IL-6 affects the severity of olfactory disorder: A cross-sectional survey of 148 patients who recovered from Omicron infection using the Sniffin' Sticks test in Tianjin, China

Effective early strategy to prevent olfactory and gustatory dysfunction in COVID-19: a randomized controlled trial

BACKGROUND

Olfactory and gustatory dysfunctions (OGDs) are key symptoms of coronavirus disease 2019 (COVID-19), which may lead to neurological complications, and lack of effective treatment. This may be because post-disease treatments may be too late to protect the olfactory and gustatory functions.

AIM

To evaluate the effectiveness of early use of saline nasal irrigation (SNI), corticosteroid nasal spray, and saline or chlorhexidine gluconate mouthwash for preventing OGDs in COVID-19.

DESIGN

This study was a double-blind randomized controlled trial.

METHODS

The study was conducted from 5 May to 16 June 2022. We recruited patients from three hospitals who were admitted with COVID-19 but without OGDs on the day of admission. Olfactory and gustatory functions were evaluated using the Taste and Smell Survey and the numerical visual analog scale. Participants were randomized to the saline, drug or control groups. The control group received no intervention, saline group received SNI plus saline nasal spray and mouthwash, and the trial group received SNI plus budesonide nasal spray and chlorhexidine gluconate mouthwash. Participants were assessed again on the day of discharge.

RESULTS

A total of 379 patients completed the trial. The prevalence of OGDs was significantly lower in the saline (11.8%, 95% CI, 6.6-19.0%; P < 0.001) and drug (8.3%, 95% CI, 4.1-14.8%; P < 0.001) groups than in the control group (40.0%, 95% CI, 31.8-48.6%). Additionally, both interventions reduced the severity of OGDs.

CONCLUSIONS

We demonstrated effective strategies for preventing COVID-19-related OGDs, and the findings may guide early management of severe acute respiratory disease coronavirus 2 (SARS-CoV-2) infection to reduce the incidence of COVID-19-related complications.

Long-term olfactory loss post-COVID-19: Pathobiology and potential therapeutic strategies

An acute loss of smell emerged as a striking symptom present in roughly half of the people infected with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus in the early phases of the COVID-19 pandemic. In most COVID-19 patients, olfaction recovers over the course of a few weeks. However, a lasting partial or complete loss of smell, often associated with distorted olfactory perceptions termed parosmia, has emerged as a widespread problem impacting at least 5%-10% of those who experience anosmia due to COVID-19. Our inability to offer effective therapies to this hyposmic or anosmic population, comprising millions of patients, highlights an enormous unmet need for the medical system. Here, we summarize the current understanding of the pathobiology causing acute olfactory loss due to SARS-CoV-2 infection, focusing on how the virus interacts with the peripheral olfactory system, a major site of viral infection. We also explore the problem of long-COVID olfactory dysfunction, which may accompany other persistent systemic disorders collectively termed postacute sequelae of COVID-19. Specifically, we discuss an emerging model focused on unresolved immune cell activity driving ongoing dysfunction. Finally, we review current and future therapeutic approaches aimed at restoring olfactory function.

Subjective Smell Disturbances in Children with Sars-Cov-2 or Other Viral Infections do not Correspond with Olfactory Test Results

BACKGROUND

Olfactory dysfunction associated with SARS-CoV-2 infection in children has not been verified by a validated olfactory test. We aimed to determine whether these complaints are objectifiable (test-based hyposmia), how often they occur during acute SARS-CoV-2 infection compared to other upper respiratory tract infections (URTI), as well as in children recovered from COVID-19 compared to children with long COVID.

METHODS

Olfactory testing (U-sniff test; hyposmia<8 points) and survey-based symptom assessments were performed in 434 children (5-17 years; 04/2021-06/2022). 186 symptom-free children served as controls. Of the children with symptoms of acute respiratory tract infection, SARS-CoV-2 PCR test results were positive in 45 and negative in 107 children (URTI group). Additionally, 96 children were recruited at least 4 weeks (17.6±15.2 weeks) after COVID-19, of whom 66 had recovered and 30 had developed long COVID.

RESULTS

Compared to controls (2.7%), hyposmia frequency was increased in all other groups (11-17%, p<0.05), but no between-group differences were observed. Only 3/41 children with hyposmia reported complaints, whereas 13/16 children with complaints were normosmic, with the largest proportion being in the long-COVID group (23%, p<0.05).

CONCLUSION

Questionnaires are unsuitable for assessing hyposmia frequency in children. Olfactory complaints and hyposmia are not specific for SARS-CoV-2 infection. The number of complaints in the long-COVID group could result from aversive olfactory perception, which is undetectable with the U-sniff test.

