Abstract
To the Editor: Although face masks are believed to prevent transmission of SARS-CoV-2, there is limited evidence supporting this belief. Time-dependent processes that are influenced by viral infection may be used to assess prevention of viral transmission. Because COVID-19 presentations to emergency departments in Chicago are reportable, their time course is ideally suited for such assessment. As a rule, presentations of influenza-like illnesses to emergency departments in Chicago decline according to an empirical first-order process [2], the parameters of which are calculable from even limited paired data. Deviation from the theoretical 'decay' of those data, especially deviation that occurs coincident with, for example, the mandated wearing of face masks, can then be used for causal inference (Fig. 1).
NSTL