Monotonicity properties arising in a simple model of Wolbachia invasion for wild mosquito populations.

In this paper, we propose a simplified bidimensional Wolbachia infestation model in a population of Aedes aegypti mosquitoes, preserving the main features associated with the biology of this species that can be found in higher-dimensional models. Namely, our model represents the maternal transmission of the Wolbachia symbiont, expresses the reproductive phenotype of cytoplasmic incompatibility, accounts for different fecundities and mortalities of infected and wild insects, and exhibits the bistable nature leading to the so-called principle of competitive exclusion. Using tools borrowed from monotone dynamical system theory, in the proposed model, we prove the existence of an invariant threshold manifold that allows us to provide practical recommendations for performing single and periodic releases of Wolbachia-carrying mosquitoes, seeking the eventual elimination of wild insects that are capable of transmitting infections to humans. We illustrate these findings with numerical simulations using parameter values corresponding to the wMelPop strain of Wolbachia that is considered the best virus blocker but induces fitness loss in its carriers. In these tests, we considered multiple scenarios contrasting a periodic release strategy against a strategy with a single inundative release, comparing their effectiveness. Our study is presented as an expository and mathematically accessible tool to study the use of Wolbachia-based biocontrol versus more complex models.

Reversión del bypass gástrico: indicaciones y resultados quirúrgicos / Gastric bypass reversal: surgical indications and results

Resumen Introducción: Debido a su eficacia en el tratamiento de la obesidad mórbida, el bypass gástrico (BPG) sigue siendo una intervención realizada frecuentemente. Sin embargo, un grupo reducido de pacientes puede desarrollar complicaciones nutricionales y metabólicas que no logran controlarse con un tratamiento médico óptimo. En estos casos, puede ser necesario reestablecer la continuidad del tracto gastrointestinal por medio de la reversión del BPG (R-BPG). Objetivo: Presentar las indicaciones y resultados obtenidos en una serie de pacientes sometidos a una R-BPG. Materiales y Método: Identificación y evaluación retrospectiva de todos los pacientes sometidos a una R-BPG en nuestra institución de manera consecutiva. Se registraron las características demográficas y antropométricas de la cirugía original y al momento de la reversión. Las complicaciones se registraron de acuerdo con la clasificación de Clavien-Dindo. Resultados: Se identificaron 7 pacientes en los cuales se realizó una R-BPG. En 2 casos la reversión fue por síndrome de intestino corto, en 3 casos por hipoglicemias severas refractarias a manejo médico y en 2 casos por diarrea crónica. La mediana de edad al momento de la reversión fue de 55 años. La mediana de tiempo desde la cirugía original hasta el momento de la reversión fue de 77 meses. La mediana de estadía hospitalaria fue de 6 días. No hubo complicaciones Clavien-Dindo ≥ III. La R-BPG logró revertir en todos los casos las complicaciones nutricionales y metabólicas. Conclusión: La restauración de la continuidad del tracto gastrointestinal permite el control de las complicaciones nutricionales y metabólicas.

Introduction: Due to its efficacy in the treatment of morbid obesity, roux-en-y gastric bypass (RYGB) continues to be a frequently performed intervention. However, a small group of patients may develop nutritional and metabolic complications that cannot be controlled with optimal medical treatment. In these cases, it may be necessary to reestablish the continuity of the gastrointestinal tract by reversing the RYGB (R-RYGB). Aim: To present the indications and results obtained in a series of patients who underwent to R-RYGB. Materials and Method: Identification and retrospective evaluation of all patients who underwent consecutive R-RYGB in our institution. Demographic and anthropometric characteristics of the original surgery and at the time of the reversal were recorded. Complications were classified according to Clavien-Dindo classification. Results: Seven patients were identified in whom an R-RYGB was performed. In 2 cases the reversal was due to short bowel syndrome, in 3 cases due to severe hypoglycemia refractory to medical treatment and in 2 cases due to chronic diarrhea. The median age at the time of the reversal was 55 years. The median time from primary surgery to reversal was 77 months. The median hospital stay was 6 days. There were no Clavien-Dindo complications ≥ III. The R-RYGB was able to reverse nutritional and metabolic complications in all cases. Conclusion: Restoring the continuity of the gastrointestinal tract allows control of nutritional and metabolic complications.

Assessment of event-triggered policies of nonpharmaceutical interventions based on epidemiological indicators.

