Since the beginning of the SARS-CoV-2 (COVID-19) pandemic in 2019, there have been over 770 million confirmed cases and 6.9 million deaths worldwide (1). The list of possible COVID-19 symptoms is extensive, with fever, shortness of breath, and coughing being amongst the virus’ most typical symptoms (2). Infection severity ranges from asymptomatic or mild for most, to severe or critical illness for an estimated 20% of patients (3). At least 10% of those who have survived COVID-19 infection have been observed to have long-lasting symptoms (generally referred to as Long COVID), although the actual number of people with long term symptoms is estimated to be much higher than 10% (4, 5).
Long COVID can be defined as the continuation or development of new symptoms three months after the initial infection, such as fatigue and shortness of breath. Symptoms should last for at least two months and have no other likely explanation (6). Long COVID can develop regardless of disease severity (7), and its presentation tends to be heterogenous (8). This heterogeneity can make it challenging to characterize, and to identify different at-risk populations (8). Therefore, a deeper understanding of the underlying mechanisms and risk factors of long COVID is crucial in order to improve early patient identification and prevention of long COVID.
Known risk factors for long COVID development include older age, female sex, and moderate-to-severe COVID-19 (9). Possibly, parts of the exposome could be associated with long COVID. The exposome can be defined as the measurable totality of environmental exposures (10). The external exposome comprises the built environment, the social environment, the physicochemical environment, and the lifestyle/food environment an individual is exposed to and could contribute to disease (11). Several studies investigated potential links between the external exposome and COVID outcomes. Previous research has observed associations between the urban exposome and COVID-19 severity and mortality (12). Furthermore, low socioeconomic status (13) and exposure to ambient air pollution were found to be associated to long COVID (14-15). However, none have studied the exposome in a comprehensive way, which is essential given the complex correlation structure and potential interactions between different aspects of the exposome.
This study aims to comprehensively probe the external exposome for potential environmental drivers of long-COVID, thereby improving our understanding of underlying mechanisms.