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Menni et al (in an unpublished paper made available before peer review)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.