SARS-CoV-2: exposure to high external doses as determinants of higher viral loads and of increased risk for COVID-19. A systematic review of the literature
The determinants of the risk of becoming infected by SARS-CoV-2, contracting COVID-19, and being affected by the more serious forms of the disease have been generally explored in merely qualitative terms. It seems reasonable to argue that the risk patterns for COVID-19 have to be usefully studied in quantitative terms too, whenever possible applying the same approach to the relationship 'dose of the exposure vs pathological response' commonly used for chemicals and already followed for several biological agents to SARS-CoV-2, too. Such an approach is of particular relevance in the fields of both occupational epidemiology and occupational medicine, where the identification of the sources of a dangerous exposure and of the web of causation of a disease is often questionable and questioned: it is relevant when evaluating the population risk, too. Specific occupational scenarios, basically involving health workers, exhibit important proportions of both subjects simply infected by SARS-CoV-2 and of ill subjects with, respectively, mild, moderate, and severe disease. Similar patterns have been described referring to various circumstances of community exposure, e.g., standing in crowded public places, travelling on crowded means of transport, living in accommodation or care homes, living in the same household as a COVID-19 case. The hypothesis that these findings are a consequence not only of high probabilities of exposure, but also of high doses (as a product of both intensity and duration, with possible autonomous effects of peaks of exposure) deserves to be systematically tested, in order to reconstruct the web of causation of COVID-19 individual and clustered cases and to cope with situations at critical risk for SARS-CoV-2, needing to be identified, mapped, and dealt with at the right time. A limited but consistent set of papers supporting these assumptions has been traced in the literature. Under these premises, the creation of a structured inventory of both values of viral concentrations in the air (in case and if possible, of surface contaminations too) and of viral loads in biological matrixes is proposed, with the subsequent construction of a scenario-exposure matrix. A scenario-exposure matrix for SARS-CoV-2 may represent a useful tool for research and practical risk management purposes, helping to understand the possibly critical circumstances for which no direct exposure measure is available (this is an especially frequent case, in contexts of low socio-economic level) and providing guidance to determine evidence-based public health strategies.
aerosol; blood; cross infection; crowding (area); disease transmission; environmental exposure; environmental monitoring; family size; fomite; human; indoor air pollution; institutionalization; isolation and purification; microbiology; occupational exposure; risk; risk assessment; time factor; traffic and transport; viremia; virology; virus load; Aerosols; Air Microbiology; Air Pollution, Indoor; COVID-19; Cross Infection; Crowding; Disease Transmission, Infectious; Environmental Exposure; Environmental Monitoring; Family Characteristics; Fomites; Humans; Infectious Disease Transmission, Patient-to-Professional; Institutionalization; Occupational Exposure; Risk; Risk Assessment; SARS-CoV-2; Time Factors; Transportation; Viral Load; Viremia