Modelado y análisis de la epidemia de VIH-SIDA en Cuba

58 páginasPremio de Estudios Iberoamericanos La Rábida. Área Científico-Técnica 2007 (II Edición). En este trabajo se estudia la epidemia VIH-SIDA en Cuba desde una triple perspectiva: I) se analiza su dinámica de evolución a partir de un modelo de epidemia en Ecuaciones Diferenciales Ordinaria; II) se estiman los principales parámetros de la epidemia; y III) se lleva a cabo un análisis exploratorio de datos para evaluar la incidencia de la epidemia sobre determinados grupos de la población

A stochastic SIR model with contact-tracing: large population limits and statistical inference

A stochastic epidemic model accounting for the effect of contact-tracing on the spread of an infectious disease is studied. Precisely, individuals identified as infected may contribute to detecting other infectious individuals by providing information related to persons with whom they have had possibly infectious contacts. The population evolves through demographic, infection and detection processes, in a way that its temporal evolution is described by a stochastic Markov process, of which the component accounting for the contact-tracing feature is assumed to be valued in a space of point measures. For adequate scalings of the demographic, infection and detection rates, it is shown to converge to the weak deterministic solution of a PDE system, as a parameter n, interpreted as the population size roughly speaking, becomes large. From the perspective of the analysis of infectious disease data, this approximation result may serve as a key tool for exploring the asymptotic properties of standard inference methods such as maximum likelihood estimation. We state preliminary statistical results in this context. Eventually, relation of the model to the available data of the HIV epidemic in Cuba, in which country a contact-tracing detection system has been set up since 1986, is investigated and numerical applications are carried out

HIV with contact-tracing: a case study in Approximate Bayesian Computation

Missing data is a recurrent issue in epidemiology where the infection process may be partially observed. Approximate Bayesian Computation, an alternative to data imputation methods such as Markov Chain Monte Carlo integration, is proposed for making inference in epidemiological models. It is a likelihood-free method that relies exclusively on numerical simulations. ABC consists in computing a distance between simulated and observed summary statistics and weighting the simulations according to this distance. We propose an original extension of ABC to path-valued summary statistics, corresponding to the cumulated number of detections as a function of time. For a standard compartmental model with Suceptible, Infectious and Recovered individuals (SIR), we show that the posterior distributions obtained with ABC and MCMC are similar. In a refined SIR model well-suited to the HIV contact-tracing data in Cuba, we perform a comparison between ABC with full and binned detection times. For the Cuban data, we evaluate the efficiency of the detection system and predict the evolution of the HIV-AIDS disease. In particular, the percentage of undetected infectious individuals is found to be of the order of 40%

The HIV/AIDS epidemic in Cuba: description and tentative explanation of its low HIV prevalence

<p>Abstract</p> <p>Background</p> <p>The Cuban HIV/AIDS epidemic has the lowest prevalence rate of the Caribbean region. The objective of this paper is to give an overview of the HIV/AIDS epidemic in Cuba and to explore the reasons for this low prevalence.</p> <p>Methods</p> <p>Data were obtained from the Cuban HIV/AIDS programme established in 1983. This programme has an extensive adult HIV testing policy, including testing of all pregnant women. HIV and AIDS cases have been recorded since 1986. Persons found to be HIV-positive are interviewed on their sexual behaviour and partners. Tracing and voluntary testing of these partners are organised. Epidemiological description of this epidemic was obtained from analysis of this data set. Using elementary mathematical analyses, we estimated the coverage of the detection system (percentage of HIV-positive adults detected) and the average period between HIV infection and detection. Estimated HIV prevalence rates were corrected to account for the coverage.</p> <p>Results</p> <p>HIV prevalence has increased since 1996. In 2005, the prevalence among pregnant women was 1.2 per 10,000 (16/137000). Estimated HIV prevalence among 15- to 49-year-olds was 8.1 per 10,000 (4913/6065000; 95%CI: 7.9 per 10,000 – 8.3 per 10,000). Most (77%) of the HIV-positive adults were men, most (85.1%) of the detected HIV-positive men were reported as having sex with men (MSM), and most of the HIV-positive women reported having had sex with MSM. The average period between HIV infection and detection was estimated to be 2.1 years (IQR = 1.7 – 2.2 years). We estimated that, for the year 2005, 79.6% (IQR: 77.3 – 81.4%) of the HIV-positive persons were detected.</p> <p>Conclusion</p> <p>MSM drive the HIV epidemic in Cuba. The extensive HIV testing policy may be an important factor in explaining the low HIV prevalence. To reduce the HIV epidemic in Cuba, the epidemic among MSM should be addressed. To understand this epidemic further, data on sexual behaviour should be collected. Now that antiretroviral therapy is more widely available, the Cuban policy, based on intensive HIV testing and tracing of partners, may be considered as a possible policy to control HIV/AIDS epidemics in other countries.</p

