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We read the studies by Jin et al 1 and Lin et al 2 regarding the GI manifestations in COVID-19 with great interest. Recently, alteration in taste (dysgeusia, hypogeusia, ageusia) or smell (dysosmia, hyposmia, anosmia) has been increasingly reported in Western patients with COVID-19.3–10 However, these symptoms were not reported from these two studies from China.1 2 Therefore, we conducted a systematic review and meta-analysis to assess the prevalence of taste or smell alteration in patients with COVID-19 and to calculate the accuracy of these symptoms in the prediction of COVID-19. We searched articles in the PubMed database from 1 January 2020 through 10 May 2020 using the keywords “COVID-19” and “taste” or “smell” without any limitations in the search fields (registration number: CRD42020187912).
Of the 48 articles identified using the above search strategy, 30 were excluded (9 irrelevant, 9 comments, 5 review articles, 5 case reports, 2 series of cases with taste/smell alteration) and 18 were eligible for meta-analysis (study methods and references can be found in the online supplementary materials).1–5 Six of the 18 studies also included control groups. Overall, the frequency of taste alteration, smell alteration, and taste or smell alteration was reported in 41.3% (95% CI 21.1% to 65%), 45.3% (95% CI 23.3% to 69.4%), and 46.6% (95% CI 27% to 67.3%) in COVID-19 confirmed cases (table 1). The heterogeneity was high, but there was no significant publication bias (online supplementary materials). The frequency of taste or smell alteration was lower in studies from China (0.9%, 95% CI 0.2% to 3.7%) and Korea (12.2%, 95% CI 11.1% to 13.4%), compared with those from USA and Europe (41.3%, 95% CI 21.1% to 65%; online supplementary materials). The frequency of taste or smell alteration was higher in studies that recruited outpatients (63.9%, 95% CI 52.1% to 74.3%) than those that only recruited hospitalised patients (35.8%, 95% CI 29.6% to 42.4%; online supplementary materials).
The presence of taste or smell alteration was associated with increased risk (OR 6.5, 95% CI 5.2 to 8.1) of COVID-19 infection. The overall sensitivity, specificity, positive prediction value, negative predictive value, and accuracy of taste or smell alteration in the prediction of COVID-19 was 54.8% (95% CI 44.3% to 64.9%), 81.7% (95% CI 76.5% to 85.9%), 65.2% (95% CI 55.9% to 73.4%), 73.9% (95% CI 64.3% to 81.6%), and 71.8% (95% CI 67.5% to 75.6%), respectively (table 2).
This is the first systematic review and meta-analysis reporting the sensitivity and specificity of taste or smell alteration in the prediction of COVID-19. Our results showed that alteration of taste or smell is a common manifestation of COVID-19 in Western populations. However, these symptoms are rarely reported in studies from East Asia. Thus, the sensitivity of taste or smell alteration in the prediction of COVID-19 varies according to population and geography. Nevertheless, the specificity is high (81.7%) and the presence of taste or smell alteration is predictive of COVID-19 (positive prediction value 65.2%) and a confirmatory test is required in these subjects.
There are some limitations to this study. First, taste or smell alteration was not included in many reports from China or other East Asian countries. The relatively lower frequency of these symptoms in East Asia may be attributed to host genetic factors, variations of coronavirus or differential reporting. Second, only 6 of the 18 studies included COVID-19 negative control group and none from East Asia. Third, relatively few studies reported the clinical courses of taste or smell alteration. Of the studies that reported the clinical courses, complete resolution of taste or smell alteration was reported in 50%–70% of patients with COVID-19 within 2 weeks of symptom onset. More studies from other populations which include a COVID-19 control group and that address on the treatment, clinical course and pathogenesis of taste or smell alteration in COVID-19 are warranted.
Contributors J-ML designed the study and wrote the protocol. J-ML prepared the statistical analyses and drafted the article, which was critically revised and approved by all authors. All authors had full access to the data and participated in the decision to submit for publication.
Funding Supported by the Ministry of Science and Technology, Taiwan (grant number: TCTC 108-2321-B-002-040), the Ministry of Health and Welfare, Taiwan (MOHW108-CDC-C-114-112102), and the 'Center of Precision Medicine' of the Higher Education Sprout Project by the Ministry of Education (MOE), Taiwan (grant number: NTU-107L9014-1). The funding source had no role in study design, data collection, analysis, report writing or the decision to submit this paper for publication.
Competing interests None declared.
Patient and public involvement Patients and/or the public were not involved in the design, or conduct, or reporting, or dissemination plans of this research.
Patient consent for publication Not required.
Provenance and peer review Not commissioned; internally peer reviewed.
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