Atmospheric characterization and time-series analysis of the impact of environmental factors on disease onset

Abstract

[eng] This thesis investigates the complex interplay between atmospheric characterization, environmental factors, and the onset of diseases, specifically focusing on Kawasaki Disease (KD) and COVID-19. Through time-series analysis and multidisciplinary approaches, it explores how air quality, climatic conditions, and airborne microbial diversity influence disease incidence and progression, offering new insights into the role of the environment in shaping public health outcomes. In the first study, we analyze the association between ultrafine aerosols enriched in metals—originating from intensive farming and urban pollution—and the incidence of KD in Japan. Utilizing daily variability data of fine aerosols and an unprecedented daily KD epidemiological record, we uncover a strong dynamical link. This suggests that exposure to these metal-rich aerosols may trigger immune responses leading to KD, accounting for over 40% of the disease’s variability and highlighting the significance of environmental triggers in its etiology. The second study examines the seasonality of KD through an age-stratified spatiotemporal analysis over a 20-year period in Japan. We identify significant temporal shifts in disease incidence, particularly an abrupt desynchronization between younger and older children after 2016. This shift is most evident in children under two years old, revealing a new autumn peak consistent across most regions. These findings suggest changes in environmental triggers and exposure windows, offering potential explanations for the mysterious patterns of this pediatric vasculitis. Expanding the scope, the third study explores the climatic signatures in the different COVID-19 pandemic waves across both hemispheres. By employing (and developing) statistical methods designed to detect transitory associations, we demonstrate strong consistent negative effects of temperature and absolute humidity on COVID-19 cases. Our findings classify COVID-19 as a seasonal low-temperature infection, emphasizing the role of climatic factors in its transmission dynamics and underscoring the importance of considering airborne pathways in public health interventions. The fourth study evaluates the diversity of microorganisms in aerosols above the planetary boundary layer, confirming the long-distance transport—up to 2,000 km—of viable human pathogens and antimicrobial-resistant bacteria. Through tropospheric aircraft surveys over Japan, we identify a vast array of bacterial and fungal taxa, including potential human pathogens originating from agricultural regions in Northeast Asia. This discovery highlights a novel pathway for disease dispersion and the need to consider atmospheric microbial communities in disease etiology and public health policies. The final study presents an innovative methodology for the real-time detection of bacteria in bioaerosols using Laser-Induced Fluorescence (LIF) and machine learning. By modifying existing equipment and testing with artificially generated aerosols enriched with different bacterial species, we achieve high accuracy in detecting (96.74%) and classifying (69.24% of class-balanced accuracy between 5 bacterial species) bacterial particles. This approach offers valuable tools for rapid monitoring of airborne microbial communities, enhancing both ecological studies and public health surveillance. Collectively, these studies provide a comprehensive examination of how atmospheric characterization and environmental factors influence disease onset. By bridging atmospheric science and epidemiology, this thesis contributes new perspectives on the environmental determinants of KD and COVID-19. It lays the groundwork for future research aimed at mitigating the impacts of air pollution, climate variability, and bioaerosol exposure on human health, with significant implications for public health strategies and policies.

[spa] Esta tesis explora la compleja relación entre factores ambientales, caracterización atmosférica y la aparición de enfermedades, centrándose en la enfermedad de Kawasaki (KD) y la COVID-19 como paradigmas de enfermedad (a priori) no comunicable y enfermedad infecciosa. A través de análisis de series temporales y enfoques multidisciplinarios, se investiga cómo la calidad del aire, el clima y la diversidad microbiana del aire influyen en la incidencia de estas enfermedades, ofreciendo nuevas perspectivas sobre el impacto ambiental en la salud pública. En el primer estudio se examina la relación entre aerosoles ultrafinos, enriquecidos con metales procedentes de la agricultura intensiva y la contaminación urbana, y la incidencia de KD en Japón. Los resultados muestran una fuerte correlación dinámica, lo que sugiere que estos aerosoles pueden desencadenar respuestas inmunitarias que explican una parte significativa de la variabilidad de la enfermedad. En el segundo estudio se enfoca en la estacionalidad de KD mediante un análisis espacio-temporal de 20 años, revelando un cambio abrupto en 2016, especialmente entre niños menores de dos años, que muestran un nuevo pico estacional en otoño en contra de lo que se observa en niños de otras edades y de todos los años previos. En el tercer estudio, se analiza la incidencia de COVID-19 a nivel global, demostrando que la enfermedad tiene un comportamiento estacional asociado a bajas temperaturas y humedad. Estos resultados resaltan el papel del clima en la transmisión de COVID-19. El cuarto estudio investiga el transporte a larga distancia de microorganismos a través de aerosoles, utilizando datos de un muestreo sin precedentes en la troposfera, confirmando que patógenos humanos viables pueden residir y ser transportados hasta 2000 km a través de corrientes troposféricas. Finalmente, en el quinto estudio se desarrolla un sistema de detección en tiempo real de bacterias en bioaerosoles utilizando técnicas de machine learning mediante la adaptación de equipos basados en fluorescencia láser, proporcionando una herramienta innovadora para el monitoreo de microorganismos en el aire. En conjunto, esta tesis ofrece una nueva comprensión de cómo los factores ambientales y atmosféricos influyen en la aparición de enfermedades, estableciendo conexiones entre la ciencia atmosférica y la epidemiología para mejorar las estrategias de salud pública.