Smell, taste and chemesthesis disorders in patients with the SARS-CoV-2 during Omicron variant pandemic in China

Chemosensory disorders (including smell, taste and chemesthesis) are among the established symptoms of COVID-19 infection; however, new data indicate that the changes in chemosensory sensation caused by COVID-19 may differ among populations and COVID-19 variants. To date, few studies have focused on the influence of the SARS-CoV-2 Omicron variant on qualitative changes and quantitative reductions in chemosensory function in China. We conducted a cross-sectional study of patients with COVID-19 caused by the Omicron variant, to investigate the prevalence of chemosensory disorders and chemosensory function before and during infection, using an online questionnaire. A total of 1245 patients with COVID-19 completed the survey. The prevalence rates of smell, taste, and chemesthesis disorders were 69.2%, 67.7%, and 31.4%, respectively. Our data indicate that sex, age, smoking, and COVID-19-related symptoms, such as lack of appetite, dyspnea, and fatigue, may be associated with chemosensory disorders during COVID-19. Self-rating of chemosensory function revealed that patients experienced a general decline in smell, taste, and chemesthesis function. Further longitudinal research studies are needed to generate additional data based on objective assessment and investigate the factors influencing chemosensory function in COVID-19.

The immune mechanism of the nasal epithelium in COVID-19-related olfactory dysfunction

During the first waves of the coronavirus disease 2019 (COVID-19) pandemic caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection, olfactory dysfunction (OD) was reported as a frequent clinical sign. The nasal epithelium is one of the front-line protections against viral infections, and the immune responses of the nasal mucosa may be associated with OD. Two mechanisms underlying OD occurrence in COVID-19 have been proposed: the infection of sustentacular cells and the inflammatory reaction of the nasal epithelium. The former triggers OD and the latter likely prolongs OD. These two alternative mechanisms may act in parallel; the infection of sustentacular cells is more important for OD occurrence because sustentacular cells are more likely to be the entry point of SARS-CoV-2 than olfactory neurons and more susceptible to early injury. Furthermore, sustentacular cells abundantly express transmembrane protease, serine 2 (TMPRSS2) and play a major role in the olfactory epithelium. OD occurrence in COVID-19 has revealed crucial roles of sustentacular cells. This review aims to elucidate how immune responses of the nasal epithelium contribute to COVID-19-related OD. Understanding the underlying immune mechanisms of the nasal epithelium in OD may aid in the development of improved medical treatments for COVID-19-related OD.

Prevalence of Olfactory Dysfunction with the Omicron Variant of SARS-CoV-2: A Systematic Review and Meta-Analysis

The omicron variant is thought to cause less olfactory dysfunction than previous variants of SARS-CoV-2, but the reported prevalence differs greatly between populations and studies. Our systematic review and meta-analysis provide information regarding regional differences in prevalence as well as an estimate of the global prevalence of olfactory dysfunction based on 62 studies reporting information on 626,035 patients infected with the omicron variant. Our estimate of the omicron-induced prevalence of olfactory dysfunction in populations of European ancestry is 11.7%, while it is significantly lower in all other populations, ranging between 1.9% and 4.9%. When ethnic differences and population sizes are considered, the global prevalence of omicron-induced olfactory dysfunction in adults is estimated to be 3.7%. Omicron's effect on olfaction is twofold to tenfold lower than that of the alpha or delta variants according to previous meta-analyses and our analysis of studies that directly compared the prevalence of olfactory dysfunction between omicron and previous variants. The profile of the prevalence differences between ethnicities mirrors the results of a recent genome-wide association study that connected a gene locus encoding an odorant-metabolizing enzyme, UDP glycosyltransferase, to the extent of COVID-19-related loss of smell. Our analysis is consistent with the hypothesis that this enzyme contributes to the observed population differences.

Prevalence of Olfactory Dysfunction with the Omicron Variant of SARS-CoV-2: A Systematic Review and Meta-analysis

The omicron variant is thought to cause less olfactory dysfunction than previous variants of SARS-CoV-2, but the reported prevalence differs greatly between populations and studies. Our systematic review and meta-analysis provide information about regional differences in prevalence as well as an estimate of the global prevalence of olfactory dysfunction based on 62 studies reporting on 626,035 patients infected with the omicron variant. Our estimate of the omicron-induced prevalence of olfactory dysfunction in populations of European ancestry is 11.7%, while it is significantly lower in all other populations, ranging between 1.9% and 4.9%. When ethnic differences and population sizes are taken into account, the global prevalence of omicron-induced olfactory dysfunction in adults is estimated at 3.7%. Omicron’s effect on olfaction is twofold to tenfold lower than that of the alpha or delta variant, according to previous meta-analyses and our analysis of studies that directly compared prevalence of olfactory dysfunction between omicron and previous variants. The profile of prevalence differences between ethnicities mirrors the results of a recent genome-wide association study that implicated a gene locus encoding an odorant-metabolizing enzyme, UDP glycosyltransferase, to be linked to the extent of COVID-related loss of smell. Our analysis is consistent with the hypothesis that this enzyme contributes to the observed population differences.