RESUMEN
Respondent Driven Sampling study (RDS) is a population sampling method developed to study hard-to-reach populations. A sample is obtained by chain-referral recruitment in a network of contacts within the population of interest. Such self-selected samples are not representative of the target population and require weighing observations to reduce estimation bias. Recently, the Network Model-Assisted (NMA) method was described to compute the required weights. The NMA method relies on modeling the underlying contact network in the population where the RDS was conducted, in agreement with directly observable characteristics of the sample such as the number of contacts, but also with more difficult-to-measure characteristics such as homophily or differential characteristics according to the response variable. Here we investigated the use of the NMA method to estimate HIV prevalence from RDS data when information on homophily is limited. We show that an iterative procedure based on the NMA approach allows unbiased estimations even in the case of strong population homophily and differential activity and limits bias in case of preferential recruitment. We applied the methods to determine HIV prevalence in men having sex with men in Brazilian cities and confirmed a high prevalence of HIV in these populations from 3.8% to 22.1%.
Asunto(s)
Infecciones por VIH/epidemiología , Homosexualidad Masculina , Modelos Biológicos , Brasil/epidemiología , Simulación por Computador , Humanos , Masculino , Densidad de Población , Prevalencia , Encuestas y CuestionariosRESUMEN
Model-based epidemiological assessment is useful to support decision-making at the beginning of an emerging Aedes-transmitted outbreak. However, early forecasts are generally unreliable as little information is available in the first few incidence data points. Here, we show how past Aedes-transmitted epidemics help improve these predictions. The approach was applied to the 2015-2017 Zika virus epidemics in three islands of the French West Indies, with historical data including other Aedes-transmitted diseases (chikungunya and Zika) in the same and other locations. Hierarchical models were used to build informative a priori distributions on the reproduction ratio and the reporting rates. The accuracy and sharpness of forecasts improved substantially when these a priori distributions were used in models for prediction. For example, early forecasts of final epidemic size obtained without historical information were 3.3 times too high on average (range: 0.2 to 5.8) with respect to the eventual size, but were far closer (1.1 times the real value on average, range: 0.4 to 1.5) using information on past CHIKV epidemics in the same places. Likewise, the 97.5% upper bound for maximal incidence was 15.3 times (range: 2.0 to 63.1) the actual peak incidence, and became much sharper at 2.4 times (range: 1.3 to 3.9) the actual peak incidence with informative a priori distributions. Improvements were more limited for the date of peak incidence and the total duration of the epidemic. The framework can adapt to all forecasting models at the early stages of emerging Aedes-transmitted outbreaks.
Asunto(s)
Aedes/virología , Fiebre Chikungunya/transmisión , Epidemias , Modelos Estadísticos , Mosquitos Vectores/virología , Infección por el Virus Zika/transmisión , Animales , Fiebre Chikungunya/epidemiología , Fiebre Chikungunya/virología , Virus Chikungunya/aislamiento & purificación , Toma de Decisiones Clínicas , Brotes de Enfermedades , Epidemias/prevención & control , Humanos , Incidencia , Polinesia/epidemiología , Indias Occidentales/epidemiología , Virus Zika/aislamiento & purificación , Infección por el Virus Zika/epidemiología , Infección por el Virus Zika/virologíaRESUMEN
The recent global dissemination of Chikungunya and Zika has fostered public health concern worldwide. To better understand the drivers of transmission of these two arboviral diseases, we propose a joint analysis of Chikungunya and Zika epidemics in the same territories, taking into account the common epidemiological features of the epidemics: transmitted by the same vector, in the same environments, and observed by the same surveillance systems. We analyse eighteen outbreaks in French Polynesia and the French West Indies using a hierarchical time-dependent SIR model accounting for the effect of virus, location and weather on transmission, and based on a disease specific serial interval. We show that Chikungunya and Zika have similar transmission potential in the same territories (transmissibility ratio between Zika and Chikungunya of 1.04 [95% credible interval: 0.97; 1.13]), but that detection and reporting rates were different (around 19% for Zika and 40% for Chikungunya). Temperature variations between 22°C and 29°C did not alter transmission, but increased precipitation showed a dual effect, first reducing transmission after a two-week delay, then increasing it around five weeks later. The present study provides valuable information for risk assessment and introduces a modelling framework for the comparative analysis of arboviral infections that can be extended to other viruses and territories.