Nonpharmaceutical interventions (NPI) such as banning public events or instituting lockdowns have been widely applied around the world to control the current COVID-19 pandemic. Typically, this type of intervention is imposed when an epidemiological indicator in a given population exceeds a certain threshold. Then, the nonpharmaceutical intervention is lifted when the levels of the indicator used have decreased sufficiently. What is the best indicator to use? In this paper, we propose a mathematical framework to try to answer this question. More specifically, the proposed framework permits to assess and compare different event-triggered controls based on epidemiological indicators. Our methodology consists of considering some outcomes that are consequences of the nonpharmaceutical interventions that a decision maker aims to make as low as possible. The peak demand for intensive care units (ICU) and the total number of days in lockdown are examples of such outcomes. If an epidemiological indicator is used to trigger the interventions, there is naturally a trade-off between the outcomes that can be seen as a curve parameterized by the trigger threshold to be used. The computation of these curves for a group of indicators then allows the selection of the best indicator the curve of which dominates the curves of the other indicators. This methodology is illustrated with indicators in the context of COVID-19 using deterministic compartmental models in discrete-time, although the framework can be adapted for a larger class of models.

Modelling cost-effectiveness of syphilis detection strategies in prisoners: exploratory exercise in a Chilean male prison.

BACKGROUND: Syphilis, together with other sexually transmitted infections, remains a global public health problem that is far from controlled. People deprived of liberty are a vulnerable population. Control activities in prisons rely mostly on passive case detection, despite the existence of affordable alternatives that would allow switching to active case-finding strategies. Our objective was to develop a mathematical modelling framework for cost-effectiveness evaluation, from a health system perspective, of different approaches using rapid tests for the detection of syphilis in inmates' populations and to explore the results based on a Chilean male prison population. METHODS: A compartmental model was developed to characterize the transmission dynamics of syphilis inside a prison with the ongoing strategy (passive case detection, with VRDL + FTA-ABS), considering the entrance and exit of inmates over a 40 year period. The model allows simulation of the implementation of a reverse algorithm for the current situation (rapid test + VDRL), different screening strategies (entry point, massive periodically; both with rapid test + VDRL) and treatment of detected cases. The parameters for the exploratory exercise were obtained from systematic searches of indexed and grey literature and field work (EQ-5D questionnaire application and key actors interviews). Probabilistic sensitivity analysis was conducted to account for uncertainty in relevant parameters. RESULTS: The proposed framework allows the evaluation of different detection strategies. In this study, all the strategies were cost-effective in the baseline scenario when considering an ICER threshold of 1 Chilean GDP per capita (US$15,000). The strategies most likely to be cost-effective (over 80% probability) were: current situation with reverse algorithm, entry point screening and mass screening every two years; the latter was the most effective, achieving the lowest prevalence (0.7% and 1.7% over the period versus the 3% prevalence in the current situation). CONCLUSIONS: Mathematical modelling that considers the performance of different tests and detection strategies could be a useful tool for decision making. The exploratory results show the efficiency of adopting both the use of the rapid tests and performing active case detection to significantly reduce the burden of syphilis in Chilean prisons in the near future.

Comparison of performance in an anaerobic digestion process: one-reactor vs two-reactor configurations.

The present work compares two types of configurations for a two-reaction (acidogenesis and methanogenesis) anaerobic digestion model. These configurations are as follows: (i) a single bioreactor, where the acidogenesis and methanogenesis reactions occur inside and, (ii) two bioreactors connected sequentially, where each reaction occurs separately in each reactor. The mathematical models that describe the mentioned configurations are analyzed at steady state, comparing the following criteria: the stability of the processes (stability properties of desired equilibria) and soluble organic matter removal performance (substrate levels at steady states), concluding that separation of the reactions in two bioreactors does not improve the stability of the process nor the soluble organic matter removal capacity, unless the improvement of the growth functions of both microorganism populations is considerably important at the moment of separating them into two reactors.

On the steady state optimization of the biogas production in a two-stage anaerobic digestion model.

In this paper, we study the optimization problem of maximizing biogas production at steady state in a two-stage anaerobic digestion model, which was initially proposed in Bernard et al. (Biotechnol Bioeng 75(4):424-438, 2001). Nominal operating points, consisting of steady states where the involved microorganisms coexist, are usually referred to as desired operational conditions, in particular for maximizing biogas production. Nevertheless, we prove that under some conditions related to input substrate concentrations and microorganism biology, characterized by their growth functions, the optimal steady state can be the extinction of one of the two species. We provide some numerical examples of this situation.

Sustainable thresholds for cooperative epidemiological models.

In this paper, we introduce a method for computing sustainable thresholds for controlled cooperative models described by a system of ordinary differential equations, a property shared by a wide class of compartmental models in epidemiology. The set of sustainable thresholds refers to constraints (e.g., maximal "allowable" number of human infections; maximal "affordable" budget for disease prevention, diagnosis and treatments; etc.), parameterized by thresholds, that can be sustained by applying an admissible control strategy starting at the given initial state and lasting the whole period of the control intervention. This set, determined by the initial state of the dynamical system, virtually provides useful information for more efficient (or cost-effective) decision-making by exhibiting the trade-offs between different types of constraints and allowing the user to assess future outcomes of control measures on transient behavior of the dynamical system. In order to accentuate the originality of our approach and to reveal its potential significance in real-life applications, we present an example relying on the 2013 dengue outbreak in Cali, Colombia, where we compute the set of sustainable thresholds (in terms of the maximal "affordable" budget and the maximal "allowable" levels of active infections among human and vector populations) that could be sustained during the epidemic outbreak.

