Loss of smell is a well-established symptom of the COVID-19 disease, so much so that it can be used to diagnose the illness. While most people who suffer from olfactory dysfunction due to COVID-19 recover it quickly within four weeks for 79% of people . But some with long COVID-19 smell disorders are detected unpleasant odors months after catching the virus . Patients with the COVID-19 disease across my country and the world are reporting unpleasant changes to their sense of smell after a COVID-19 diagnosis. This differs from the loss of sense of smell and taste, which is a pretty common COVID-19 symptom. This study represented a large case series of COVID-19 patients with parosmia (268 patients) with a short period (7 months). The main outcomes of the current study were all patients were suffering from hyposmia (27, 10.1%) or anosmia (241, 89.9%) before the development of parosmia, alteration in the quality of life in the majority of cases (91.8%), and poor outcome at short-term follow-up with different modalities of treatment.
The daily perception of parosmia was unpleasant for the majority of our patients and was typically described as sewage, moldy socks, rotten eggs, citrus, and rotten meats. All patients could identify the triggering stimuli eliciting parosmia. The study revealed a single or multiple triggering stimulus in all patients. While the response to these stimuli in all cases was single. The main odorant triggers were most of the odors (46.64%), perfume (22.39%), any odor (10.45%), frying smell (10.45%), and meat (10.07%). This finding (single response to single or multiple triggering stimuli) was consistent with the previous study by Bonfils et al. . It is of utmost importance to consider this observation in a future study to understand the exact pathogenesis of the parosmia.
It is often to see patients suffering from parosmia in the early phases of resolution from quantitative olfactory dysfunction (anosmia and hyposmia), 2 to 3 months from the onset of COVID-19 disease . The mean duration of parosmia from the point of disappearance of anosmia or hyposmia in our study was 3.434 ± 0.4886 months, which is slightly higher than Hopkins et al. study (2.5 months) . However, the duration of parosmia in this and Hopkins et al. studies was much lower than Bonfils et al. study (63.0 ± 7.6 months) . This difference may be attributed to the difference in the causes of parosmia, COVID-19 disease in the current and Hopkins et al. studies, and the causes in Bonfils et al. study were upper respiratory tract infection (24 patients), sinonasal disease (8 patients), toxic chemical exposure (4 patients), neurological disorders (3 patients), head injury (2 patients), nasal operation (2 patients), the aging process (1 patient), and idiopathic causes (12 patients). However, it is not known why patients with parosmia due to COVID-19 infection are present earlier than other causes of parosmia?. It is logical that the duration of parosmia greatly affects the quality of life, but, the present study didn’t show such an association (P-value > 0.05). This contradiction might be due to the short period of parosmia and short-term follow-up in the study.
Quality of life was considered as altered if the patient reported a decrease in appetite or body weight or a change in mood. Alteration of the smell can affect the quality of life badly or maybe a sign of more serious health problems. In the present study, 91.8% of the patients had altered daily life that agrees with other studies . The study reported a highly statistically significant difference between the altered quality of life and the dysgeusia and type and severity of parosmia. But there was no significant association between the quality of life and other studied variables.
The mean age of the patients with olfactory disorders was ranged from 35.91-57 years . Our result reported a lower mean of age than the above-mentioned studies. This may be attributed to the difference in the geographical area, ethnicity, and the cause of olfactory dysfunction. Besides, the current study revealed that about 75% of the cases were females, which was similar to other investigations , but in contrast to the prior study . However, there was no significant difference (P- value > 0.05) between the age and gender and the state of the quality of life due to parosmia.
The job might be a risk factor for acquiring olfactory disorders. Lee et al.  from Korea reported a higher prevalence rate of olfactory disorders in certain jobs, automobile repair (45.1%), printing (69.7%), and shoemaking and plating (88.9%) workers in comparison to the offices' workers (21.2%). It is well-known that there is no one immune against the COVID-19 disease, but healthcare workers are more vulnerable . The prior study by Villarreal et al. reported a high prevalence rate (26%) of persistent olfactory dysfunction for more than one month among healthcare workers with COVID-19 infection , our study revealed that there were 3 (1.1%) cases of the healthcare workers with parosmia. The study didn't find an explanation for this contradiction. The highest occupation affected in the present study was a housewife (n = 150, 56%). This may be attributed to the highest proportion of our patients were females (75%). Moreover, this occupation carried a difficulty in cooking and difficulty in detecting the order of baby nappy. Besides, there was no statistically significant difference between the quality of life and the occupation in the current study (P-value > 0.05).
Vent et al. study used the rat as a model for the assessment of the olfactory epithelium after exposure to tobacco smoke for 12 weeks, smoke and ethanol for the final 5 weeks, or no exposure to both of them (control group). Positive staining on the immunohistochemical analysis of the olfactory epithelium for the caspase-3 enzyme indicates the olfactory cells undergoing apoptotic proteolysis. They concluded that the loss of smell is higher in smokers than non-smoker owing to the increment in the death of the olfactory sensory neurons by cigarette smoke . Hummel and Lötsch reported a significant negative impact of smoking on the recovery of smell disorders . However, our study didn't find a significant effect of smoking on the severity of parosmia, quality of life alteration, and recovery rate.
Despite, the present study represented the largest case series study, there are limitations to this study. Firstly, the present study depends on the self-reported acquisition of the parosmia from the participants. Short-term follow-up of the cases is a second limitation, therefore we cannot determine the actual recovery rate of the parosmia in patients with the COVID-19 disease.
In conclusion, the current study revealed a large number of parosmia in patients with COVID-19 disease in a short period in comparison with other studies of the case series that involved the parosmia due to causes other than COVID-19. The majority of our cases were a young age group, females, housewives, and nonsmokers. All cases were preceded by anosmia or hyposmia. The majority of the cases were also suffering from dysgeusia. The altered quality of life was significantly affected by the presence of dysgeusia and type and severity of parosmia, while it was not affected by other factors (age, gender, occupation, smoking habit, duration of the parosmia, and whether the parosmia was preceded by quantitive olfactory disorders or associated with nasal symptoms). The outcome of both modalities of the treatment (olfactory training with either local and systemic steroid or tonics) was poor at the short-term follow-up.