (HG), which contains both primary auditory cortex (pAC) and nonprimary auditory cortex (nAC), in 90 preterm infants between 26 and 42 weeks postmenstrual age (PMA). The preterm infants were in different acoustical environments during their hospitalization: 46 in open ward beds and 44 in single rooms. A control group consisted of 15 term-born infants. Diffusion parameters revealed that (1) changes in cortical microstructure that accompany cortical maturation had largely already occurred in pAC by 28 weeks PMA, and (2) rapid changes were taking place in nAC between 26 and 42 weeks PMA. At term equivalent PMA, diffusion parameters for auditory cortex were different between preterm infants and term control infants, reflecting either delayed maturation or injury. No effect of room type was observed. For the preterm group, disturbed maturation of nonprimary (but not primary) auditory cortex was associated with poorer language performance at age two years

Evaluating distributional regression strategies for modelling self-reported sexual age-mixing

The age dynamics of sexual partnership formation determine patterns of sexually transmitted disease transmission and have long been a focus of researchers studying human immunodeficiency virus. Data on self-reported sexual partner age distributions are available from a variety of sources. We sought to explore statistical models that accurately predict the distribution of sexual partner ages over age and sex. We identified which probability distributions and outcome specifications best captured variation in partner age and quantified the benefits of modelling these data using distributional regression. We found that distributional regression with a sinh-arcsinh distribution replicated observed partner age distributions most accurately across three geographically diverse data sets. This framework can be extended with well-known hierarchical modelling tools and can help improve estimates of sexual age-mixing dynamics