Covid-19: A New Cause for Taste and Smell Dysfunction

Abstract

Dysfunction of the sense of smell and taste may have severe
impact on quality of life and overall health. Detection of
bad smell in the local environment is a warning sign for a
person and a good smell is pleasurable in life. Similarly
sense of taste is also very important for pleasure and to
avoid intake of hazardous meal or drink. Unfortunately,
knowledge about the smell and taste dysfunction is very
limited and little work has been conducted in this field.
There is a long list of disorders and diseases that can affect
and disturb olfactory and gustatory functions, ranging from
the local to central neurological causes. Virtually any disease
of the nose or paranasal sinuses can cause hyposmia or
anosmia, the common being chronic rhino-sinusitis, atrophic
rhinitis, nasal polypi, allergic rhinitis or neoplasia. The
neurological causes may include any pathology that can
affect olfactory nerves, olfactory bulb and their central
connections or the primary olfactory cortex. A new cause
in the list is COVID-19 infection for which medical fraternity
is thriving hard to unveil the underlying mechanisms
responsible for producing features.
With the recent pandemic of COVID-19, there is an explosion
of patients in hospitals with varied symptoms from just fever
to multiple organ failure.1 A typical case of COVID-19
presents with fever and dry cough which may progress to
pneumonia.2 Majority of the symptoms are related with the
upper or lower respiratory tract involvement by the virus.
Various studies have been published emphasizing about new
and atypical symptoms of COVID-19 related with taste and
smell dysfunction.3,4 The incidence of olfactory dysfunction
have been reported in viral infections like rhinovirus,
parainfluenza virus, Epstein-Barr virus and corona virus in
the past as well.5,6 Though in COVID-19 patients, this smell
dysfunction is not related with nasal obstruction and nasal
discharge. Cases have been recorded where isolated taste
and smell loss is present with no other symptom of COVID-
19 like fever, rhinorrhoea, body ache, breathlessness or
cough etc.7
The objective assessment of olfactory and gustatory functions
are not routinely performed in general health/medical
checkup. The clinicians and physicians rely only on selfreporting of the symptom. Many of the patients are even
unaware of any dysfunction present in these two special
senses. According to one study from Europe, the olfactory
and taste dysfunction occurrence in COVID-19 patients is
around 85.6% and 88.8% respectively.8 A local study from
Pakistan showed association of anosmia in 43.75% and
ageusia in 31.25%.9 In addition, these smell and taste
dysfunction may appear before, during or even after
development of other typical symptoms of COVID-19. The
present data depicts that the incidence of these two symptoms
in European patients is much higher than the rest of the
world. As taste and smell loss can be the only and early
symptom of COVID-19, it should bear in mind when
considering differential diagnosis in such situation. The time
period for recovering from these two symptoms also varied
from days to weeks to months even after improving all other
symptoms.