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Introduction: Tracing patients lost to follow-up (LTFU) from HIV care is widely practiced, yet we have little knowledge of its causal effect on care engagement. In a prospective, Zambian cohort, we examined the effect of tracing on return to care within 2 years of LTFU. Methods: We traced a stratified, random sample of LTFU patients who had received HIV care between August 2013 and July 2015. LTFU was defined as a gap of >90 days from last scheduled appointment in the routine electronic medical record. Extracting 2 years of follow-up visit data through 2017, we identified patients who returned. Using random selection for tracing as an instrumental variable (IV), we used conditional two-stage least squares regression to estimate the local average treatment effect of tracer contact on return. We examined the observational association between tracer contact and return among patient sub-groups self-confirmed as disengaged from care. Results: Of the 24,164 LTFU patients enumerated, 4380 were randomly selected for tracing and 1158 were contacted by a tracer within a median of 14.8 months post-loss. IV analysis found that patients contacted by a tracer because they were randomized to tracing were no more likely to return than those not contacted (adjusted risk difference [aRD]: 3%, 95% CI: -2%, 8%, p = 0.23). Observational data showed that among contacted, disengaged patients, the rate of return was higher in the week following tracer contact (IR 5.74, 95% CI: 3.78-8.71) than in the 2 weeks to 1-month post-contact (IR 2.28, 95% CI: 1.40-3.72). There was a greater effect of tracing among patients lost for >6 months compared to those contacted within 3 months of loss. Conclusions: Overall, tracer contact did not causally increase LTFU patient return to HIV care, demonstrating the limited impact of tracing in this program, where contact occurred months after patients were LTFU. However, observational data suggest that tracing may speed return among some LTFU patients genuinely out-of-care. Further studies may improve tracing effectiveness by examining the mechanisms underlying the impact of tracing on return to care, the effect of tracing at different times-since-loss and using more accurate identification of patients who are truly disengaged to target tracing. Keywords: causality; HIV; instrumental variable; lost to follow-up; retention in care; tracing, 1 I INTRODUCTION Consistent engagement in HIV care is critical for patient health [1-5] and achieving global epidemic control targets [6]. Retention is challenging, however, with approximately one-third of patients [...]

Objective To examine biomarkers of methylmercury (MeHg) intake in women and infants from seafood-consuming populations globally and characterize the comparative risk of fetal developmental, neurotoxicity. Methods A search was conducted of the published literature reporting total mercury (Hg) in hair and blood in women and infants. These biomarkers are validated proxy measures of MeHg, a neurotoxin found primarily in seafood. Average and high-end biomarkers were extracted, stratified by seafood consumption context, and pooled by category. Medians for average and high-end pooled distributions were compared with the reference level established by a joint expert committee of the Food and Agriculture Organization (FAO) and the World Health Organization (WHO). Findings Selection criteria were met by 164 studies of women and infants from 43 countries. Pooled average biomarkers suggest an intake of MeHg several times over the FAO/WHO reference in fish-consuming riparians living near small-scale gold mining and well over the reference in consumers of marine mammals in Arctic regions. In coastal regions of south-eastern Asia, the western Pacific and the Mediterranean, average biomarkers approach the reference. Although the two former groups have a higher risk of neurotoxicity than the latter, coastal regions are home to the largest number at risk. High-end biomarkers across all categories indicate MeHg intake is in excess of the reference value. Conclusion There is a need for policies to reduce Hg exposure among women and infants and for surveillance in high-risk populations, the majority of which live in low-and middle-income countries. Objectif Examiner les