Linear and nonlinear stability analysis of binary viscoelastic fluid convection

The linear and weakly nonlinear stability analysis of the quiescent state in a viscoelastic fluid subject to vertical solute concentration and temperature gradients is investigated. The non-Newtonian behavior of the viscoelastic fluid is characterized using the Oldroyd model. Analytical expressions for the critical Rayleigh numbers and corresponding wave numbers for the onset of stationary or oscillatory convection subject to cross diffusion effects is determined. A stability diagram clearly demarcates non-overlapping regions of finger and diffusive instabilities. A Lorenz system is obtained in the case of the weakly nonlinear stability analysis. The effect of Dufour and Soret parameters on the heat and mass transports are determined and discussed. Due to consideration of dilute concentrations of the second diffusing component the route to chaos in binary viscoelastic fluid systems is similar to that of single-component (thermal) viscoelastic fluid systems. © 2013 Elsevier Inc.

"Well, not me, but other women do not register because..."- Barriers to seeking antenatal care in the context of prevention of mother-to-child transmission of HIV among Zimbabwean women: a mixed-methods study.

BACKGROUND: While barriers to uptake of antenatal care (ANC) among pregnant women have been explored, much less is known about how integrating prevention of mother-to-child transmission (PMTCT) programmes within ANC services affects uptake. We explored barriers to uptake of integrated ANC services in a poor Zimbabwean community. METHODS: A cross-sectional survey was conducted among post-natal women at Mbare Clinic, Harare, between September 2010 and February 2011. Collected data included participant characteristics and ANC uptake. Logistic regression was conducted to determine factors associated with ANC registration. In-depth interviews were held with the first 21 survey participants who either did not register or registered after twenty-four weeks gestation to explore barriers. Interviews were analysed thematically. RESULTS: Two hundred and ninety-nine participants (mean age 26.1 years) were surveyed. They came from ultra-poor households, with mean household income of US$181. Only 229 (76.6$10-increase in household income 1.02 (95% confidence interval, CI, 1.0-1.04), as was education which interacted with having planned the pregnancy (OR for planned pregnancy with completed ordinary level education 3.27 (95%CI 1.55-6.70). Divorced women were less likely to register than married women, OR 0.20 (95%CI 0.07-0.58). In the qualitative study, barriers to either ANC or PMTCT services limited uptake of integrated services. Women understood the importance of integrated services for PMTCT purposes and theirs and the babies' health and appeared unable to admit to barriers which they deemed "stupid/irresponsible", namely fear of HIV testing and disrespectful treatment by nurses. They represented these commonly recurring barriers as challenges that "other women" faced. The major proffered personal barrier was unaffordability of user fees, which was sometimes compounded by unsupportive husbands who were the breadwinners. CONCLUSION: Women who delayed/did not register were aware of the importance of ANC and PMTCT but were either unable to afford or afraid to register. Addressing the identified challenges will not only be important for integrated PMTCT/ANC services but will also provide a model for dealing with challenges as countries scale up 'treat all' approaches

Manuscript title: Facilitators and barriers to cotrimoxazole prophylaxis among HIV exposed babies: a qualitative study from Harare, Zimbabwe.

BACKGROUND: Implementation of cotrimoxazole prophylaxis (CTX-p) among HIV-exposed infants (HEI) is poor in southern Africa. We conducted a study to investigate barriers to delivery of CTX-p to HEI in Zimbabwe at each step of the care cascade. Here we report findings of the qualitative component designed to investigate issues related to adherence conducted among women identified as HIV positive whose babies were started on CTX-p postnatally. Of note, Zimbabwe also provided nevirapine prophylaxis for HIV exposed babies, so the majority were giving nevirapine and CTX-p to their babies. METHODS: Between Feb-Dec 2011, the first 20 HIV infected mothers identified were invited for in-depth interview 4-5months postnatally. Interviews were recorded, transcribed, translated and analysed thematically. RESULTS: All women desired their baby's health above all else, and were determined to do all they could to ensure their wellbeing. They did not report problems remembering to give drugs. The baby's apparent good health was a huge motivator for continued adherence. However, most women reported that their husbands were less engaged in HIV care, refusing to be HIV tested and in some cases stealing drugs prescribed for their wives for themselves. In two instances the man stopped the woman from giving CTX-p to the baby either because of fear of side effects or not appreciating its importance. Stigma continues to be an important issue. Mothers reported being reluctant to disclose their HIV status to other people so found it difficult to collect prescription refills from the HIV clinic for fear of being seen by friends/relatives. Some women reported that it was hard to administer the drugs if there were people around at home. Other challenges faced were stock-outs of CTX-p at the clinic, which occurred three times in 2011. The baby would then go without CTX-p if the woman could not afford buying at a private pharmacy. CONCLUSIONS: The study highlights that adherence knowledge and desire alone is insufficient to overcome the familial and structural barriers to maintaining CTX-p. Improving adherence to CTX-p among HEI will require interventions to improve male involvement, reduce HIV stigma in communities and ensure adequate supply of drugs

