Incidence of Loss of Smell with COVID-19
Loss of smell occurs in approximately 53-86% of COVID-19 patients, making it one of the most common and characteristic symptoms of the infection. 1, 2, 3
Reported Incidence Rates
The incidence of olfactory dysfunction in COVID-19 varies across studies but consistently demonstrates high prevalence:
- 59-86% of COVID-19 patients experience loss of taste and smell according to guideline-level evidence 1
- 53% prevalence reported in systematic analysis of affected individuals 2
- 33.9-68% incidence rate documented across multiple cross-sectional studies, with female patients experiencing higher rates 3
- 98.3% had objective olfactory dysfunction when tested with validated psychophysical testing (UPSIT), even though only 35% self-reported smell complaints 1
Clinical Presentation Patterns
Timing and Onset
- Anosmia typically develops 1-4 days after infection begins 1
- Can present as the initial or isolated symptom in 11.9-22% of cases, sometimes without any other respiratory symptoms 1
- In one case series, 3 of 35 patients (8.6%) had isolated anosmia as their sole presenting feature 1
Key Distinguishing Features
- Traditional nasal symptoms are often absent - patients typically lack congestion or rhinorrhea, unlike other viral upper respiratory infections 1
- Loss of taste usually reflects loss of retronasal olfaction (flavor perception) rather than true taste dysfunction 1, 4
- The WHO has added anosmia to its official symptom list, requiring self-isolation for affected individuals 4
Recovery Timeline
Recovery occurs in the majority but not all patients:
- 73% of patients improve within 7-14 days 1
- 44-73% report improvement within the first month 5, 6
- 20% have symptoms persisting beyond 14 days 1
- Some patients experience permanent dysfunction with no improvement at 6 months 1, 7
Parosmia Development
- 43.1% of patients develop parosmia (distorted smell perception) 7
- Median onset of parosmia is 2.5 months (range 0-6 months) after initial loss of smell 7
- Parosmia can occur even in patients who report partial recovery of olfactory function 7
Clinical Implications
Important pitfalls to avoid:
- Do not rely on patient self-reporting alone - objective testing reveals significantly higher rates of dysfunction than patients recognize 1
- Consider COVID-19 testing for any sudden-onset smell loss, especially when it presents as an isolated symptom without nasal congestion 5, 6
- Healthcare workers and close-contact workers with anosmia pose transmission risk since viral load is comparable between symptomatic and minimally symptomatic individuals 4
Recommended Management Approach
For persistent olfactory dysfunction beyond 4 weeks:
- Initiate olfactory training immediately and continue for minimum 3-6 months 5, 6
- Perform objective psychophysical testing using validated instruments (UPSIT or Sniffin'Sticks) rather than relying on patient assessment 6
- Re-evaluate at 1,3, and 6 months after treatment initiation 5, 6
- Refer to otolaryngology or specialized smell/taste clinic if no improvement after 3-6 months 5, 6