Modeling secondary level of HIV contact tracing: its impact on HIV intervention in Cuba

<p>Abstract</p> <p>Background</p> <p>Universal HIV testing/treatment program has currently been suggested and debated as a useful strategy for elimination of HIV epidemic in Africa, although not without practical issues regarding the costs and feasibility of a fully implemented program.</p> <p>Methods</p> <p>A mathematical model is proposed which considers two levels of detection of HIV-infectives through contact tracing of known infectives in addition to detections through other means such as random screening. Simulations based on Cuban contact tracing data were performed to ascertain the potential impact of the different levels of contact tracing.</p> <p>Results</p> <p>Simulation studies illustrate that: (1) contact tracing is an important intervention measure which, while less effective than random screening, is perhaps less costly and hence ideal for large-scale intervention programs in developing countries with less resources; (2) the secondary level of contact tracing could significantly change the basic disease transmission dynamics, depending on the parameter values; (3) the prevalence of the epidemic at the time of implementation of contact tracing program might be a crucial factor in determining whether the measure will be effective in preventing disease infections and its eventual eradication.</p> <p>Conclusions</p> <p>Our results indicate that contact tracing for detection of HIV infectives could be suitably used to remedy inadequacies in a universal HIV testing program when designing timely and effective intervention measures.</p

Perilesional injections of autologous fat graft in burn healing

Introduction: Burns are devastating injuries and the appearance of hypertrophic scars is a frequent complication. The classic treatment of dermal burns offers unaesthetic results in healing; however, the literature reports that autologous fat grafts favor revascularization, epithelialization, and aesthetic improvement. Objective: To determine the results of the application of perilesional injections of autologous fat graft in patients with dermal burns. Methods: A quasi-experimental study was performed, without randomization. A non-probabilistic test was used and the sample was made up of 40 patients in 2 groups: Group I with 20 subjects who underwent injections of autologous fat and the classic burn cure and in Group II 20 subjects with only the classic burn cure. The variables mean epithelialization time, presence of unsightly scars, appearance of keloids and hypertrophic scars were evaluated. Results: The patients in group I, with injections of fat graft, had a mean epithelialization time of 10 days less than the 14 days in group II. In addition, less unsightly scars appeared and a lower tendency to the appearance of keloids and hypertrophic scars. Finally, the patients in the group had a lower score on the Patient and Observer Scar Assessment Scale (POSAS) scale. Conclusions: Perilesional autologous fat graft injections reduce the appearance of unsightly scars, decreasing epithelialization time and improving the vascularization, pigmentation, thickness, relief, elasticity and surface of the scar

Atrial fibrillation after cardiac surgery: Enunciation of a concept

Se realiza un análisis de la evolución de la clasificación y guías de tratamiento de la fibrilación auricular desde el 2006 hasta la fecha. Se estudia particularmente el caso de la fibrilación auricular posoperatoria, que puede entrar en varias de las clases de la clasificación actual y sobre la que no existe un concepto definido en la bibliografía revisada. Se enuncia un concepto de fibrilación auricular posoperatoria basado en la revisión de su fisiopatología. Se propone además, por las características que la diferencian de las otras como una sexta clase dentro de la clasificación actual de la fibrilación auricular. &nbsp; &nbsp;An analysis of the evolution of the classification and the treatment guidelines of atrial fibrillation from 2006 to the present was performed. The case of postoperative atrial fibrillation was particularly analyzed, which can be included in more than one class of the current classification and about which there is no concept defined in the literature reviewed. A concept of postoperative atrial fibrillation was enunciated based on the review of its pathophysiology and the author’s opinion. Based on the characteristics that differentiate it from the others, was suggested that it should be considered as a sixth class within the current classification of atrial fibrillation

Estimación de parámetros en modelos epidemiológicos de VIH/SIDA.

The validation process of mathematical models that describe practical applications usually implies the estimation of the unknown parameters that are involved. In this work, in order to estimates these parameters in the HIV/AIDS models of [7], the problem of estimatingthe parameters in first order ordinary differential equations with known start point is formulated and a strategy of solution is presented. It is verified as well, which is the model of HIV/AIDS that represents best the real data according with the strategy of solution.El proceso de validación de modelos matemáticos que describen aplicaciones prácticas implica, generalmente, la estimación de los parámetros desconocidos que en ellos intervienen. En este trabajo, con el fin de estimar estos parámetros en los modelos de VIH/SIDA de [7], se formula el problema de estimación de parámetros en ecuacionesdiferenciales ordinarias de primer orden con punto inicial conocido y se presenta una estrategia de solución al mismo. Se verifica, además, cuál es, en algún sentido, el modelo de VIH/SIDA que mejor representa los datos reales existentes según la estrategia de solución