Asunto(s)
Fiebre Chikungunya/epidemiología , Fiebre Chikungunya/transmisión , Epidemias/estadística & datos numéricos , Infección por el Virus Zika/epidemiología , Infección por el Virus Zika/transmisión , Humanos , Polinesia/epidemiología , Indias Occidentales/epidemiología , Virus ZikaRESUMEN
OBJECTIVES: To test the hypothesis that multiple constituents of the apical plasma membrane residing alongside the causal cystic fibrosis (CF) transmembrane conductance regulator protein, including known CF modifiers SLC26A9, SLC6A14, and SLC9A3, would be associated with prenatal exocrine pancreatic damage as measured by newborn screened (NBS) immunoreactive trypsinogen (IRT) levels. STUDY DESIGN: NBS IRT measures and genome-wide genotype data were available on 111 subjects from Colorado, 37 subjects from Wisconsin, and 80 subjects from France. Multiple linear regression was used to determine whether any of 8 single nucleotide polymorphisms (SNPs) in SLC26A9, SLC6A14, and SLC9A3 were associated with IRT and whether other constituents of the apical plasma membrane contributed to IRT. RESULTS: In the Colorado sample, 3 SLC26A9 SNPs were associated with NBS IRT (min P=1.16×10(-3); rs7512462), but no SLC6A14 or SLC9A3 SNPs were associated (P>.05). The rs7512462 association replicated in the Wisconsin sample (P=.03) but not in the French sample (P=.76). Furthermore, rs7512462 was the top-ranked apical membrane constituent in the combined Colorado and Wisconsin sample. CONCLUSIONS: NBS IRT is a biomarker of prenatal exocrine pancreatic disease in patients with CF, and a SNP in SLC26A9 accounts for significant IRT variability. This work suggests SLC26A9 as a potential therapeutic target to ameliorate exocrine pancreatic disease.
Asunto(s)
Antiportadores/genética , Fibrosis Quística/genética , Páncreas Exocrino/anomalías , Biomarcadores/sangre , Membrana Celular/metabolismo , Colorado , Regulador de Conductancia de Transmembrana de Fibrosis Quística/genética , Femenino , Francia , Predisposición Genética a la Enfermedad , Genotipo , Humanos , Recién Nacido , Modelos Lineales , Masculino , Mutación , Tamizaje Neonatal , Polimorfismo de Nucleótido Simple , Control de Calidad , Transportadores de Sulfato , Tripsinógeno/sangre , WisconsinRESUMEN
BACKGROUND: Quantitative assessment of multiple sexual partnerships and concurrency may help to elucidate the large observed differences in the prevalence of AIDS among population subgroups and countries. GOAL: The goals of the study were (1) to develop a global scale of dynamic patterns of sexual partnerships, including concurrency with new partners and stable concurrency; (2) to apply this scale to three Caribbean regions characterized by different cumulative rates of incidence of AIDS; and (3) to compare the concurrency rates given by this scale with those of other published methods. STUDY DESIGN: We defined an individual scale based on 6 patterns of sexual behavior over the previous 12-month period, by using a simple algorithm to combine 7 variables. We then applied this scale to cross-sectional data collected from men living in three French Caribbean regions: Guadeloupe, Martinique, and Guyana. RESULTS: We found that all adults of all age classes in the three regions studied frequently had multiple (>2) and concurrent partnerships. The patterns of sexual behavior in the three regions were consistent with the respective cumulative incidence rates of AIDS, and a lower rate of concurrency with new partners and a higher rate of stable partnership concurrency were noted in Martinique, especially among 45- to 59-year-olds. The rate of concurrent partnerships was found to depend on the criteria used to define them and on the observation period (a given moment, or a defined period). Our definition gave a higher rate of concurrency than previously published indicators. CONCLUSION: The proposed scale can be applied to easy-to-collect data in cross-sectional population surveys and takes into account a wide variety of behaviors, including different types of concurrency.