Expectation as a Risk for Covid-19-Related Olfactory Changes: Observations From the California Farmworkers Health Survey.

Some outcomes in medical and public health research, as well as clinical practice, must rely on patient reports and may be influenced by the prior knowledge of the patient. During the early months of the SARS-CoV-2 epidemic, changes in the sense of smell and taste were widely reported as a distinctive aspect of the new respiratory contagion. Using a Rubin Model of causal inference and data from a California Department of Public Health-sponsored survey of California farmworker health, we estimate that approximately half (56.5%) of infected patients reporting olfactory changes after a diagnosis of Covid-19 would not have reported olfactory changes if not made aware of their Covid-19 infection. The observations support a similar conclusion with respect to Covid-19-related changes in the sense of taste.