SummaryBackgroundSince late 2015, an epidemic of yellow fever has caused more than 7334 suspected cases in Angola and the Democratic Republic of the Congo, including 393 deaths. We sought to understand the spatial spread of this outbreak to optimise the use of the limited available vaccine stock.MethodsWe jointly analysed datasets describing the epidemic of yellow fever, vector suitability, human demography, and mobility in central Africa to understand and predict the spread of yellow fever virus. We used a standard logistic model to infer the district-specific yellow fever virus infection risk during the course of the epidemic in the region.FindingsThe early spread of yellow fever virus was characterised by fast exponential growth (doubling time of 5–7 days) and fast spatial expansion (49 districts reported cases after only 3 months) from Luanda, the capital of Angola. Early invasion was positively correlated with high population density (Pearson's r 0·52, 95% CI 0·34–0·66). The further away locations were from Luanda, the later the date of invasion (Pearson's r 0·60, 95% CI 0·52–0·66). In a Cox model, we noted that districts with higher population densities also had higher risks of sustained transmission (the hazard ratio for cases ceasing was 0·74, 95% CI 0·13–0·92 per log-unit increase in the population size of a district). A model that captured human mobility and vector suitability successfully discriminated districts with high risk of invasion from others with a lower risk (area under the curve 0·94, 95% CI 0·92–0·97). If at the start of the epidemic, sufficient vaccines had been available to target 50 out of 313 districts in the area, our model would have correctly identified 27 (84%) of the 32 districts that were eventually affected.InterpretationOur findings show the contributions of ecological and demographic factors to the ongoing spread of the yellow fever outbreak and provide estimates of the areas that could be prioritised for vaccination, although other constraints such as vaccine supply and delivery need to be accounted for before such insights can be translated into policy.FundingWellcome Trust.
Background and aimsUsing mathematical modeling to illustrate and predict how different heroin source-forms: “black tar” (BTH) and powder heroin (PH) can affect HIV transmission in the context of contrasting injecting practices. By quantifying HIV risk by these two heroin source-types we show how each affects the incidence and prevalence of HIV over time. From 1997 to 2010 PH reaching the United States was manufactured overwhelmingly by Colombian suppliers and distributed in the eastern states of the United States. Recently Mexican cartels that supply the western U.S. states have started to produce PH too, replacing Colombian distribution to the east. This raises the possibility that BTH in the western U.S. may be replaced by PH in the future.DesignWe used an agent-based model to evaluate the impact of use of different heroin formulations in high- and low-risk populations of persons who inject drugs (PWID) who use different types of syringes (high vs. low dead space) and injecting practices. We obtained model parameters from peer-reviewed publications and ethnographic research.ResultsHeating of BTH, additional syringe rinsing, and subcutaneous injection can substantially decrease the risk of HIV transmission. Simulation analysis shows that HIV transmission risk may be strongly affected by the type of heroin used. We reproduced historic differences in HIV prevalence and incidence. The protective effect of BTH is much stronger in high-risk compared with low-risk populations. Simulation of future outbreaks show that when PH replaces BTH we expect a long-term overall increase in HIV prevalence. In a population of PWID with mixed low- and high-risk clusters we find that local HIV outbreaks can occur even when the overall prevalence and incidence are low. The results are dependent on evidence-supported assumptions.ConclusionsThe results support harm-reduction measures focused on a reduction in syringe sharing and promoting protective measures of syringe rinsing and drug solution heating.
Background and Aims. Using mathematical modeling to illustrate and predict how different heroin source-forms: "black tar" (BTH) and powder heroin (PH) can affect HIV transmission in the context of contrasting injecting practices. By quantifying HIV risk by these two heroin source-types we show how each affects the incidence and prevalence of HIV over time. From 1997 to 2010 PH reaching the United States was manufactured overwhelmingly by Colombian suppliers and distributed in the eastern states of the United States. Recently Mexican cartels that supply the western U.S. states have started to produce PH too, replacing Colombian distribution to the east. This raises the possibility that BTH in the western U.S. may be replaced by PH in the future.Design. We used an agent-based model to evaluate the impact of use of different heroin formulations in high-and low-risk injecting drug user populations who use different types of syringes (high vs. low dead space) and injecting practices. We obtained model parameters from peer-reviewed publications and ethnographic research.Results. Heating of BTH, additional syringe rinsing, and subcutaneous injection can substantially decrease the risk of HIV transmission. Simulation analysis shows that HIV transmission risk may be strongly affected by the type of heroin used. We reproduced historic differences in HIV prevalence and incidence. The protective effect of BTH is much stronger in high-risk compared with low-risk populations. Simulation of future outbreaks show that when PH replaces BTH we expect a long-term overall increase in HIV prevalence. In a population of injectors with mixed low-and high-risk clusters we find that local HIV outbreaks can occur even when the overall prevalence and incidence are low. The results are dependent on evidencesupported assumptions. Conclusions.The results support harm-reduction measures focused on a reduction in syringe sharing and promoting protective measures of syringe rinsing and drug solution heating.
