Table 3 Summary of the main results obtained from the articles included in the study

[15]

Clinical features of covid-19.

Olfactory disorders were observed in 53% of patients in a cohort study conducted in Italy.

[16]

Possible link between anosmia and COVID-19: sniffing out the truth.

Loss of smell and/or taste can be a consistent symptom of SARS-CoV-2 infection. In addition, nasal epithelial cells exhibit a very high expression of the ACE-2 receptor allowing the viral entry.

[17]

Defining the burden of olfactory dysfunction in COVID-19 patients.

The Department of Diseases at Hospital Luigi Sacco, in Milan, Italy, through a questionnaire with 59 patients hospitalized for COVID-19, found that approximately 35% of patients had olfactory or gustatory changes and 18.6% had both.

[18]

Early recovery following new onset anosmia during the COVID-19 pandemic - an observational cohort study.

Of 382 patients, 86.4% reported anosmia. Of these, 11.5% reported severe loss of smell. After a week of follow-up: 80.1% reported a decrease in the severity of the symptom, 17.1% reported no change and 1.9% worsened. After a new survey (one week later): 11.5% had achieved complete symptomatic resolution and 17.3% reported the persistence of the symptom for one to four weeks. There was a 79% recovery rate in the interval between searches.

[19]

Olfactory and gustatory dysfunctions as a clinical presentation of mild-to-moderate forms of the coronavirus disease (COVID-19): a multicenter European study.

Among 417 patients with mild to moderate COVID-19 infection, 357 (85.6%) reported olfactory disorders and 79.6% had anosmia.

[6]

Self-reported Olfactory and Taste Disorders in Patients With Severe Acute Respiratory Coronavirus 2 Infection: A Cross-sectional Study.

Among 59 patients, 20 (33.9%) reported at least one taste or olfactory disorder and 11 (18.6%) reported both.

[20]

Strong associations and moderate predictive value of early symptoms for SARS-CoV-2 test positivity among healthcare workers, the Netherlands, March 2020.

Anosmia was reported by 47% of those affected by SARS-CoV-2 and was strongly associated with positivity for SARS-CoV-2.

[21]

Are we facing a crashing wave of neuropsychiatric sequelae of COVID-19? Neuropsychiatric symptoms and potential immunologic mechanisms.

Olfactory epithelial cells express the ACE2 receptor, but the exact pathophysiology pathway of the anosmia in COVID-19 remains uncertain.

[8]

Anosmia, hyposmia, and dysgeusia as indicators for positive SARS-CoV-2 infection.

Anosmia has been expressed as a symptom in patients positive for SARS-CoV-2, ranging from 15% to 66% depending on the study.

[22]

Alteraciones Del Olfato En El Covid-19, Revisión De La Evidencia E Implicaciones En El Manejo De La Pandemia.

The authors reported that 85.6% (357/417) of patients with COVID-19 had olfactory changes, 68% in the form of anosmia and 18% with hyposmia. 11.8% of the patients had changes in their sense of smell before the onset of other symptoms.

[7]

Neurological manifestations and complications of COVID-19: A literature review.

An Iranian cohort found that anosmia and hyposmia were reported in 48.23% of the patients infected by the SARS-CoV-2. Among them, the onset of anosmia was sudden in 76.24%. However, a Chinese cohort reported impaired sense of smell in only 11 (5.1%) patients.

[1]

Neurologic complications of COVID-19.

Among patients hospitalized with COVID-19, neurological complications ranged from 6% to 36%. It is suggested that SARS-CoV-2 acts in a retrograde way along the olfactory nerve and olfactory bulb, which act as a bridge between the nasal epithelium and the central nervous system, which may explain anosmia.

[23]

Extrapulmonary manifestations of COVID-19: Radiologic and clinical overview.

Suggests that the cerebral involvement of SARS-CoV-2 occurs via the cribriform plaque by interaction with ACE2 receptors, which can lead to symptoms such as hyposmia or anosmia.

[24]

El COVID-19 también Afecta el Sistema Nervioso por una de sus Compuertas: El Órgano Vascular de la Lámina Terminal y el Nervio Olfatorio. Alerta Neurológica, Prueba de Disosmia o Anosmia Puede Ayudar a Un Diagnóstico Rápido.

It proposes that the neuroinvasive properties of COVID-19 are related to the interaction of the virus with the ACE2 receptor. Therefore, those who have an altered response to smell should be considered as suspect patients.

[10]

Olfactory Dysfunction in COVID-19.

It was observed in an Iranian study that 59 of the 60 patients hospitalized with COVID-19 had impaired smell. In a study in Italy, 64% of 202 mildly symptomatic patients reported olfaction deficiency.

[25]

The Prevalence of Olfactory and Gustatory Dysfunction in COVID-19 Patients: A Systematic Review and Meta-analysis.

Ten studies were analyzed for olfactory dysfunction (n = 1627), showing a prevalence of 52.73% among patients with COVID-19. It has been demonstrated that the use of validated methods of olfactory function considerably increases the detection of smell changes.

[26]

Smell Dysfunction: a biomarker for COVID-19.

It was observed that 98% of the 60 patients affected by COVID-19 exhibited some olfactory dysfunction. Of the 60 patients evaluated, 35 (58%) were anosmatic and only one had a normosmia (1/60; 2%). The other patients presented hyposmia.