Change in the sense of smell and taste is very common in patients with Covid-19, with an average of 40-50% of people reporting these symptoms globally, and up to 98% showing olfactory dysfunction when test objectively. These chemosensory deficits are often the only warning symptoms and the strongest predictors of SARS-CoV-2 infection.
Alterations in these senses may include decreased (hyposmia or hypogeusia) or absence of function (anosmia or ageusia), distorted (parosmia or parageusia) or putrefactive (cacosmia or cacogeusia) sensations, or even hallucinations (phantosmia or phantogeusia).
Although the change in the sense of smell and taste has been widely studied for its diagnostic value, little is known about the clinical course of such symptoms after Covid-19, with inconsistent evidence on the duration of recovery. In particular, it is unknown whether Covid-19-related chemosensory dysfunction is transient or permanent, and it is unclear what proportion of patients develop persistent dysfunction.
Furthermore, prognostic factors associated with recovery of smell and taste are unclear. While some studies have reported associations with baseline severity of dysfunction, age, and sex, not all studies are in agreement, and the roles of viral load, comorbid symptoms, and medical history have not been well studied.
Aim
To clarify in patients with covid-19 the rate of recovery of smell and taste, proportion with persistent dysfunction of smell and taste, and prognostic factors associated with the recovery of smell and taste.
Design
Systematic review and meta-analysis.
Data sources
PubMed, Embase, Scopus, Cochrane Library, and medRxiv from inception to October 3, 2021.
Review methods
Two blinded reviewers selected observational studies of adults (≥18 years) with Covid-19-related smell or taste dysfunction. Descriptive prognostic studies with time-to-event curves and prognostic association studies of any prognostic factor were included.
Data extraction and synthesis
Two reviewers extracted data, assessed study bias using QUIPS, and assessed quality of evidence using GRADE, following PRISMA and MOOSE reporting guidelines. Using iterative numerical algorithms, time-to-event individual patient data (IPD) were reconstructed and pooled to recover distribution-free summary survival curves, with recovery rates reported at 30-day intervals for participants who remained alive.
Main outcome measures
The primary outcomes were the proportions of patients who remained with smell or taste dysfunction. Secondary outcomes were odds ratios of prognostic variables associated with recovery of smell and taste.
Results
18 studies (3699 patients) from 4180 records were included in the reconstructed IPD meta-analyses. The risk of bias was low to moderate; Conclusions remained unchanged after exclusion of four high-risk studies. The quality of the evidence was moderate to high.
According to the parametric cure model, self-reported persistent smell and taste dysfunction could develop in 5.6 % (95% confidence interval: 2.7% to 11.0%, I 2 = 70%, τ 2 = 0.756, 95% prediction interval: 0.7% to 33.5%) and 4.4% (1.2% to 14.6%, I 2 =67%, τ 2=0.684, prediction interval 95%, 0.0% to 49.0%) of patients, respectively.
Sensitivity analyzes suggest that these could be underestimates. At 30, 60, 90, and 180 days, respectively, 74.1% (95% confidence interval, 64.0% to 81.3%), 85.8% (77.6% to 90.9% ), 90.0% (83.3% to 94.0%) and 95.7% (89.5% to 98.3%) of patients recovered their sense of smell (I 2 =0.0-77.2% , τ 2 =0.006-0.050) and 78.8% (70.5% to 84.7%), 87.7% (82.0% to 91.6%), 90.3% (83.5% to 94.3%) and 98.0% (92.2% to 95.5%) recovered their sense of taste (range of I 2 =0.0-72.1%, τ 2 =0.000-0.015).
Women were less likely to regain their sense of smell (odds ratio 0.52, 95% confidence interval 0.37 to 0.72, seven studies, I 2 = 20%, τ 2=0.0224) and taste ( 0.31 , 0.13 to 0.72, seven studies, I 2 =78%, τ 2 =0.5121) than men, and patients with greater initial severity of dysfunction (0.48, 0.31 to 0.73, five studies, I 2 = 10%, τ 2 < 0.001) or nasal congestion (0.42, 0.18 to 0.97, three studies, I 2 =0%, τ 2 <0.001) were less likely to regain their sense of smell.
Conclusions In this meta-analysis using parametric healing models of time-to-event data from 3699 patients in 18 studies, we identified a significant burden of long-term self-reported smell and taste abnormalities, with approximately 5% of patients developing dysfunction. persistent. This result could contribute to the growing burden of long Covid. Women were less likely to recover their sense of smell and taste. Patients with greater initial severity of dysfunction and patients with nasal congestion were also less likely to regain their sense of smell. Although most patients are expected to regain their sense of smell or taste within the first three months, a significant subpopulation of patients may develop long-lasting dysfunction. These patients require timely identification, personalized treatment, and long-term follow-up of associated sequelae. |
PROSPERO Systematic Review Registration CRD42021283922.
Comments
According to research, up to 5% of people suffer long-term problems with their sense of taste or smell after Covid infection. The international research team analyzed 18 observational studies in adults with Covid-related changes in smell or taste, involving 3,699 patients.
They found that:
- Loss of smell may persist in 5.6% of patients after recovery from Covid.
- 4.4% may not recover their sense of taste.
- At 30 days after initial infection, only 74% of patients reported recovery of smell and 79% of patients reported recovery of taste.
- Recovery rates increased with each passing month, peaking at 96% for smell and 98% for taste after six months.
- Women were less likely to regain their sense of smell and taste than men, while patients with greater initial severity of smell loss and those with nasal congestion were less likely to regain their sense of smell.
Among the study’s limitations, the researchers noted that it did not take into account which Covid variant the patients had recovered from. Patients are less likely to develop long Covid with the currently dominant Omicron virus strain, according to a large recent study.
Professor Danny Altmann, professor of immunology at Imperial College London, said: "This is a strong and important study, which alerts us once again to the difficulties inherent in mapping the scale of the long-term damage caused by Covid-19." .
’The authors performed a fairly rigorous meta-analysis across several cohorts, modeling taste and smell recovery time. It goes without saying that problems with taste and smell are not trivial to quality of life. This is part of a broader discussion about how we assess and address persistent changes collectively called Long Covid.
"Studies like this alert us to the hidden burden of people who suffer from persistent symptoms, but who perhaps didn’t think it was worth contacting their GP assuming there wouldn’t be much they could do."
The Office for National Statistics said in January that around 2% of the UK population - 1.3 million people - were experiencing Covid symptoms lasting more than four weeks after infection.