Informing targeted HIV self-testing: a protocol for discrete choice experiments in Malawi, Zambia and Zimbabwe

Introduction HIV self-testing (HIVST) is a new approach to HIV testing where a person collects his or her own specimen, performs an HIV test and interprets the result, either alone or with someone he or she trusts. It is becoming increasingly relevant as a complement to standard-of-care HIV testing and is now recommended by the World Health Organization. Few studies have explored user preferences around HIVST service delivery and optimal models for increasing uptake and linkage to care, particularly among hard-to-reach populations. This paper describes an ongoing study that uses discrete choice experiments (DCE) to identify key HIVST service characteristics that drive people’s willingness to self-test for HIV and link to care, measure the relative strength of user preferences, and explore preference heterogeneity in Southern Africa. Method and Analysis Two DCEs – one on HIVST delivery and one on linkage to care after a positive self-test – are being administered in Malawi, Zambia and Zimbabwe. The designs in each country were informed by a qualitative study, which identified key HIVST service characteristics that influence user decision-making and refined scenario presentations and illustrations. Following data collection, DCE data will be analysed using a multinomial logit model as well as latent class, nested logit and generalised mixed models to examine heterogeneity in preferences by sociodemographic background, HIV testing experience and sexual behaviour. Ethics and dissemination The study has been approved by the College of Medicine Research Ethics Committee in Malawi, the Biomedical Ethics Committee of the University of Zambia, the Medical Research Council of Zimbabwe and the Research Ethics Committee of the London School of Hygiene and Tropical Medicine. Findings from the study will be presented at international conferences and in peer-reviewed journals. The results will help inform the HIVST implementation strategy in Southern Africa, particularly among populations underserved by standard-of-care services, such as men and young women

Delivery of index-linked HIV testing for children: learnings from a qualitative process evaluation of the B-GAP study in Zimbabwe

Background Index-linked HIV testing for children, whereby HIV testing is offered to children of individuals living with HIV, has the potential to identify children living with undiagnosed HIV. The “Bridging the Gap in HIV Testing and Care for Children in Zimbabwe” (B-GAP) study implemented and evaluated the provision of index-linked HIV testing for children aged 2–18 years in Zimbabwe. We conducted a process evaluation to understand the considerations for programmatic delivery and scale-up of this strategy. Methods We used implementation documentation to explore experiences of the field teams and project manager who delivered the index-linked testing program, and to describe barriers and facilitators to index-linked testing from their perspectives. Qualitative data were drawn from weekly logs maintained by the field teams, monthly project meeting minutes, the project coordinator’s incident reports and WhatsApp group chats between the study team and the coordinator. Data from each of the sources was analysed thematically and synthesised to inform the scale-up of this intervention. Results Five main themes were identified related to the implementation of the intervention: (1) there was reduced clinic attendance of potentially eligible indexes due to community-based differentiated HIV care delivery and collection of HIV treatment by proxy individuals; (2) some indexes reported that they did not live in the same household as their children, reflecting the high levels of community mobility; (3) there were also thought to be some instances of ‘soft refusal’; (4) further, delivery of HIV testing was limited by difficulties faced by indexes in attending health facilities with their children for clinic-based testing, stigma around community-based testing, and the lack of familiarity of indexes with caregiver provided oral HIV testing; (5) and finally, test kit stockouts and inadequate staffing also constrained delivery of index-linked HIV testing. Conclusions There was attrition along the index-linked HIV testing cascade of children. While challenges remain at all levels of implementation, programmatic adaptations of index-linked HIV testing approaches to suit patterns of clinic attendance and household structures may strengthen implementation of this strategy. Our findings highlight the need to tailor index-linked HIV testing to subpopulations and contexts to maximise its effectiveness