Treatment of HIV/AIDS at South Africa's Largest Employers: Myth and Reality

Background: In the past three years, many large employers in South Africa have announced publicly their intention of making antiretroviral treatment (ART) available to employees. Reports of the scope and success of these programs have been mostly anecdotal. This study surveyed the largest private sector employers in South Africa to determine the proportion of employees with access to ART through employer-sponsored HIV/AIDS treatment programs. Methods: All 64 private sector and parastatal employers in South Africa with more than 6,000 employees were identified and contacted. Those that agreed to participate were interviewed by telephone using a structured questionnaire. Results: 52 companies agreed to participate. Among these companies, 63% of employees had access to employer-sponsored care and treatment for HIV/AIDS. Access varied widely by sector, however. Approximately 27% of suspected HIV-positive employees were enrolled in HIV/AIDS disease management programs, or 4.4% of the workforce overall. Fewer than 4,000 employees in the entire sample were receiving antiretroviral therapy. In-house (employer) disease management programs and independent disease management programs achieved higher uptake of services than did medical aid schemes. Conclusions: Publicity by large employers about their treatment programs should be interpreted cautiously. While there is a high level of access to treatment, uptake of services is low and only a small fraction of employees medically eligible for antiretroviral therapy are receiving it.

INVESTIGATION OF BUBBLE DYNAMICS AND HEATING DURING FOCUSED ULTRASOUND INSONATION IN TISSUE-MIMICKING MATERIALS

The deposition of ultrasonic energy in tissue can cause tissue damage due to local heating. For pressures above a critical threshold, cavitation will occur in tissue and bubbles will be created. These oscillating bubbles can induce a much larger thermal energy deposition in the local region. Traditionally, clinicians and researchers have not exploited this bubble-enhanced heating since cavitation behavior is erratic and very difficult to control. The present work is an attempt to control and utilize this bubble-enhanced heating. First, by applying appropriate bubble dynamic models, limits on the asymptotic bubble size distribution are obtained for different driving pressures at 1 MHz. The size distributions are bounded by two thresholds: the bubble shape instability threshold and the rectified diffusion threshold. The growth rate of bubbles in this region is also given, and the resulting time evolution of the heating in a given insonation scenario is modeled. In addition, some experimental results have been obtained to investigate the bubble-enhanced heating in an agar and graphite based tissue- mimicking material. Heating as a function of dissolved gas concentrations in the tissue phantom is investigated. Bubble-based contrast agents are introduced to investigate the effect on the bubble-enhanced heating, and to control the initial bubble size distribution. The mechanisms of cavitation-related bubble heating are investigated, and a heating model is established using our understanding of the bubble dynamics. By fitting appropriate bubble densities in the ultrasound field, the peak temperature changes are simulated. The results for required bubble density are given. Finally, a simple bubbly liquid model is presented to estimate the shielding effects which may be important even for low void fraction during high intensity focused ultrasound (HIFU) treatment.