Discussion
This is cross-sectional study highlights the prevalence and associations of COVID-19 with anosmia and ageusia, and their impact on patients’ life in the Kingdom of Bahrain, involving 405 patients infected between October 2020 and June 2021.
The study reported comparable rates of anosmia and dysgeusia, with almost half of the studied patients experiencing either or both symptoms. A combination of anosmia and dysgeusia was more prevalent than either of the symptoms presenting alone. olfactory and taste dysfunction following Covid-19 is possibly underreported in the literature, as most studies are based on self-reports rather than a more objective assessment.
Our study’s population had a significantly higher prevalence of anosmia/ dysgeusia amongst females in comparison with their male counterparts. Similar findings were observed in studies conducted in Saudi, Italy, and Switzerland (13,14). However, this variation between sexes was not significant in other studies (15-18). Possible reasons for this variation in results across studies are the differences in methodology, symptom definition, population studied, measurement tool and recall bias as data was mainly dependent on self-reporting of symptoms. The literature discusses potential biological differences between genders in ACE receptor expression and its location on the X-chromosome, and differences in baseline olfaction as possible explanations to the increased prevalence of these symptoms amongst females (19,20). Both human cell receptors ACE2 and TMPRSS2 are essential for the SARS-CoV-2 entrance. These receptors are mostly present in the olfactory epithelium cells. Therefore, the main hypothesis is that anosmia is caused due to damage to non-neuronal cells which, thereafter, affects the normal olfactory metabolism. A possible explanation for the higher prevalence among females would be that incomplete X chromosome inactivation would contribute to increased expression of ACE2 (21).
Symptoms related to smell and taste were generally associated with milder forms of the disease studied in the acute or initial phase (22). It is yet not clear if these symptoms have a higher impact on morbidity and mortality in the long term, especially with the possibility of neurological pathophysiology. Studies have reported significant associations of neurological burden and infection with SARS-CoV2, explaining the potential connection with entry through the olfactory bulb (23,24). In addition, recent studies demonstrated the association of microinvasive SARS-CoV2 and respiratory failure, emphasising the importance of future research on neurological impacts of COVID-19 (25,26).
In our study, smokers were more likely to experience loss of smell and taste compared to their non-smoking counterparts, although the difference was not found to be statistically significant. Other studies in the region reported significant association between smoking and both anosmia and dysgeusia (16,8). This difference could be explained by the self-reporting of smoking through a phone call, where people might be less comfortable reporting their behaviours (social acceptability bias).
Comparable rates of impact of anosmia and dysgeusia was reported by other studies (4,10,27,28). The main concerns were that the senses of taste and smell would not return, alteration of eating habits, feeling angry and difficulty performing daily activities. While greater attention is being paid to curbing other COVID-19 related symptoms as well as rolling out the vaccines, the prognosis of Covid-19 survivors with olfactory and taste dysfunction remains an enigma which will ultimately have a huge impact on patient’s quality of life especially if the loss or dysfunction is permanent.
Limitations of our study included measurement bias of some risk factors, recall bias, incomplete medical records, and missing information. Further, this study did not compare the impact of permanent vs transient loss/dysfunction of olfactory and taste. Strengths include random selection of an early cohort of COVID-19 patients from a national registry and using validated tool for outcome measurement.