Olfactory loss is an early and reliable marker for COVID-19

Abstract

Detection of early and reliable symptoms is important in relation to limiting the spread of an infectious disease. For COVID-19, the most prevalent symptom is either losing or experiencing reduced olfactory functions. Anecdotal evidence suggests that olfactory dysfunction is also one of the earlier symptoms of COVID-19 but objective measures supporting this notion are currently missing. To determine whether olfactory dysfunction is an early sign of COVID-19, we assessed available longitudinal data from a web-based interface enabling individuals to test their sense of smell by rating the intensity of selected household odors. Individuals continuously used the interface to assess their olfactory functions and at each login, in addition to odor ratings, recorded their symptoms and result from potential COVID-19 test. A total of 205 COVID-19 positive individuals and 156 pseudo-randomly matched control individuals lacking positive test provided longitudinal data which enabled us to assess olfactory functions in relation to their test results date. We found that odor intensity ratings started to decline in the COVID-19 group as early as 6 days prior to test result date. Symptoms such as sore throat, aches, and runny nose appear around the same point in time; however, with a lower predictability of a COVID-19 diagnose. Our results suggest that olfactory dysfunction is an early symptom but does not appear before other related COVID-19 symptoms. Olfactory dysfunction is, however, more predictive of an COVID-19 diagnose than other early symptoms.

Competing Interest Statement

The authors have declared no competing interest.

Funding Statement

Funding provided by the Knut and Alice Wallenberg Foundation (KAW 2018.0152), the Swedish Research Council (2021-06527), and a donation from Stiftelsen Bygg-Gota for Vetenskaplig forskning.

Author Declarations

I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.

Yes

The details of the IRB/oversight body that provided approval or exemption for the research described are given below:

The study was approved by both the Israeli Edith Wolfson Medical Centre Helsinki Committee and the Swedish Institutional Review Board (Etikprovningsnamnden).

I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals.

Yes

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I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.

Yes

Data Availability

All data produced in the present study are available upon reasonable request to the authors

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