Background: Chronic obstructive pulmonary disease (COPD) is the third leading cause of mortality in the US with a disproportionate impact on low socioeconomic communities. Pulmonary rehabilitation (PR) is one of few interventions to improve quality of life and reduce hospitalizations for individuals with COPD. Yet, as this is a resource intensive intervention, it is less available in economically disadvantaged communities, which have the greatest disease burden. Our group has developed low-intensity PR (LiPR) program that aims to increase access to PR while maintaining fundamental components of exercise training, self-management, and social support. However, elements of poverty produce barriers that limit adherence. What are predisposing, enabling, and reinforcing factors driving adherence to a LiPR program? Methods: We conducted 30 semi-structured interviews (SSI) of individuals who attended LiPR to explore mechanisms of adherence. Questions were informed by social cognitive theory (behavioral capability, self-efficacy, and reinforcement) and the socioecological model (individual, interpersonal, and environmental-level factors). Three coders independently categorized excerpts into predisposing, enabling, and reinforcing factors to identify barriers and facilitators to adherence to LiPR and exercise. Results: Several common themes emerged across SSIs. Attending the LiPR program led participants to report an increase in the knowledge of their disease and the role of exercise in its management, combining to increase a sense of self-efficacy -all of which are predisposing factors to adherence. Most frequent barriers identified to LIPR were a lack of transportation and a lack of available personal time to attend the class. Social support was the most reliably mentioned driver of positive reinforcement, underlying the importance of developing community through shared experience. Conclusions: These interviews have helped to identify the most impactful factors of LIPR which will guide future adaptations to the program. Furthermore, they underly the importance of reliable transportation and the role of social support for adherence to LIPR for underserved populations.
Background: Chronic obstructive pulmonary disease (COPD) is the fourth leading cause of death in the United States, disproportionally affecting economically disadvantaged communities. Pulmonary rehabilitation (PR) is an important component in the management of COPD, with evidence showing improvement in quality of life, dyspnea, and decrease in hospital readmissions. Despite guideline recommendations and evidence supporting its effectiveness, access to PR by underserved communities has been challenging. In light of the need of rehabilitation, we created an alternative form of PR, the COPD Wellness Program. This low intensity PR (LiPR) preserves key components of rehabilitation: self-management, exercise training, and social support. We aim to assess the feasibility and acceptability of a 10-week COPD Wellness Program in a safety-net hospital. Methods: 39 participants with moderate to severe COPD were enrolled in a 10-week pre-post intervention pilot study. These weekly sessions were developed to build behavioral capability and self-efficacy through group and homebased exercise training, disease education, and social support. Exercise curriculum incorporated the use of pedometers, resistance bands, and home pulse oximeters to promote self-guided exercise at home. Outcomes measured included COPD assessment test (CAT), dyspnea-12 (D-12), 6-minute walk test (6-MWT) and Patient Health Questionnaire-8 (PHQ-8). Results: Twenty-six participants out of 39 (67%) completed more than 5 LiPR sessions, with 29/39 (74%) attending 12-month follow-up. The mean age of participants was 64 year (SD ± 1.12), with 44% of the population composed of women. There was significant improvement in CAT (pre 19.9 vs post 16.4, p = 0.0394) and PHQ-8 (pre 6.7 vs post 3.9, p = 0.0016). No statistical significance was seen in D-12 (pre 14.7 vs post 13.3, p = 0.3464) or 6-MWT (pre 351.2 vs post 352.0, p = 0.97). Conclusion: Low intensity pulmonary rehabilitation for patients with moderate to severe COPD in a safety-net hospital was feasible and associated with improvement in respiratory and depression symptoms, based in improvements in the CAT and PHQ-8 scores. Although there was no statistical significance in the other outcomes, further studies with larger sample size are needed to confirm the benefits of LiPR.
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