Anosmia and Covid-19

Around 10-15% of patients with acquired anosmia have Post Viral Olfactory Loss (PVOL). Coronaviruses are a known cause for anosmia. At the onset of the COVID-19 pandemic, reports from China, South Korea, US and Europe suggest that a significant proportion of COVID-19 patients describe a loss of smell and taste as the only symptoms or as part of mild flu-like symptoms. It is now well-established that these symptoms are important components of the COVID-19 sequelae with persistent dysfunction described in a subset of individuals.

For this study, individuals, mainly comprising mainly healthcare workers in the UK, with persistent and sudden loss of sense of smell (at least 4 weeks) were recruited to ascertain the prevalence of COVID-19 associated smell dysfunction. A positive COVID-19 test was not a requirement for participation if not readily available nor accessible, however, information regarding COVID-19 antigen and antibody testing was collected post-hoc from those for who data are readily available. All participants (n=227) underwent initial psychophysical smell testing using the Brief Smell Identification Test (BSIT), gustatory testing using Taste Strips and completed the Smell Qx questionnaire. This questionnaire collected relevant demographic information, medical history, details of COVID-19 symptoms experienced, as well as information on olfactory and gustatory function, including those related to quality-of-life.

Participants, who scored 8 or below on the BSIT (indicative of semi-quantitative smell loss) were further invited to participate in the early olfactory training randomized controlled trial. Participants were randomized to undergo either 12 weeks of olfactory training or receive safety information. At the end of the 12-weeks, participants completed a follow-up BSIT and survey.

All participants enrolled at baseline within the eligible timeframe, for whom a valid email address was available, were further invited to participate in 1 year follow-up assessments. This included all participants irrespective of baseline BSIT result and RCT participation. The follow-up included a final electronic survey and BSIT. In addition to questions related to their sense of smell, which were identical to those in the baseline and 12-week follow-up surveys, participants were also asked about any symptoms of long-Covid.