4.1 Prevalence of Olfactory Dysfunction in COVID-19 Positive Patients
Menni et al (in an unpublished paper made available before peer review) used the “COVID RADAR” symptom tracker app to extract a cohort of patients who had tested positive for COVID-19 and their associated symptomology. Over 1.5million people reported symptoms on this app but just 1702, who answered questions of loss of smell (and taste), were tested and 579 subsequently tested positive. This small proportion of their total population was the main limitation of this study. They then analysed the COVID-19 positive and negative groups for prevalence of symptoms. In the COVID-19 positive group 59.41% had experienced loss of smell compared to 18.97% in the negative group. For patients reporting loss of smell they report an odds ratio of 6.59 for a positive COVID-19 when compared to a negative result. They also analyse the impact of other independent symptoms, other than loss of smell (and taste), adjusting for age, sex and Body Mass Index (BMI). In their model loss of smell and taste was the strongest predictor of a COVID-19 positive result .
Lechian et al’s multi-centre study analysed patient and volunteer health care professionals’ who had a PCR positive result for COVID-19 with a questionnaire. Patients in the intensive care unit, patients with previous OD and those without a COVID-19 PCR result were excluded from analysis. The impact of OD was evaluated using a quality of life tool (sQOD-NS). 85.6% of their cohort of 417 patients reported OD. The majority self-rated as anosmic (79.6%) but others experienced hyposmia, phantosmia and parosmia. Anosmic patients were found to have a significantly lower sQOD-NS score compared with the hyposmic and normosmic individuals. This OD was not significantly associated with rhinorrhoea or nasal obstruction but a significant association was found with females being proportionally more affected than males. In the subgroup of patients who had clinically resolved infection the OD persisted in 63% of cases .
Yan et al sent an email invitation to complete a survey to 1480 patients who had undergone COVID-19 testing. They had a 58% response from COVID-19 positive patients and a 15% response from the negative group. Their survey evaluated patient reported symptoms with a focus on smell and taste. Sixty-eight percent of the COVIVD-19 positive group reported OD and similarly to Menni et al they found that loss of sense of smell (and taste) showed the largest magnitudes of association to COVID-19 positivity when compared with other symptoms. Seventy-two percent of the COVID-19 positive patients with OD reported improvement at the time of the survey .
Mao et al were one of the first groups to present the symptomology of patients presenting with a positive COVID-19 swab result. 5.1% of this group of 214 patients had experienced hyposmia. This was a retrospective analysis of electronic patient data and as such there is a risk that OD was not a symptom explored or documented in individual consultations within this cohort of patients. According to a “diagnostic criteria” that is not described they divided their patients in to severe and non-severe groups. Of the 11 patients who had reported hyposmia 3 were non-severe and 8 were severe .
Giacomelli et al interviewed 59 of 88 inpatients with COVID-19 demonstrated on PCR, there were 29 non-respondents due to receiving ventilation, dementia and linguistic barriers. They report combined rates of smell or taste disturbance and as such comparative incidence rates solely for OD was not possible to produce from the data presented. In their cohort the olfactory and gustatory disorders occurred in proportionally younger and more commonly female subjects and no patients had recovered at the time of interview. No data relating to time of interview following onset of symptoms is reported .
In the studies that investigated olfactory symptoms independently we present the prevalence rates in Table 2 to form a meta-analysis for the prevalence of OD in the population of patients that have tested positive.