Tools for improving feeding strategies in a SBR with several species.

This paper analyzes feeding strategies in a sequential batch reactor (SBR) with the objective of reaching a given (low) substrate level as quickly as possible for a given volume of water. Inside the SBR, several species compete for a single substrate, which leads to a minimal time control problem in which the control variable is the feeding rate. Following Gajardo et al. (2008) SIAM J Control Optim 47(6):2827-2856, we allow the control variable to be a bounded measurable function of time combined with possible impulses associated with instantaneous dilutions. For this problem, the extremal trajectories of the singular arc type are characterized as the strategies used to maintain the substrate at a constant level. Since this optimization problem is difficult to solve, this characterization provides a valuable tool for investigating the optimality of various feeding strategies. Our aim is thus to illustrate the use of this tool by proposing potential optimal feeding strategies, which may then be compared with other more intuitive strategies. This aim was accomplished via several numerical experiments in which two specific strategies are compared.

Cirugía laparoscópica sin neumoperitoneo / Laparoscopic surgery without pneumoperitoneum

Presentamos nuestra experiencia en 17 procedimientos de cirugía laparoscópica sin neumoperitoneo. La aplicación de esta técnica ha implicado fabricar elementos de tracción de la pared abdominal como alambres y tractor regulable. Se han realizado 11 colecistectomías, 2 procedimientos urológicos y 4 ginecológicos. El análisis de este procedimiento ha demostrado tener una morbilidad menor que la técnica con neumoperitoneo, y una disminución considerable en los otros

Dilatación hidraúlica en ureteroscopia / Hydraulic dilatation in ureteroscopy

Se presenta una experiencia prospectiva de 100 uterosopías con el método de dilatación hidráulica, donde destacan fundamentalmente la excelente visibilidad y seguridad con que se puede efectuar el procedimiento, lo que se traduce en una importantísima reducción de los tiempos operatorios, en poder acceder cualquier segmento ureteral en forma rutinaria y rápida en la mayoría de los casos, pudiendo efectuarse esta técnica preferentemente con anestesia regional. Nuestro procentaje global de éxito fue de 89 por ciento. El porcentaje de complicaciones fue de 12 por ciento y no hubo complicaciones mayores o pérdidas de unidades renales

Electroestimulación transrrectal en disfunciones eyaculatorias / Transrectal electrostimulation in ejaculatory disfunction

Se presenta una experiencia prospectiva en el Servicio de Urología del Hospital Roy H. Glover, en la técnica de elctroestimulación transrectal en disfunciones eyaculatorias. Se aplicó la técnica en doce enfermos con ausencia de eyaculación, producto de traumatismos raquimedulares y operados de linfadenectomías lumboórticas por tumores de testículo. Se obtuvo en el 85 por ciento de los casos respuestas positivas tras el procedimiento. No se observaron complicaciones. No existe bibliografía nacional al respecto y la literatura internacional sobre el tema es escasa, por lo que esta experiencia abre importantes avances en esta severa causa de infertilidad

Actividad urinaria de la enzima gamma glutamil transpeptidasa y su relación con la infección urinaria / Urinary GGTP activity and urinary tract infection

Se midió la actividad de la G.G.T.P. en orina, con el propósito de observar su comportamiento en los distintos tipos de I.T.U. Se seleccionaron 24 mujeres, que consultaron en el Hospital Naval de Valparaíso, con síntomas de I.T.U. las cuales se dividieron en altas y bajas según los clásicos criterios clínicos. Como grupo control, se contó con mujeres sanas. La actividad de la G.G.T.P. en sangre y orina se midió en un analizador automático y el análisis estadístico mediante el test de Student. Catorce sufrieron I.T.U. alta, y su promedio de actividad en orina fue de 60 ñ 37.8 Uds/L; mientras que 10 sufrieron I.T.U baja, con un promedio de 14 ñ 8.5 Uds/L. La diferencia es estadísticamente significativa (p < 0.001). El grupo control (22 mujeres), tuvo un promedio de 19.9 ñ 7 Uds/L y una diferencia significativa sólo con el grupo de I.T.U. altas. Los resultados de este estudio preliminar demuestran una diferencia significativa en la actividad urinaria de la G.G.T.P. entre las dos formas de I.T.U., por lo que en el futuro este método sencillo, barato y no invasivo puede ser de utilidad en la localización del sitio de la I.T.U. en clínica