In El Salvador, chronic kidney disease had reached epidemic proportions towards the end of this century’s first decade. In 2011–2012, the Ministry of Health reported it was the leading cause of hospital deaths in men, the fifth in women, and the third overall in adult hospital fatalities. Farming was the most common occupation among men in dialysis (50.7%). By 2017, chronic kidney disease admissions had overwhelmed hospital capacity. In 2009, El Salvador’s Ministry of Health, Cuba’s Ministry of Public Health and PAHO launched a cooperative effort to comprehensively tackle the epidemic. The joint investigations revealed a total prevalence of chronic kidney disease in the adult population of farming communities higher than that reported internationally (18% vs.11%–14.8%), higher in men than in women (23.9% vs 13.9%) and higher in men who were farmers/farmworkers than in men who were not (31.3% vs. 14.8%). The disease was also detected in children. An association was found between chronic kidney disease and exposure to agrochemicals (OR 1.4–2.5). In 51.9% of all chronic kidney disease cases, traditional causes (diabetes, hypertension, glomerulopathies, obstructive nephropathies and cystic diseases) were ruled out and the existence of a particular form of chronic kidney disease of nontraditional etiology was confirmed (whose initial cases were reported as early as 2002). In the patients studied, functional alterations and histopathologic diagnosis confirmed a chronic tubulointerstitial nephritis; most presented with neurosensory hearing loss, altered tendon reflexes and tibial artery damage. The main results of this cooperation were the epidemiologic, physiopathologic, clinical and histopathologic characterization of chronic kidney disease of nontraditional etiology. This characterization facilitated case definition for the epidemic and led to the hypothesis of systemic toxicity from agrochemicals (e.g., paraquat, glyphosate), which particularly affect the kidneys and to which farmers/farmworkers (who may also become dehydrated in the fields) are most exposed. The research thus also laid the foundations for design of comprehensive intersectoral government actions to reduce cases and put an end to the epidemic. KEYWORDS Chronic kidney disease, chronic renal failure, tubulointerstitial nephritis, epidemiology, histopathology, international cooperation, agrochemicals, environmental pollutants, noxae, and pesticides, occupational health, PAHO; El Salvador, Cuba

Este trabajo contextualiza la epidemia de enfermedad renal crónica y la carga de enfermedad relacionada que afecta a las comunidades agrícolas de la América Central. Se analizan las dos hipótesis principales (estrés por calor y agroquímicos), se llama la atención acerca de las consecuencias del razonamiento dicotómico concerniente a la causalidad, y se precave sobre el potencial conflicto de intereses y su papel en “la construcción de la duda”. Se describen algunos errores metodológicos que comprometen los resultados de estudios anteriores y se advierte acerca del peligro de dilatar las acciones de la salud pública hasta que se alcance una comprensión concluyente en relación con las causas de la epidemia y de los mecanismos subyacentes. Se fundamenta la necesidad de un enfoque integral de los hechos históricos, epidemiológicos y sociales de la epidemia, para valorar críticamente los estudios existentes e incrementar el rigor denuevas investigaciones.

PALABRAS CLAVE Epidemiología, salud pública, enfermedad renal crónica, causalidad, epidemia, agricultura, medio ambiente, agroquímicos, pesticidas, estrés por calor, determinantes sociales de salud, América Central

This paper contextualizes the chronic kidney disease epidemic and related burden of disease affecting Central American farming communities. It summarizes the two main causal hypotheses (heat stress and agrochemicals), draws attention to the consequences of dichotomous reasoning concerning causality, and warns of potential conflicts of interest and their role in “manufacturing doubt.” It describes some methodological errors that compromise past study findings and cautions against delaying public health actions until a conclusive understanding is reached about the epidemic’s causes and underlying mechanisms. It makes the case for a comprehensive approach to the historical, social and epidemiological facts of the epidemic, for critically assessing existing studies and for enhanced rigor in new research.

KEYWORDS Epidemiology, public health, chronic kidney disease, causality, epidemic, agriculture, environment, agrochemicals, pesticides, heat stress, social determinants of health, Central America

One of the most common shortcomings in non-communicable disease risk factor surveillance, especially in prevalence studies, is sampling procedures, which can and do compromise accuracy and reliability of derived estimates. Moreover, sampling consumes significant time and resources. Since the early 1990s, risk factor surveys in Cienfuegos province, Cuba have paid particular attention to careful sampling methods. The new survey conducted in 2011 was not only statistically rigorous but introduced an innovative, more efficient method. This article provides a detailed description of the sample design employed to optimize resource use without compromising selection rigor.

KEYWORDS Sampling, descriptive studies, risk factors, non-communicable diseases, hypertension, Cuba