biomarqueurs de l'ingestion de methylmercure (MeHg) chez les femmes et les enfants des populations consommant des poisson et fruits de mer au niveau mondial et caracteriser le risque comparatif de la neurotoxicite sur le developpement du foetus. Methodes Une recherche a ete effectuee dans la documentation publiee rapportant les quantites totales de mercure (Hg) dans les cheveux et le sang des femmes et des enfants. Ces biomarqueurs ont ete valides comme etant des mesures indirectes du MeHg, une neurotoxine que l'on trouve principalement dans les poissons et fruits de mer. Les biomarqueurs moyens et terminaux ont ete extraits, stratifies par contexte de consommation de poisons et fruits de mer et groupes par categorie. Les medianes pour les distributions groupees des biomarqueurs moyens et terminaux ont ete comparees avec le niveau de reference etabli par un comite mixte d'experts de l'Organisation des Nations Unies pour l'alimentation et l'agriculture (FAO) et l'Organisation mondiale de la Sante (OMS). Resultats Les criteres de selection ont ete satisfaits par 164 etudes concernant des femmes et des enfants dans 43 pays. Les biomarqueurs moyens groupes suggerent une ingestion de MeHg plusieurs fois superieure a la reference FAO/OMS chez les riverains consommateurs de poissons et vivant a proximite d'une zone d'orpaillage a petite echelle et bien au-dela de la reference chez les consommateurs de mammiferes marins dans les regions arctiques. Dans les regions cotieres de l'Asie du Sud-Est, du Pacifique occidental et de la Mediterranee, les biomarqueurs moyens se rapprochent de la reference. Bien que les deux premiers groupes aient un risque de neurotoxicite plus important que les derniers groupes, les regions cotieres abritent le plus grand nombre de personnes a risque. Les biomarqueurs terminaux dans toutes les categories indiquent que l'ingestion de MeHg est superieure a la valeur de reference. Conclusion II y a un besoin de politiques pour reduire l'exposition au Hg chez les femmes et les enfants, ainsi que pour surveiller les populations a haut risque, dont la majorite vit dans les pays a revenu faible et intermediaire. Objetivo Examinar los biomarcadores de la Ingesta de metilmercurio (MeHg) en mujeres y ninos procedentes de poblaciones que consumen pescados y mariscos a nivel global y describir el riesgo comparativo de neurotoxicidad del desarrollo fetal. Metodos Se realizo una busqueda de la literatura publicada que informa sobre el mercurio total (Hg) en el cabello y la sangre de mujeres y ninos. Estos biomarcadores son medidas indirectas validadas de MeElg, una neurotoxina que se encuentra sobre todo en el pescado y marisco. Se extrajeron biomarcadores de gama media y alta, los cuales se estratificaron por. contexto de consumo de pescado y marisco y se agruparon por categorias. Se compararon las medianas de las distribuciones por grupos de gama media y alta con el nivel de referencia establecido por un comite mixto de expertos de la Organizacion para la Agricultura y la Alimentacion (FAO) y la Organizacion Mundial de la Salud (OMS). Resultados 164 estudios de mujeres y ninos de 43 paises cumplieron los criterios de seleccion. El grupo de biomarcadores de gama media indica una ingesta de MeHg varias veces superior a la referenda de la FAO/ OMS en los riberenos que consumen pescado que viven cerca de una pequena mina de oro, y muy superior a la referencia en los consumidores de mamiferos marinos en las regiones articas. En las regiones costeras del sudeste de Asia, el Pacifico occidental y el Mediterraneo, los biomarcadores de gama media se acercan a la referencia. Aunque el riesgo de neurotoxicidad es mayor en los dos grupos anteriores que en el ultimo, las regiones costeras albergan el mayor numero de personas en riesgo. En todas las categorias, los biomarcadores de alta gama Indican que la ingesta de MeHg es superior al valor de referencia. Conclusion Se necesitan politicasque reduzcan la exposicion al Hg entre mujeres y ninos, asi como una vigilancia en las poblaciones de alto riesgo, la mayoria de las cuales viven en paises de bajos y medianos ingresos., Introduction The World Health Organization (WHO) considers mercury (Hg) among the top 10 chemicals of 'major public health concern'. (1) Evidence of ubiquitous Hg contamination globally led to the recent [...]