Adverse Events of Special Interest (AESI) and Related Risks: Anosmia, Ageusia

Anosmia and ageusia are considered neurological disorders, according to the list of events prioritized by SPEAC as potentially relevant to COVID-19 (1).

These are included because their effects are very common in cases of acute COVID-19 infection, and this has led to their being proposed as a way to screen for the disease. They are also known to occur in other respiratory viral infections such as influenza. According to ACCESS, ageusia is the loss of the taste functions of the tongue, while anosmia is the loss of the ability to detect one or more smells. The case definition of the ACCESS authors is as follows:

Anosmia: Absent smell function. There are two possible causes for anosmia: (i) conductive and/or traumatic; and (ii) sensorineural.

Ageusia: Absent taste function. A scale that ranges from 0, which refers to no taste, to 4, which refers to total taste loss, is used. 

Risk factors:

• Diseases and other factors:

Anosmia: Nasal obstructive disorders such as chronic rhinosinusitis, nasal polyposis, allergic rhinitis, and nasal masses can obstruct the flow of nasal air to olfactory clefts and cause decreased smell. Chronic rhinosinusitis can occur following vaccination. Approximately 20% to 30% of patients who have experienced head trauma develop some degree of olfactory dysfunction, with 5% experiencing anosmia. Thus, recent trauma should be excluded. In 20% to 30% of patients with olfactory dysfunctions, there is a recent history of upper respiratory infection. Damage to the olfactory bulb can occur from neurodegenerative diseases such as Alzheimer's and Parkinson's. Anosmia as part of another disease should be excluded. 

Ageusia: Damage to taste nerves, dietary deficiencies, systemic conditions such as hypothyroidism, diabetes mellitus, pernicious anemia, Sjogren's syndrome and Crohn's disease, cranial nerve injuries (neuritis due to herpes zoster, meningioma or neurinomas), skull base tumors, etc. Patients with cancer of any part of the head or neck who are receiving radiation therapy. Inflammation from burns, lacerations, surgery, and local anesthesia. Local antiplaque medications and certain dental infections, dentures, dental restorations, etc. In addition, factors associated with aging can affect the gustatory system.

• Medications:

Anosmia: Many drugs, such as antihypertensives and antihyperlipidmics, can be associated with smell disorders. Angiotensin converting enzyme inhibitors, diuretics, calcium channel blockers, and statins; amphetamines, enalapril, estrogen, phenothiazines, reserpine, and prolonged use of decongestants.  

Ageusia: Use of certain medications, such as antibiotics (ampicillin, macrolides, metronidazole, quinolones, tetracycline), antineoplastic agents, drugs to treat neurological disorders (anti-parkinsonian drugs, central nervous system stimulants, migraine medications), cardiovascular medications, antipsychotics, tranquilizers, tricyclic antidepressants, antihistamines, bronchodilators, antifungals, and antivirals have reported ageusia as an adverse event.  

• Vaccines in general: There is no reference to events associated with vaccines, except for influenza vaccine (2).
  Possible risk with COVID-19 vaccines.  

Sources:

1. ACCESS vACCines. COVID-19 – Monitoring ReadineSS: Anosmia, ageusia event definition Form CD. https://docs.google.com/document/d/1ktG7HrP1Kie-SpmVgyQpij5KiVUi9qx5/edit
2. Doty RL, Berman AH, Izhar M, et al. Influenza vaccinations and chemosensory function. Am J Rhinol Allergy.
   2014 Jan-Feb;28(1):50–3. doi: 10.2500/ajra.2014.28.3987. https://pubmed.ncbi.nlm.nih.gov/24717882/. PMID: 24717882.